Internet-Draft Matroska Format October 2021
Lhomme, et al. Expires 12 April 2022 [Page]
Workgroup:
cellar
Internet-Draft:
draft-ietf-cellar-matroska-08
Published:
Intended Status:
Standards Track
Expires:
Authors:
S. Lhomme
M. Bunkus
D. Rice

Matroska Media Container Format Specifications

Abstract

This document defines the Matroska audiovisual container, including definitions of its structural elements, as well as its terminology, vocabulary, and application.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on 12 April 2022.

▲

Table of Contents

1. Introduction

Matroska aims to become THE standard of multimedia container formats. It was derived from a project called [MCF], but differentiates from it significantly because it is based on EBML (Extensible Binary Meta Language) [RFC8794], a binary derivative of XML. EBML enables significant advantages in terms of future format extensibility, without breaking file support in old parsers.

First, it is essential to clarify exactly "What an Audio/Video container is", to avoid any misunderstandings:

Matroska is designed with the future in mind. It incorporates features like:

Matroska is an open standards project. This means for personal use it is absolutely free to use and that the technical specifications describing the bitstream are open to everybody, even to companies that would like to support it in their products.

2. Status of this document

This document is a work-in-progress specification defining the Matroska file format as part of the IETF Cellar working group. But since it's quite complete it is used as a reference for the development of libmatroska.

Note that versions 1, 2, and 3 have been finalized. Version 4 is currently work in progress. There MAY be further additions to v4.

3. Security Considerations

Matroska inherits security considerations from EBML.

Attacks on a Matroska Reader could include:

4. Notation and Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

This document defines specific terms in order to define the format and application of Matroska. Specific terms are defined below:

Matroska:
A multimedia container format based on EBML (Extensible Binary Meta Language).
Matroska Reader:
A data parser that interprets the semantics of a Matroska document and creates a way for programs to use Matroska.
Matroska Player:
A Matroska Reader with a primary purpose of playing audiovisual files, including Matroska documents.

5. Basis in EBML

Matroska is a Document Type of EBML (Extensible Binary Meta Language). This specification is dependent on the EBML Specification [RFC8794]. For an understanding of Matroska's EBML Schema, see in particular the sections of the EBML Specification covering EBML Element Types (Section 7), EBML Schema (Section 11.1), and EBML Structure (Section 3).

5.1. Added Constraints on EBML

As an EBML Document Type, Matroska adds the following constraints to the EBML specification.

  • The docType of the EBML Header MUST be "matroska".
  • The EBMLMaxIDLength of the EBML Header MUST be "4".
  • The EBMLMaxSizeLength of the EBML Header MUST be between "1" and "8" inclusive.

5.2. Matroska Design

All top-levels elements (Segment and direct sub-elements) are coded on 4 octets -- i.e. class D elements.

6. Language Codes

Matroska from version 1 through 3 uses language codes that can be either the 3 letters bibliographic ISO-639-2 form [ISO639-2] (like "fre" for french), or such a language code followed by a dash and a country code for specialities in languages (like "fre-ca" for Canadian French). The ISO 639-2 Language Elements are "Language Element", "TagLanguage Element", and "ChapLanguage Element".

Starting in Matroska version 4, either [ISO639-2] or [BCP47] MAY be used, although BCP 47 is RECOMMENDED. The BCP 47 Language Elements are "LanguageIETF Element", "TagLanguageIETF Element", and "ChapLanguageIETF Element". If a BCP 47 Language Element and an ISO 639-2 Language Element are used within the same Parent Element, then the ISO 639-2 Language Element MUST be ignored and precedence given to the BCP 47 Language Element.

Country codes are the same 2 octets country-codes as in Internet domains [IANADomains] based on [ISO3166-1] alpha-2 codes.

7. Matroska Structure

A Matroska file MUST be composed of at least one EBML Document using the Matroska Document Type. Each EBML Document MUST start with an EBML Header and MUST be followed by the EBML Root Element, defined as Segment in Matroska. Matroska defines several Top Level Elements which MAY occur within the Segment.

As an example, a simple Matroska file consisting of a single EBML Document could be represented like this:

A more complex Matroska file consisting of an EBML Stream (consisting of two EBML Documents) could be represented like this:

The following diagram represents a simple Matroska file, comprised of an EBML Document with an EBML Header, a Segment Element (the Root Element), and all eight Matroska Top Level Elements. In the following diagrams of this section, horizontal spacing expresses a parent-child relationship between Matroska Elements (e.g., the Info Element is contained within the Segment Element) whereas vertical alignment represents the storage order within the file.

+-------------+
| EBML Header |
+---------------------------+
| Segment     | SeekHead    |
|             |-------------|
|             | Info        |
|             |-------------|
|             | Tracks      |
|             |-------------|
|             | Chapters    |
|             |-------------|
|             | Cluster     |
|             |-------------|
|             | Cues        |
|             |-------------|
|             | Attachments |
|             |-------------|
|             | Tags        |
+---------------------------+
Figure 1: Basic layout of a Matroska file.

The Matroska EBML Schema defines eight Top Level Elements: SeekHead, Info, Tracks, Chapters, Cluster, Cues, Attachments, and Tags.

The SeekHead Element (also known as MetaSeek) contains an index of Top Level Elements locations within the Segment. Use of the SeekHead Element is RECOMMENDED. Without a SeekHead Element, a Matroska parser would have to search the entire file to find all of the other Top Level Elements. This is due to Matroska's flexible ordering requirements; for instance, it is acceptable for the Chapters Element to be stored after the Cluster Elements.

+--------------------------------+
| SeekHead | Seek | SeekID       |
|          |      |--------------|
|          |      | SeekPosition |
+--------------------------------+
Figure 2: Representation of a SeekHead Element.

The Info Element contains vital information for identifying the whole Segment. This includes the title for the Segment, a randomly generated unique identifier, and the unique identifier(s) of any linked Segment Elements.

+-------------------------+
| Info | SegmentUID       |
|      |------------------|
|      | SegmentFilename  |
|      |------------------|
|      | PrevUID          |
|      |------------------|
|      | PrevFilename     |
|      |------------------|
|      | NextUID          |
|      |------------------|
|      | NextFilename     |
|      |------------------|
|      | SegmentFamily    |
|      |------------------|
|      | ChapterTranslate |
|      |------------------|
|      | TimestampScale   |
|      |------------------|
|      | Duration         |
|      |------------------|
|      | DateUTC          |
|      |------------------|
|      | Title            |
|      |------------------|
|      | MuxingApp        |
|      |------------------|
|      | WritingApp       |
|-------------------------|
Figure 3: Representation of an Info Element and its Child Elements.

The Tracks Element defines the technical details for each track and can store the name, number, unique identifier, language, and type (audio, video, subtitles, etc.) of each track. For example, the Tracks Element MAY store information about the resolution of a video track or sample rate of an audio track.

The Tracks Element MUST identify all the data needed by the codec to decode the data of the specified track. However, the data required is contingent on the codec used for the track. For example, a Track Element for uncompressed audio only requires the audio bit rate to be present. A codec such as AC-3 would require that the CodecID Element be present for all tracks, as it is the primary way to identify which codec to use to decode the track.

+------------------------------------+
| Tracks | TrackEntry | TrackNumber  |
|        |            |--------------|
|        |            | TrackUID     |
|        |            |--------------|
|        |            | TrackType    |
|        |            |--------------|
|        |            | Name         |
|        |            |--------------|
|        |            | Language     |
|        |            |--------------|
|        |            | CodecID      |
|        |            |--------------|
|        |            | CodecPrivate |
|        |            |--------------|
|        |            | CodecName    |
|        |            |----------------------------------+
|        |            | Video        | FlagInterlaced    |
|        |            |              |-------------------|
|        |            |              | FieldOrder        |
|        |            |              |-------------------|
|        |            |              | StereoMode        |
|        |            |              |-------------------|
|        |            |              | AlphaMode         |
|        |            |              |-------------------|
|        |            |              | PixelWidth        |
|        |            |              |-------------------|
|        |            |              | PixelHeight       |
|        |            |              |-------------------|
|        |            |              | DisplayWidth      |
|        |            |              |-------------------|
|        |            |              | DisplayHeight     |
|        |            |              |-------------------|
|        |            |              | AspectRatioType   |
|        |            |              |-------------------|
|        |            |              | Color             |
|        |            |----------------------------------|
|        |            | Audio        | SamplingFrequency |
|        |            |              |-------------------|
|        |            |              | Channels          |
|        |            |              |-------------------|
|        |            |              | BitDepth          |
|--------------------------------------------------------|
Figure 4: Representation of the Tracks Element and a selection of its Descendant Elements.

The Chapters Element lists all of the chapters. Chapters are a way to set predefined points to jump to in video or audio.

+-----------------------------------------+
| Chapters | Edition | EditionUID         |
|          | Entry   |--------------------|
|          |         | EditionFlagDefault |
|          |         |--------------------|
|          |         | EditionFlagOrdered |
|          |         |---------------------------------+
|          |         | ChapterAtom | ChapterUID        |
|          |         |             |-------------------|
|          |         |             | ChapterStringUID  |
|          |         |             |-------------------|
|          |         |             | ChapterTimeStart  |
|          |         |             |-------------------|
|          |         |             | ChapterTimeEnd    |
|          |         |             |-------------------|
|          |         |             | ChapterFlagHidden |
|          |         |             |-------------------------------+
|          |         |             | ChapterDisplay | ChapString   |
|          |         |             |                |--------------|
|          |         |             |                | ChapLanguage |
+------------------------------------------------------------------+
Figure 5: Representation of the Chapters Element and a selection of its Descendant Elements.

Cluster Elements contain the content for each track, e.g., video frames. A Matroska file SHOULD contain at least one Cluster Element. The Cluster Element helps to break up SimpleBlock or BlockGroup Elements and helps with seeking and error protection. It is RECOMMENDED that the size of each individual Cluster Element be limited to store no more than 5 seconds or 5 megabytes. Every Cluster Element MUST contain a Timestamp Element. This SHOULD be the Timestamp Element used to play the first Block in the Cluster Element. There SHOULD be one or more BlockGroup or SimpleBlock Element in each Cluster Element. A BlockGroup Element MAY contain a Block of data and any information relating directly to that Block.

+--------------------------+
| Cluster | Timestamp      |
|         |----------------|
|         | SilentTracks   |
|         |----------------|
|         | Position       |
|         |----------------|
|         | PrevSize       |
|         |----------------|
|         | SimpleBlock    |
|         |----------------|
|         | BlockGroup     |
|         |----------------|
|         | EncryptedBlock |
+--------------------------+
Figure 6: Representation of a Cluster Element and its immediate Child Elements. 
+----------------------------------+
| Block | Portion of | Data Type   |
|       | a Block    |  - Bit Flag |
|       |--------------------------+
|       | Header     | TrackNumber |
|       |            |-------------|
|       |            | Timestamp   |
|       |            |-------------|
|       |            | Flags       |
|       |            |  - Gap      |
|       |            |  - Lacing   |
|       |            |  - Reserved |
|       |--------------------------|
|       | Optional   | FrameSize   |
|       |--------------------------|
|       | Data       | Frame       |
+----------------------------------+
Figure 7: Representation of the Block Element structure.

Each Cluster MUST contain exactly one Timestamp Element. The Timestamp Element value MUST be stored once per Cluster. The Timestamp Element in the Cluster is relative to the entire Segment. The Timestamp Element SHOULD be the first Element in the Cluster.

Additionally, the Block contains an offset that, when added to the Cluster's Timestamp Element value, yields the Block's effective timestamp. Therefore, timestamp in the Block itself is relative to the Timestamp Element in the Cluster. For example, if the Timestamp Element in the Cluster is set to 10 seconds and a Block in that Cluster is supposed to be played 12 seconds into the clip, the timestamp in the Block would be set to 2 seconds.

The ReferenceBlock in the BlockGroup is used instead of the basic "P-frame"/"B-frame" description. Instead of simply saying that this Block depends on the Block directly before, or directly afterwards, the Timestamp of the necessary Block is used. Because there can be as many ReferenceBlock Elements as necessary for a Block, it allows for some extremely complex referencing.

The Cues Element is used to seek when playing back a file by providing a temporal index for some of the Tracks. It is similar to the SeekHead Element, but used for seeking to a specific time when playing back the file. It is possible to seek without this element, but it is much more difficult because a Matroska Reader would have to 'hunt and peck' through the file looking for the correct timestamp.

The Cues Element SHOULD contain at least one CuePoint Element. Each CuePoint Element stores the position of the Cluster that contains the BlockGroup or SimpleBlock Element. The timestamp is stored in the CueTime Element and location is stored in the CueTrackPositions Element.

The Cues Element is flexible. For instance, Cues Element can be used to index every single timestamp of every Block or they can be indexed selectively. For video files, it is RECOMMENDED to index at least the keyframes of the video track.

+-------------------------------------+
| Cues | CuePoint | CueTime           |
|      |          |-------------------|
|      |          | CueTrackPositions |
|      |------------------------------|
|      | CuePoint | CueTime           |
|      |          |-------------------|
|      |          | CueTrackPositions |
+-------------------------------------+
Figure 8: Representation of a Cues Element and two levels of its Descendant Elements.

The Attachments Element is for attaching files to a Matroska file such as pictures, webpages, programs, or even the codec needed to play back the file.

+------------------------------------------------+
| Attachments | AttachedFile | FileDescription   |
|             |              |-------------------|
|             |              | FileName          |
|             |              |-------------------|
|             |              | FileMimeType      |
|             |              |-------------------|
|             |              | FileData          |
|             |              |-------------------|
|             |              | FileUID           |
|             |              |-------------------|
|             |              | FileName          |
|             |              |-------------------|
|             |              | FileReferral      |
|             |              |-------------------|
|             |              | FileUsedStartTime |
|             |              |-------------------|
|             |              | FileUsedEndTime   |
+------------------------------------------------+
Figure 9: Representation of a Attachments Element.

The Tags Element contains metadata that describes the Segment and potentially its Tracks, Chapters, and Attachments. Each Track or Chapter that those tags applies to has its UID listed in the Tags. The Tags contain all extra information about the file: scriptwriter, singer, actors, directors, titles, edition, price, dates, genre, comments, etc. Tags can contain their values in multiple languages. For example, a movie's "title" Tag might contain both the original English title as well as the title it was released as in Germany.

+-------------------------------------------+
| Tags | Tag | Targets   | TargetTypeValue  |
|      |     |           |------------------|
|      |     |           | TargetType       |
|      |     |           |------------------|
|      |     |           | TagTrackUID      |
|      |     |           |------------------|
|      |     |           | TagEditionUID    |
|      |     |           |------------------|
|      |     |           | TagChapterUID    |
|      |     |           |------------------|
|      |     |           | TagAttachmentUID |
|      |     |------------------------------|
|      |     | SimpleTag | TagName          |
|      |     |           |------------------|
|      |     |           | TagLanguage      |
|      |     |           |------------------|
|      |     |           | TagDefault       |
|      |     |           |------------------|
|      |     |           | TagString        |
|      |     |           |------------------|
|      |     |           | TagBinary        |
|      |     |           |------------------|
|      |     |           | SimpleTag        |
+-------------------------------------------+
Figure 10: Representation of a Tags Element and three levels of its Children Elements.

8. Matroska Schema

This specification includes an EBML Schema, which defines the Elements and structure of Matroska as an EBML Document Type. The EBML Schema defines every valid Matroska element in a manner defined by the EBML specification.

Here the definition of each Matroska Element is provided.

8.1. Segment Element

name:
Segment
path:
\Segment
id:
0x18538067
minOccurs:
1
maxOccurs:
1
type:
master
unknownsizeallowed:
1
definition:
The Root Element that contains all other Top-Level Elements (Elements defined only at Level 1). A Matroska file is composed of 1 Segment.

8.1.1. SeekHead Element

name:
SeekHead
path:
\Segment\SeekHead
id:
0x114D9B74
maxOccurs:
2
type:
master
definition:
Contains the Segment Position of other Top-Level Elements.
8.1.1.1. Seek Element
name:
Seek
path:
\Segment\SeekHead\Seek
id:
0x4DBB
minOccurs:
1
type:
master
definition:
Contains a single seek entry to an EBML Element.
8.1.1.1.1. SeekID Element
name:
SeekID
path:
\Segment\SeekHead\Seek\SeekID
id:
0x53AB
minOccurs:
1
maxOccurs:
1
type:
binary
definition:
The binary ID corresponding to the Element name.
8.1.1.1.2. SeekPosition Element
name:
SeekPosition
path:
\Segment\SeekHead\Seek\SeekPosition
id:
0x53AC
minOccurs:
1
maxOccurs:
1
type:
uinteger
definition:
The Segment Position of the Element.

8.1.2. Info Element

name:
Info
path:
\Segment\Info
id:
0x1549A966
minOccurs:
1
maxOccurs:
1
type:
master
recurring:
1
definition:
Contains general information about the Segment.
8.1.2.1. SegmentUID Element
name:
SegmentUID
path:
\Segment\Info\SegmentUID
id:
0x73A4
maxOccurs:
1
range:
not 0
type:
binary
definition:
A randomly generated unique ID to identify the Segment amongst many others (128 bits).
usage notes:
If the Segment is a part of a Linked Segment, then this Element is REQUIRED.
8.1.2.2. SegmentFilename Element
name:
SegmentFilename
path:
\Segment\Info\SegmentFilename
id:
0x7384
maxOccurs:
1
type:
utf-8
definition:
A filename corresponding to this Segment.
8.1.2.3. PrevUID Element
name:
PrevUID
path:
\Segment\Info\PrevUID
id:
0x3CB923
maxOccurs:
1
type:
binary
definition:
A unique ID to identify the previous Segment of a Linked Segment (128 bits).
usage notes:
If the Segment is a part of a Linked Segment that uses Hard Linking, then either the PrevUID or the NextUID Element is REQUIRED. If a Segment contains a PrevUID but not a NextUID, then it MAY be considered as the last Segment of the Linked Segment. The PrevUID MUST NOT be equal to the SegmentUID.
8.1.2.4. PrevFilename Element
name:
PrevFilename
path:
\Segment\Info\PrevFilename
id:
0x3C83AB
maxOccurs:
1
type:
utf-8
definition:
A filename corresponding to the file of the previous Linked Segment.
usage notes:
Provision of the previous filename is for display convenience, but PrevUID SHOULD be considered authoritative for identifying the previous Segment in a Linked Segment.
8.1.2.5. NextUID Element
name:
NextUID
path:
\Segment\Info\NextUID
id:
0x3EB923
maxOccurs:
1
type:
binary
definition:
A unique ID to identify the next Segment of a Linked Segment (128 bits).
usage notes:
If the Segment is a part of a Linked Segment that uses Hard Linking, then either the PrevUID or the NextUID Element is REQUIRED. If a Segment contains a NextUID but not a PrevUID, then it MAY be considered as the first Segment of the Linked Segment. The NextUID MUST NOT be equal to the SegmentUID.
8.1.2.6. NextFilename Element
name:
NextFilename
path:
\Segment\Info\NextFilename
id:
0x3E83BB
maxOccurs:
1
type:
utf-8
definition:
A filename corresponding to the file of the next Linked Segment.
usage notes:
Provision of the next filename is for display convenience, but NextUID SHOULD be considered authoritative for identifying the Next Segment.
8.1.2.7. SegmentFamily Element
name:
SegmentFamily
path:
\Segment\Info\SegmentFamily
id:
0x4444
type:
binary
definition:
A randomly generated unique ID that all Segments of a Linked Segment MUST share (128 bits).
usage notes:
If the Segment is a part of a Linked Segment that uses Soft Linking, then this Element is REQUIRED.
8.1.2.8. ChapterTranslate Element
name:
ChapterTranslate
path:
\Segment\Info\ChapterTranslate
id:
0x6924
type:
master
definition:
A tuple of corresponding ID used by chapter codecs to represent this Segment.
8.1.2.8.1. ChapterTranslateEditionUID Element
name:
ChapterTranslateEditionUID
path:
\Segment\Info\ChapterTranslate\ChapterTranslateEditionUID
id:
0x69FC
type:
uinteger
definition:
Specify an edition UID on which this correspondence applies. When not specified, it means for all editions found in the Segment.
8.1.2.8.2. ChapterTranslateCodec Element
name:
ChapterTranslateCodec
path:
\Segment\Info\ChapterTranslate\ChapterTranslateCodec
id:
0x69BF
minOccurs:
1
maxOccurs:
1
type:
uinteger
definition:
The chapter codec; see Section 8.1.7.1.4.15.

restrictions:

Table 1: ChapterTranslateCodec values
value label
0 Matroska Script
1 DVD-menu
8.1.2.8.3. ChapterTranslateID Element
name:
ChapterTranslateID
path:
\Segment\Info\ChapterTranslate\ChapterTranslateID
id:
0x69A5
minOccurs:
1
maxOccurs:
1
type:
binary
definition:
The binary value used to represent this Segment in the chapter codec data. The format depends on the ChapProcessCodecID used; see Section 8.1.7.1.4.15.
8.1.2.9. TimestampScale Element
name:
TimestampScale
path:
\Segment\Info\TimestampScale
id:
0x2AD7B1
minOccurs:
1
maxOccurs:
1
range:
not 0
default:
1000000
type:
uinteger
definition:
Timestamp scale in nanoseconds (1.000.000 means all timestamps in the Segment are expressed in milliseconds).
8.1.2.10. Duration Element
name:
Duration
path:
\Segment\Info\Duration
id:
0x4489
maxOccurs:
1
range:
> 0x0p+0
type:
float
definition:
Duration of the Segment in nanoseconds based on TimestampScale.
8.1.2.11. DateUTC Element
name:
DateUTC
path:
\Segment\Info\DateUTC
id:
0x4461
maxOccurs:
1
type:
date
definition:
The date and time that the Segment was created by the muxing application or library.
8.1.2.12. Title Element
name:
Title
path:
\Segment\Info\Title
id:
0x7BA9
maxOccurs:
1
type:
utf-8
definition:
General name of the Segment.
8.1.2.13. MuxingApp Element
name:
MuxingApp
path:
\Segment\Info\MuxingApp
id:
0x4D80
minOccurs:
1
maxOccurs:
1
type:
utf-8
definition:
Muxing application or library (example: "libmatroska-0.4.3").
usage notes:
Include the full name of the application or library followed by the version number.
8.1.2.14. WritingApp Element
name:
WritingApp
path:
\Segment\Info\WritingApp
id:
0x5741
minOccurs:
1
maxOccurs:
1
type:
utf-8
definition:
Writing application (example: "mkvmerge-0.3.3").
usage notes:
Include the full name of the application followed by the version number.

8.1.3. Cluster Element

name:
Cluster
path:
\Segment\Cluster
id:
0x1F43B675
type:
master
unknownsizeallowed:
1
definition:
The Top-Level Element containing the (monolithic) Block structure.
8.1.3.1. Timestamp Element
name:
Timestamp
path:
\Segment\Cluster\Timestamp
id:
0xE7
minOccurs:
1
maxOccurs:
1
type:
uinteger
definition:
Absolute timestamp of the cluster (based on TimestampScale).
8.1.3.2. Position Element
name:
Position
path:
\Segment\Cluster\Position
id:
0xA7
maxOccurs:
1
type:
uinteger
definition:
The Segment Position of the Cluster in the Segment (0 in live streams). It might help to resynchronise offset on damaged streams.
8.1.3.3. PrevSize Element
name:
PrevSize
path:
\Segment\Cluster\PrevSize
id:
0xAB
maxOccurs:
1
type:
uinteger
definition:
Size of the previous Cluster, in octets. Can be useful for backward playing.
8.1.3.4. SimpleBlock Element
name:
SimpleBlock
path:
\Segment\Cluster\SimpleBlock
id:
0xA3
type:
binary
minver:
2
definition:
Similar to Block, see Section 12, but without all the extra information, mostly used to reduced overhead when no extra feature is needed; see Section 12.4 on SimpleBlock Structure.
8.1.3.5. BlockGroup Element
name:
BlockGroup
path:
\Segment\Cluster\BlockGroup
id:
0xA0
type:
master
definition:
Basic container of information containing a single Block and information specific to that Block.
8.1.3.5.1. Block Element
name:
Block
path:
\Segment\Cluster\BlockGroup\Block
id:
0xA1
minOccurs:
1
maxOccurs:
1
type:
binary
definition:
Block containing the actual data to be rendered and a timestamp relative to the Cluster Timestamp; see Section 12 on Block Structure.
8.1.3.5.2. BlockAdditions Element
name:
BlockAdditions
path:
\Segment\Cluster\BlockGroup\BlockAdditions
id:
0x75A1
maxOccurs:
1
type:
master
definition:
Contain additional blocks to complete the main one. An EBML parser that has no knowledge of the Block structure could still see and use/skip these data.
8.1.3.5.2.1. BlockMore Element
name:
BlockMore
path:
\Segment\Cluster\BlockGroup\BlockAdditions\BlockMore
id:
0xA6
minOccurs:
1
type:
master
definition:
Contain the BlockAdditional and some parameters.
8.1.3.5.2.2. BlockAddID Element
name:
BlockAddID
path:
\Segment\Cluster\BlockGroup\BlockAdditions\BlockMore\BlockAddID
id:
0xEE
minOccurs:
1
maxOccurs:
1
range:
not 0
default:
1
type:
uinteger
definition:
An ID to identify the BlockAdditional level. If BlockAddIDType of the corresponding block is 0, this value is also the value of BlockAddIDType for the meaning of the content of BlockAdditional.
8.1.3.5.2.3. BlockAdditional Element
name:
BlockAdditional
path:
\Segment\Cluster\BlockGroup\BlockAdditions\BlockMore\BlockAdditional
id:
0xA5
minOccurs:
1
maxOccurs:
1
type:
binary
definition:
Interpreted by the codec as it wishes (using the BlockAddID).
8.1.3.5.3. BlockDuration Element
name:
BlockDuration
path:
\Segment\Cluster\BlockGroup\BlockDuration
id:
0x9B

minOccurs: see implementation notes

maxOccurs:
1

default: see implementation notes

type:
uinteger
definition:
The duration of the Block (based on TimestampScale). The BlockDuration Element can be useful at the end of a Track to define the duration of the last frame (as there is no subsequent Block available), or when there is a break in a track like for subtitle tracks.

notes:

Table 2: BlockDuration implementation notes
attribute note
minOccurs BlockDuration MUST be set (minOccurs=1) if the associated TrackEntry stores a DefaultDuration value.
default When not written and with no DefaultDuration, the value is assumed to be the difference between the timestampof this Block and the timestamp of the next Block in "display" order (not coding order).
8.1.3.5.4. ReferencePriority Element
name:
ReferencePriority
path:
\Segment\Cluster\BlockGroup\ReferencePriority
id:
0xFA
minOccurs:
1
maxOccurs:
1
default:
0
type:
uinteger
definition:
This frame is referenced and has the specified cache priority. In cache only a frame of the same or higher priority can replace this frame. A value of 0 means the frame is not referenced.
8.1.3.5.5. ReferenceBlock Element
name:
ReferenceBlock
path:
\Segment\Cluster\BlockGroup\ReferenceBlock
id:
0xFB
type:
integer
definition:
Timestamp of another frame used as a reference (ie: B or P frame). The timestamp is relative to the block it's attached to.
8.1.3.5.6. CodecState Element
name:
CodecState
path:
\Segment\Cluster\BlockGroup\CodecState
id:
0xA4
maxOccurs:
1
type:
binary
minver:
2
definition:
The new codec state to use. Data interpretation is private to the codec. This information SHOULD always be referenced by a seek entry.
8.1.3.5.7. DiscardPadding Element
name:
DiscardPadding
path:
\Segment\Cluster\BlockGroup\DiscardPadding
id:
0x75A2
maxOccurs:
1
type:
integer
minver:
4
definition:
Duration in nanoseconds of the silent data added to the Block (padding at the end of the Block for positive value, at the beginning of the Block for negative value). The duration of DiscardPadding is not calculated in the duration of the TrackEntry and SHOULD be discarded during playback.
8.1.3.5.8. Slices Element
name:
Slices
path:
\Segment\Cluster\BlockGroup\Slices
id:
0x8E
maxOccurs:
1
type:
master
maxver:
1
definition:
Contains slices description.
8.1.3.5.8.1. TimeSlice Element
name:
TimeSlice
path:
\Segment\Cluster\BlockGroup\Slices\TimeSlice
id:
0xE8
type:
master
maxver:
1
definition:
Contains extra time information about the data contained in the Block. Being able to interpret this Element is not REQUIRED for playback.
8.1.3.5.8.2. LaceNumber Element
name:
LaceNumber
path:
\Segment\Cluster\BlockGroup\Slices\TimeSlice\LaceNumber
id:
0xCC
maxOccurs:
1
type:
uinteger
maxver:
1
definition:
The reverse number of the frame in the lace (0 is the last frame, 1 is the next to last, etc). Being able to interpret this Element is not REQUIRED for playback.

8.1.4. Tracks Element

name:
Tracks
path:
\Segment\Tracks
id:
0x1654AE6B
maxOccurs:
1
type:
master
recurring:
1
definition:
A Top-Level Element of information with many tracks described.
8.1.4.1. TrackEntry Element
name:
TrackEntry
path:
\Segment\Tracks\TrackEntry
id:
0xAE
minOccurs:
1
type:
master
definition:
Describes a track with all Elements.
8.1.4.1.1. TrackNumber Element
name:
TrackNumber
path:
\Segment\Tracks\TrackEntry\TrackNumber
id:
0xD7
minOccurs:
1
maxOccurs:
1
range:
not 0
type:
uinteger
definition:
The track number as used in the Block Header (using more than 127 tracks is not encouraged, though the design allows an unlimited number).
8.1.4.1.2. TrackUID Element
name:
TrackUID
path:
\Segment\Tracks\TrackEntry\TrackUID
id:
0x73C5
minOccurs:
1
maxOccurs:
1
range:
not 0
type:
uinteger
definition:
A unique ID to identify the Track.
usage notes:
The value of this Element SHOULD be kept the same when making a direct stream copy to another file.
8.1.4.1.3. TrackType Element
name:
TrackType
path:
\Segment\Tracks\TrackEntry\TrackType
id:
0x83
minOccurs:
1
maxOccurs:
1
type:
uinteger
definition:
A set of track types coded on 8 bits.

restrictions:

Table 3: TrackType values
value label
1 video
2 audio
3 complex
16 logo
17 subtitle
18 buttons
32 control
33 metadata
8.1.4.1.4. FlagEnabled Element
name:
FlagEnabled
path:
\Segment\Tracks\TrackEntry\FlagEnabled
id:
0xB9
minOccurs:
1
maxOccurs:
1
range:
0-1
default:
1
type:
uinteger
minver:
2
definition:
Set to 1 if the track is usable. It is possible to turn a not usable track into a usable track using chapter codecs or control tracks.
8.1.4.1.5. FlagDefault Element
name:
FlagDefault
path:
\Segment\Tracks\TrackEntry\FlagDefault
id:
0x88
minOccurs:
1
maxOccurs:
1
range:
0-1
default:
1
type:
uinteger
definition:
Set if that track (audio, video or subs) SHOULD be eligible for automatic selection by the player; see Section 21 for more details.
8.1.4.1.6. FlagForced Element
name:
FlagForced
path:
\Segment\Tracks\TrackEntry\FlagForced
id:
0x55AA
minOccurs:
1
maxOccurs:
1
range:
0-1
default:
0
type:
uinteger
definition:
Applies only to subtitles. Set if that track SHOULD be eligible for automatic selection by the player if it matches the user's language preference, even if the user's preferences would normally not enable subtitles with the selected audio track; this can be used for tracks containing only translations of foreign-language audio or onscreen text. See Section 21 for more details.
8.1.4.1.7. FlagHearingImpaired Element
name:
FlagHearingImpaired
path:
\Segment\Tracks\TrackEntry\FlagHearingImpaired
id:
0x55AB
maxOccurs:
1
range:
0-1
type:
uinteger
minver:
4
definition:
Set to 1 if that track is suitable for users with hearing impairments, set to 0 if it is unsuitable for users with hearing impairments.
8.1.4.1.8. FlagVisualImpaired Element
name:
FlagVisualImpaired
path:
\Segment\Tracks\TrackEntry\FlagVisualImpaired
id:
0x55AC
maxOccurs:
1
range:
0-1
type:
uinteger
minver:
4
definition:
Set to 1 if that track is suitable for users with visual impairments, set to 0 if it is unsuitable for users with visual impairments.
8.1.4.1.9. FlagTextDescriptions Element
name:
FlagTextDescriptions
path:
\Segment\Tracks\TrackEntry\FlagTextDescriptions
id:
0x55AD
maxOccurs:
1
range:
0-1
type:
uinteger
minver:
4
definition:
Set to 1 if that track contains textual descriptions of video content, set to 0 if that track does not contain textual descriptions of video content.
8.1.4.1.10. FlagOriginal Element
name:
FlagOriginal
path:
\Segment\Tracks\TrackEntry\FlagOriginal
id:
0x55AE
maxOccurs:
1
range:
0-1
type:
uinteger
minver:
4
definition:
Set to 1 if that track is in the content's original language, set to 0 if it is a translation.
8.1.4.1.11. FlagCommentary Element
name:
FlagCommentary
path:
\Segment\Tracks\TrackEntry\FlagCommentary
id:
0x55AF
maxOccurs:
1
range:
0-1
type:
uinteger
minver:
4
definition:
Set to 1 if that track contains commentary, set to 0 if it does not contain commentary.
8.1.4.1.12. FlagLacing Element
name:
FlagLacing
path:
\Segment\Tracks\TrackEntry\FlagLacing
id:
0x9C
minOccurs:
1
maxOccurs:
1
range:
0-1
default:
1
type:
uinteger
definition:
Set to 1 if the track MAY contain blocks using lacing.
8.1.4.1.13. MinCache Element
name:
MinCache
path:
\Segment\Tracks\TrackEntry\MinCache
id:
0x6DE7
minOccurs:
1
maxOccurs:
1
default:
0
type:
uinteger
definition:
The minimum number of frames a player SHOULD be able to cache during playback. If set to 0, the reference pseudo-cache system is not used.
8.1.4.1.14. MaxCache Element
name:
MaxCache
path:
\Segment\Tracks\TrackEntry\MaxCache
id:
0x6DF8
maxOccurs:
1
type:
uinteger
definition:
The maximum cache size necessary to store referenced frames in and the current frame. 0 means no cache is needed.
8.1.4.1.15. DefaultDuration Element
name:
DefaultDuration
path:
\Segment\Tracks\TrackEntry\DefaultDuration
id:
0x23E383
maxOccurs:
1
range:
not 0
type:
uinteger
definition:
Number of nanoseconds (not scaled via TimestampScale) per frame (frame in the Matroska sense -- one Element put into a (Simple)Block).
8.1.4.1.16. DefaultDecodedFieldDuration Element
name:
DefaultDecodedFieldDuration
path:
\Segment\Tracks\TrackEntry\DefaultDecodedFieldDuration
id:
0x234E7A
maxOccurs:
1
range:
not 0
type:
uinteger
minver:
4
definition:
The period in nanoseconds (not scaled by TimestampScale) between two successive fields at the output of the decoding process, see Section 11 for more information
8.1.4.1.17. TrackTimestampScale Element
name:
TrackTimestampScale
path:
\Segment\Tracks\TrackEntry\TrackTimestampScale
id:
0x23314F
minOccurs:
1
maxOccurs:
1
range:
> 0x0p+0
default:
0x1p+0
type:
float
maxver:
3
definition:
DEPRECATED, DO NOT USE. The scale to apply on this track to work at normal speed in relation with other tracks (mostly used to adjust video speed when the audio length differs).
8.1.4.1.18. MaxBlockAdditionID Element
name:
MaxBlockAdditionID
path:
\Segment\Tracks\TrackEntry\MaxBlockAdditionID
id:
0x55EE
minOccurs:
1
maxOccurs:
1
default:
0
type:
uinteger
definition:
The maximum value of BlockAddID (Section 8.1.3.5.2.2). A value 0 means there is no BlockAdditions (Section 8.1.3.5.2) for this track.
8.1.4.1.19. BlockAdditionMapping Element
name:
BlockAdditionMapping
path:
\Segment\Tracks\TrackEntry\BlockAdditionMapping
id:
0x41E4
type:
master
minver:
4
definition:
Contains elements that extend the track format, by adding content either to each frame, with BlockAddID (Section 8.1.3.5.2.2), or to the track as a whole with BlockAddIDExtraData.
8.1.4.1.19.1. BlockAddIDValue Element
name:
BlockAddIDValue
path:
\Segment\Tracks\TrackEntry\BlockAdditionMapping\BlockAddIDValue
id:
0x41F0
maxOccurs:
1
range:
>=2
type:
uinteger
minver:
4
definition:
If the track format extension needs content beside frames, the value refers to the BlockAddID (Section 8.1.3.5.2.2), value being described. To keep MaxBlockAdditionID as low as possible, small values SHOULD be used.
8.1.4.1.19.2. BlockAddIDName Element
name:
BlockAddIDName
path:
\Segment\Tracks\TrackEntry\BlockAdditionMapping\BlockAddIDName
id:
0x41A4
maxOccurs:
1
type:
string
minver:
4
definition:
A human-friendly name describing the type of BlockAdditional data, as defined by the associated Block Additional Mapping.
8.1.4.1.19.3. BlockAddIDType Element
name:
BlockAddIDType
path:
\Segment\Tracks\TrackEntry\BlockAdditionMapping\BlockAddIDType
id:
0x41E7
minOccurs:
1
maxOccurs:
1
default:
0
type:
uinteger
minver:
4
definition:
Stores the registered identifier of the Block Additional Mapping to define how the BlockAdditional data should be handled.
8.1.4.1.19.4. BlockAddIDExtraData Element
name:
BlockAddIDExtraData
path:
\Segment\Tracks\TrackEntry\BlockAdditionMapping\BlockAddIDExtraData
id:
0x41ED
maxOccurs:
1
type:
binary
minver:
4
definition:
Extra binary data that the BlockAddIDType can use to interpret the BlockAdditional data. The interpretation of the binary data depends on the BlockAddIDType value and the corresponding Block Additional Mapping.
8.1.4.1.20. Name Element
name:
Name
path:
\Segment\Tracks\TrackEntry\Name
id:
0x536E
maxOccurs:
1
type:
utf-8
definition:
A human-readable track name.
8.1.4.1.21. Language Element
name:
Language
path:
\Segment\Tracks\TrackEntry\Language
id:
0x22B59C
minOccurs:
1
maxOccurs:
1
default:
eng
type:
string
definition:
Specifies the language of the track in the Matroska languages form; see Section 6 on language codes. This Element MUST be ignored if the LanguageIETF Element is used in the same TrackEntry.
8.1.4.1.22. LanguageIETF Element
name:
LanguageIETF
path:
\Segment\Tracks\TrackEntry\LanguageIETF
id:
0x22B59D
maxOccurs:
1
type:
string
minver:
4
definition:
Specifies the language of the track according to [BCP47] and using the IANA Language Subtag Registry [IANALangRegistry]. If this Element is used, then any Language Elements used in the same TrackEntry MUST be ignored.
8.1.4.1.23. CodecID Element
name:
CodecID
path:
\Segment\Tracks\TrackEntry\CodecID
id:
0x86
minOccurs:
1
maxOccurs:
1
type:
string
definition:
An ID corresponding to the codec, see [MatroskaCodec] for more info.
8.1.4.1.24. CodecPrivate Element
name:
CodecPrivate
path:
\Segment\Tracks\TrackEntry\CodecPrivate
id:
0x63A2
maxOccurs:
1
type:
binary
definition:
Private data only known to the codec.
8.1.4.1.25. CodecName Element
name:
CodecName
path:
\Segment\Tracks\TrackEntry\CodecName
id:
0x258688
maxOccurs:
1
type:
utf-8
definition:
A human-readable string specifying the codec.
8.1.4.1.27. TrackOverlay Element
name:
TrackOverlay
path:
\Segment\Tracks\TrackEntry\TrackOverlay
id:
0x6FAB
type:
uinteger
definition:
Specify that this track is an overlay track for the Track specified (in the u-integer). That means when this track has a gap, see Section 26.3.1 on SilentTracks, the overlay track SHOULD be used instead. The order of multiple TrackOverlay matters, the first one is the one that SHOULD be used. If not found it SHOULD be the second, etc.
8.1.4.1.28. CodecDelay Element
name:
CodecDelay
path:
\Segment\Tracks\TrackEntry\CodecDelay
id:
0x56AA
maxOccurs:
1
type:
uinteger
minver:
4
definition:
CodecDelay is The codec-built-in delay in nanoseconds. This value MUST be subtracted from each block timestamp in order to get the actual timestamp. The value SHOULD be small so the muxing of tracks with the same actual timestamp are in the same Cluster.
8.1.4.1.29. SeekPreRoll Element
name:
SeekPreRoll
path:
\Segment\Tracks\TrackEntry\SeekPreRoll
id:
0x56BB
minOccurs:
1
maxOccurs:
1
default:
0
type:
uinteger
minver:
4
definition:
After a discontinuity, SeekPreRoll is the duration in nanoseconds of the data the decoder MUST decode before the decoded data is valid.
8.1.4.1.30. TrackTranslate Element
name:
TrackTranslate
path:
\Segment\Tracks\TrackEntry\TrackTranslate
id:
0x6624
type:
master
definition:
The track identification for the given Chapter Codec.
8.1.4.1.30.1. TrackTranslateEditionUID Element
name:
TrackTranslateEditionUID
path:
\Segment\Tracks\TrackEntry\TrackTranslate\TrackTranslateEditionUID
id:
0x66FC
type:
uinteger
definition:
Specify an edition UID on which this translation applies. When not specified, it means for all editions found in the Segment.
8.1.4.1.30.2. TrackTranslateCodec Element
name:
TrackTranslateCodec
path:
\Segment\Tracks\TrackEntry\TrackTranslate\TrackTranslateCodec
id:
0x66BF
minOccurs:
1
maxOccurs:
1
type:
uinteger
definition:
The chapter codec; see Section 8.1.7.1.4.15.

restrictions:

Table 4: TrackTranslateCodec values
value label
0 Matroska Script
1 DVD-menu
8.1.4.1.30.3. TrackTranslateTrackID Element
name:
TrackTranslateTrackID
path:
\Segment\Tracks\TrackEntry\TrackTranslate\TrackTranslateTrackID
id:
0x66A5
minOccurs:
1
maxOccurs:
1
type:
binary
definition:
The binary value used to represent this track in the chapter codec data. The format depends on the ChapProcessCodecID used; see Section 8.1.7.1.4.15.
8.1.4.1.31. Video Element
name:
Video
path:
\Segment\Tracks\TrackEntry\Video
id:
0xE0
maxOccurs:
1
type:
master
definition:
Video settings.
8.1.4.1.31.1. FlagInterlaced Element
name:
FlagInterlaced
path:
\Segment\Tracks\TrackEntry\Video\FlagInterlaced
id:
0x9A
minOccurs:
1
maxOccurs:
1
default:
0
type:
uinteger
minver:
2
definition:
Specify whether the video frames in this track are interlaced or not.

defined values:

Table 5: FlagInterlaced values
value label definition
0 undetermined Unknown status.This value SHOULD be avoided.
1 interlaced Interlaced frames.
2 progressive No interlacing.
8.1.4.1.31.2. FieldOrder Element
name:
FieldOrder
path:
\Segment\Tracks\TrackEntry\Video\FieldOrder
id:
0x9D
minOccurs:
1
maxOccurs:
1
default:
2
type:
uinteger
minver:
4
definition:
Specify the field ordering of video frames in this track.
usage notes:
If FlagInterlaced is not set to 1, this Element MUST be ignored.

defined values:

Table 6: FieldOrder values
value label definition
0 progressive Interlaced frames.This value SHOULD be avoided, setting FlagInterlaced to 2 is sufficient.
1 tff Top field displayed first. Top field stored first.
2 undetermined Unknown field order.This value SHOULD be avoided.
6 bff Bottom field displayed first. Bottom field stored first.
9 bff(swapped) Top field displayed first. Fields are interleaved in storage
with the top line of the top field stored first.
14 tff(swapped) Bottom field displayed first. Fields are interleaved in storage
with the top line of the top field stored first.
8.1.4.1.31.3. StereoMode Element
name:
StereoMode
path:
\Segment\Tracks\TrackEntry\Video\StereoMode
id:
0x53B8
minOccurs:
1
maxOccurs:
1
default:
0
type:
uinteger
minver:
3
definition:
Stereo-3D video mode. There are some more details in Section 20.10.

restrictions:

Table 7: StereoMode values
value label
0 mono
1 side by side (left eye first)
2 top - bottom (right eye is first)
3 top - bottom (left eye is first)
4 checkboard (right eye is first)
5 checkboard (left eye is first)
6 row interleaved (right eye is first)
7 row interleaved (left eye is first)
8 column interleaved (right eye is first)
9 column interleaved (left eye is first)
10 anaglyph (cyan/red)
11 side by side (right eye first)
12 anaglyph (green/magenta)
13 both eyes laced in one Block (left eye is first)
14 both eyes laced in one Block (right eye is first)
8.1.4.1.31.4. AlphaMode Element
name:
AlphaMode
path:
\Segment\Tracks\TrackEntry\Video\AlphaMode
id:
0x53C0
maxOccurs:
1
default:
0
type:
uinteger
minver:
3
definition:
Alpha Video Mode. Presence of this Element indicates that the BlockAdditional Element could contain Alpha data.
8.1.4.1.31.5. PixelWidth Element
name:
PixelWidth
path:
\Segment\Tracks\TrackEntry\Video\PixelWidth
id:
0xB0
minOccurs:
1
maxOccurs:
1
range:
not 0
type:
uinteger
definition:
Width of the encoded video frames in pixels.
8.1.4.1.31.6. PixelHeight Element
name:
PixelHeight
path:
\Segment\Tracks\TrackEntry\Video\PixelHeight
id:
0xBA
minOccurs:
1
maxOccurs:
1
range:
not 0
type:
uinteger
definition:
Height of the encoded video frames in pixels.
8.1.4.1.31.7. PixelCropBottom Element
name:
PixelCropBottom
path:
\Segment\Tracks\TrackEntry\Video\PixelCropBottom
id:
0x54AA
maxOccurs:
1
default:
0
type:
uinteger
definition:
The number of video pixels to remove at the bottom of the image.
8.1.4.1.31.8. PixelCropTop Element
name:
PixelCropTop
path:
\Segment\Tracks\TrackEntry\Video\PixelCropTop
id:
0x54BB
maxOccurs:
1
default:
0
type:
uinteger
definition:
The number of video pixels to remove at the top of the image.
8.1.4.1.31.9. PixelCropLeft Element
name:
PixelCropLeft
path:
\Segment\Tracks\TrackEntry\Video\PixelCropLeft
id:
0x54CC
maxOccurs:
1
default:
0
type:
uinteger
definition:
The number of video pixels to remove on the left of the image.
8.1.4.1.31.10. PixelCropRight Element
name:
PixelCropRight
path:
\Segment\Tracks\TrackEntry\Video\PixelCropRight
id:
0x54DD
maxOccurs:
1
default:
0
type:
uinteger
definition:
The number of video pixels to remove on the right of the image.
8.1.4.1.31.11. DisplayWidth Element
name:
DisplayWidth
path:
\Segment\Tracks\TrackEntry\Video\DisplayWidth
id:
0x54B0
maxOccurs:
1
range:
not 0

default: see implementation notes

type:
uinteger
definition:
Width of the video frames to display. Applies to the video frame after cropping (PixelCrop* Elements).

notes:

Table 8: DisplayWidth implementation notes
attribute note
default If the DisplayUnit of the same TrackEntry is 0, then the default value for DisplayWidth is equal toPixelWidth - PixelCropLeft - PixelCropRight, else there is no default value.
8.1.4.1.31.12. DisplayHeight Element
name:
DisplayHeight
path:
\Segment\Tracks\TrackEntry\Video\DisplayHeight
id:
0x54BA
maxOccurs:
1
range:
not 0

default: see implementation notes

type:
uinteger
definition:
Height of the video frames to display. Applies to the video frame after cropping (PixelCrop* Elements).

notes:

Table 9: DisplayHeight implementation notes
attribute note
default If the DisplayUnit of the same TrackEntry is 0, then the default value for DisplayHeight is equal toPixelHeight - PixelCropTop - PixelCropBottom, else there is no default value.
8.1.4.1.31.13. DisplayUnit Element
name:
DisplayUnit
path:
\Segment\Tracks\TrackEntry\Video\DisplayUnit
id:
0x54B2
minOccurs:
1
maxOccurs:
1
default:
0
type:
uinteger
definition:
How DisplayWidth & DisplayHeight are interpreted.

restrictions:

Table 10: DisplayUnit values
value label
0 pixels
1 centimeters
2 inches
3 display aspect ratio
4 unknown
8.1.4.1.31.14. ColourSpace Element
name:
ColourSpace
path:
\Segment\Tracks\TrackEntry\Video\ColourSpace
id:
0x2EB524

minOccurs: see implementation notes

maxOccurs:
1
type:
binary
definition:
Specify the pixel format used for the Track's data as a FourCC. This value is similar in scope to the biCompression value of AVI's BITMAPINFOHEADER.

notes:

Table 11: ColourSpace implementation notes
attribute note
minOccurs ColourSpace MUST be set (minOccurs=1) in TrackEntry, when the CodecID Element of the TrackEntry is set to "V_UNCOMPRESSED".
8.1.4.1.31.15. Colour Element
name:
Colour
path:
\Segment\Tracks\TrackEntry\Video\Colour
id:
0x55B0
maxOccurs:
1
type:
master
minver:
4
definition:
Settings describing the colour format.
8.1.4.1.31.16. MatrixCoefficients Element
name:
MatrixCoefficients
path:
\Segment\Tracks\TrackEntry\Video\Colour\MatrixCoefficients
id:
0x55B1
minOccurs:
1
maxOccurs:
1
default:
2
type:
uinteger
minver:
4
definition:
The Matrix Coefficients of the video used to derive luma and chroma values from red, green, and blue color primaries. For clarity, the value and meanings for MatrixCoefficients are adopted from Table 4 of ISO/IEC 23001-8:2016 or ITU-T H.273.

restrictions:

Table 12: MatrixCoefficients values
value label
0 Identity
1 ITU-R BT.709
2 unspecified
3 reserved
4 US FCC 73.682
5 ITU-R BT.470BG
6 SMPTE 170M
7 SMPTE 240M
8 YCoCg
9 BT2020 Non-constant Luminance
10 BT2020 Constant Luminance
11 SMPTE ST 2085
12 Chroma-derived Non-constant Luminance
13 Chroma-derived Constant Luminance
14 ITU-R BT.2100-0
8.1.4.1.31.17. BitsPerChannel Element
name:
BitsPerChannel
path:
\Segment\Tracks\TrackEntry\Video\Colour\BitsPerChannel
id:
0x55B2
maxOccurs:
1
default:
0
type:
uinteger
minver:
4
definition:
Number of decoded bits per channel. A value of 0 indicates that the BitsPerChannel is unspecified.
8.1.4.1.31.18. ChromaSubsamplingHorz Element
name:
ChromaSubsamplingHorz
path:
\Segment\Tracks\TrackEntry\Video\Colour\ChromaSubsamplingHorz
id:
0x55B3
maxOccurs:
1
type:
uinteger
minver:
4
definition:
The amount of pixels to remove in the Cr and Cb channels for every pixel not removed horizontally. Example: For video with 4:2:0 chroma subsampling, the ChromaSubsamplingHorz SHOULD be set to 1.
8.1.4.1.31.19. ChromaSubsamplingVert Element
name:
ChromaSubsamplingVert
path:
\Segment\Tracks\TrackEntry\Video\Colour\ChromaSubsamplingVert
id:
0x55B4
maxOccurs:
1
type:
uinteger
minver:
4
definition:
The amount of pixels to remove in the Cr and Cb channels for every pixel not removed vertically. Example: For video with 4:2:0 chroma subsampling, the ChromaSubsamplingVert SHOULD be set to 1.
8.1.4.1.31.20. CbSubsamplingHorz Element
name:
CbSubsamplingHorz
path:
\Segment\Tracks\TrackEntry\Video\Colour\CbSubsamplingHorz
id:
0x55B5
maxOccurs:
1
type:
uinteger
minver:
4
definition:
The amount of pixels to remove in the Cb channel for every pixel not removed horizontally. This is additive with ChromaSubsamplingHorz. Example: For video with 4:2:1 chroma subsampling, the ChromaSubsamplingHorz SHOULD be set to 1 and CbSubsamplingHorz SHOULD be set to 1.
8.1.4.1.31.21. CbSubsamplingVert Element
name:
CbSubsamplingVert
path:
\Segment\Tracks\TrackEntry\Video\Colour\CbSubsamplingVert
id:
0x55B6
maxOccurs:
1
type:
uinteger
minver:
4
definition:
The amount of pixels to remove in the Cb channel for every pixel not removed vertically. This is additive with ChromaSubsamplingVert.
8.1.4.1.31.22. ChromaSitingHorz Element
name:
ChromaSitingHorz
path:
\Segment\Tracks\TrackEntry\Video\Colour\ChromaSitingHorz
id:
0x55B7
minOccurs:
1
maxOccurs:
1
default:
0
type:
uinteger
minver:
4
definition:
How chroma is subsampled horizontally.

restrictions:

Table 13: ChromaSitingHorz values
value label
0 unspecified
1 left collocated
2 half
8.1.4.1.31.23. ChromaSitingVert Element
name:
ChromaSitingVert
path:
\Segment\Tracks\TrackEntry\Video\Colour\ChromaSitingVert
id:
0x55B8
minOccurs:
1
maxOccurs:
1
default:
0
type:
uinteger
minver:
4
definition:
How chroma is subsampled vertically.

restrictions:

Table 14: ChromaSitingVert values
value label
0 unspecified
1 top collocated
2 half
8.1.4.1.31.24. Range Element
name:
Range
path:
\Segment\Tracks\TrackEntry\Video\Colour\Range
id:
0x55B9
minOccurs:
1
maxOccurs:
1
default:
0
type:
uinteger
minver:
4
definition:
Clipping of the color ranges.

restrictions:

Table 15: Range values
value label
0 unspecified
1 broadcast range
2 full range (no clipping)
3 defined by MatrixCoefficients / TransferCharacteristics
8.1.4.1.31.25. TransferCharacteristics Element
name:
TransferCharacteristics
path:
\Segment\Tracks\TrackEntry\Video\Colour\TransferCharacteristics
id:
0x55BA
minOccurs:
1
maxOccurs:
1
default:
2
type:
uinteger
minver:
4
definition:
The transfer characteristics of the video. For clarity, the value and meanings for TransferCharacteristics are adopted from Table 3 of ISO/IEC 23091-4 or ITU-T H.273.

restrictions:

Table 16: TransferCharacteristics values
value label
0 reserved
1 ITU-R BT.709
2 unspecified
3 reserved
4 Gamma 2.2 curve - BT.470M
5 Gamma 2.8 curve - BT.470BG
6 SMPTE 170M
7 SMPTE 240M
8 Linear
9 Log
10 Log Sqrt
11 IEC 61966-2-4
12 ITU-R BT.1361 Extended Colour Gamut
13 IEC 61966-2-1
14 ITU-R BT.2020 10 bit
15 ITU-R BT.2020 12 bit
16 ITU-R BT.2100 Perceptual Quantization
17 SMPTE ST 428-1
18 ARIB STD-B67 (HLG)
8.1.4.1.31.26. Primaries Element
name:
Primaries
path:
\Segment\Tracks\TrackEntry\Video\Colour\Primaries
id:
0x55BB
minOccurs:
1
maxOccurs:
1
default:
2
type:
uinteger
minver:
4
definition:
The colour primaries of the video. For clarity, the value and meanings for Primaries are adopted from Table 2 of ISO/IEC 23091-4 or ITU-T H.273.

restrictions:

Table 17: Primaries values
value label
0 reserved
1 ITU-R BT.709
2 unspecified
3 reserved
4 ITU-R BT.470M
5 ITU-R BT.470BG - BT.601 625
6 ITU-R BT.601 525 - SMPTE 170M
7 SMPTE 240M
8 FILM
9 ITU-R BT.2020
10 SMPTE ST 428-1
11 SMPTE RP 432-2
12 SMPTE EG 432-2
22 EBU Tech. 3213-E - JEDEC P22 phosphors
8.1.4.1.31.27. MaxCLL Element
name:
MaxCLL
path:
\Segment\Tracks\TrackEntry\Video\Colour\MaxCLL
id:
0x55BC
maxOccurs:
1
type:
uinteger
minver:
4
definition:
Maximum brightness of a single pixel (Maximum Content Light Level) in candelas per square meter (cd/m2).
8.1.4.1.31.28. MaxFALL Element
name:
MaxFALL
path:
\Segment\Tracks\TrackEntry\Video\Colour\MaxFALL
id:
0x55BD
maxOccurs:
1
type:
uinteger
minver:
4
definition:
Maximum brightness of a single full frame (Maximum Frame-Average Light Level) in candelas per square meter (cd/m2).
8.1.4.1.31.29. MasteringMetadata Element
name:
MasteringMetadata
path:
\Segment\Tracks\TrackEntry\Video\Colour\MasteringMetadata
id:
0x55D0
maxOccurs:
1
type:
master
minver:
4
definition:
SMPTE 2086 mastering data.
8.1.4.1.31.30. PrimaryRChromaticityX Element
name:
PrimaryRChromaticityX
path:
\Segment\Tracks\TrackEntry\Video\Colour\MasteringMetadata\PrimaryRChromaticityX
id:
0x55D1
maxOccurs:
1
range:
0-1
type:
float
minver:
4
definition:
Red X chromaticity coordinate, as defined by CIE 1931.
8.1.4.1.31.31. PrimaryRChromaticityY Element
name:
PrimaryRChromaticityY
path:
\Segment\Tracks\TrackEntry\Video\Colour\MasteringMetadata\PrimaryRChromaticityY
id:
0x55D2
maxOccurs:
1
range:
0-1
type:
float
minver:
4
definition:
Red Y chromaticity coordinate, as defined by CIE 1931.
8.1.4.1.31.32. PrimaryGChromaticityX Element
name:
PrimaryGChromaticityX
path:
\Segment\Tracks\TrackEntry\Video\Colour\MasteringMetadata\PrimaryGChromaticityX
id:
0x55D3
maxOccurs:
1
range:
0-1
type:
float
minver:
4
definition:
Green X chromaticity coordinate, as defined by CIE 1931.
8.1.4.1.31.33. PrimaryGChromaticityY Element
name:
PrimaryGChromaticityY
path:
\Segment\Tracks\TrackEntry\Video\Colour\MasteringMetadata\PrimaryGChromaticityY
id:
0x55D4
maxOccurs:
1
range:
0-1
type:
float
minver:
4
definition:
Green Y chromaticity coordinate, as defined by CIE 1931.
8.1.4.1.31.34. PrimaryBChromaticityX Element
name:
PrimaryBChromaticityX
path:
\Segment\Tracks\TrackEntry\Video\Colour\MasteringMetadata\PrimaryBChromaticityX
id:
0x55D5
maxOccurs:
1
range:
0-1
type:
float
minver:
4
definition:
Blue X chromaticity coordinate, as defined by CIE 1931.
8.1.4.1.31.35. PrimaryBChromaticityY Element
name:
PrimaryBChromaticityY
path:
\Segment\Tracks\TrackEntry\Video\Colour\MasteringMetadata\PrimaryBChromaticityY
id:
0x55D6
maxOccurs:
1
range:
0-1
type:
float
minver:
4
definition:
Blue Y chromaticity coordinate, as defined by CIE 1931.
8.1.4.1.31.36. WhitePointChromaticityX Element
name:
WhitePointChromaticityX
path:
\Segment\Tracks\TrackEntry\Video\Colour\MasteringMetadata\WhitePointChromaticityX
id:
0x55D7
maxOccurs:
1
range:
0-1
type:
float
minver:
4
definition:
White X chromaticity coordinate, as defined by CIE 1931.
8.1.4.1.31.37. WhitePointChromaticityY Element
name:
WhitePointChromaticityY
path:
\Segment\Tracks\TrackEntry\Video\Colour\MasteringMetadata\WhitePointChromaticityY
id:
0x55D8
maxOccurs:
1
range:
0-1
type:
float
minver:
4
definition:
White Y chromaticity coordinate, as defined by CIE 1931.
8.1.4.1.31.38. LuminanceMax Element
name:
LuminanceMax
path:
\Segment\Tracks\TrackEntry\Video\Colour\MasteringMetadata\LuminanceMax
id:
0x55D9
maxOccurs:
1
range:
>= 0x0p+0
type:
float
minver:
4
definition:
Maximum luminance. Represented in candelas per square meter (cd/m2).
8.1.4.1.31.39. LuminanceMin Element
name:
LuminanceMin
path:
\Segment\Tracks\TrackEntry\Video\Colour\MasteringMetadata\LuminanceMin
id:
0x55DA
maxOccurs:
1
range:
>= 0x0p+0
type:
float
minver:
4
definition:
Minimum luminance. Represented in candelas per square meter (cd/m2).
8.1.4.1.31.40. Projection Element
name:
Projection
path:
\Segment\Tracks\TrackEntry\Video\Projection
id:
0x7670
maxOccurs:
1
type:
master
minver:
4
definition:
Describes the video projection details. Used to render spherical and VR videos.
8.1.4.1.31.41. ProjectionType Element
name:
ProjectionType
path:
\Segment\Tracks\TrackEntry\Video\Projection\ProjectionType
id:
0x7671
minOccurs:
1
maxOccurs:
1
default:
0
type:
uinteger
minver:
4
definition:
Describes the projection used for this video track.

restrictions:

Table 18: ProjectionType values
value label
0 rectangular
1 equirectangular
2 cubemap
3 mesh
8.1.4.1.31.42. ProjectionPrivate Element
name:
ProjectionPrivate
path:
\Segment\Tracks\TrackEntry\Video\Projection\ProjectionPrivate
id:
0x7672
maxOccurs:
1
type:
binary
minver:
4
definition:
Private data that only applies to a specific projection.
  • If ProjectionType equals 0 (Rectangular), then this element must not be present.
  • If ProjectionType equals 1 (Equirectangular), then this element must be present and contain the same binary data that would be stored inside an ISOBMFF Equirectangular Projection Box ('equi').
  • If ProjectionType equals 2 (Cubemap), then this element must be present and contain the same binary data that would be stored inside an ISOBMFF Cubemap Projection Box ('cbmp').
  • If ProjectionType equals 3 (Mesh), then this element must be present and contain the same binary data that would be stored inside an ISOBMFF Mesh Projection Box ('mshp').
usage notes:
ISOBMFF box size and fourcc fields are not included in the binary data, but the FullBox version and flag fields are. This is to avoid redundant framing information while preserving versioning and semantics between the two container formats.
8.1.4.1.31.43. ProjectionPoseYaw Element
name:
ProjectionPoseYaw
path:
\Segment\Tracks\TrackEntry\Video\Projection\ProjectionPoseYaw
id:
0x7673
minOccurs:
1
maxOccurs:
1
default:
0x0p+0
type:
float
minver:
4
definition:
Specifies a yaw rotation to the projection.

Value represents a clockwise rotation, in degrees, around the up vector. This rotation must be applied before any ProjectionPosePitch or ProjectionPoseRoll rotations. The value of this field should be in the -180 to 180 degree range.

8.1.4.1.31.44. ProjectionPosePitch Element
name:
ProjectionPosePitch
path:
\Segment\Tracks\TrackEntry\Video\Projection\ProjectionPosePitch
id:
0x7674
minOccurs:
1
maxOccurs:
1
default:
0x0p+0
type:
float
minver:
4
definition:
Specifies a pitch rotation to the projection.

Value represents a counter-clockwise rotation, in degrees, around the right vector. This rotation must be applied after the ProjectionPoseYaw rotation and before the ProjectionPoseRoll rotation. The value of this field should be in the -90 to 90 degree range.

8.1.4.1.31.45. ProjectionPoseRoll Element
name:
ProjectionPoseRoll
path:
\Segment\Tracks\TrackEntry\Video\Projection\ProjectionPoseRoll
id:
0x7675
minOccurs:
1
maxOccurs:
1
default:
0x0p+0
type:
float
minver:
4
definition:
Specifies a roll rotation to the projection.

Value represents a counter-clockwise rotation, in degrees, around the forward vector. This rotation must be applied after the ProjectionPoseYaw and ProjectionPosePitch rotations. The value of this field should be in the -180 to 180 degree range.

8.1.4.1.32. Audio Element
name:
Audio
path:
\Segment\Tracks\TrackEntry\Audio
id:
0xE1
maxOccurs:
1
type:
master
definition:
Audio settings.
8.1.4.1.32.1. SamplingFrequency Element
name:
SamplingFrequency
path:
\Segment\Tracks\TrackEntry\Audio\SamplingFrequency
id:
0xB5
minOccurs:
1
maxOccurs:
1
range:
> 0x0p+0
default:
0x1.f4p+12
type:
float
definition:
Sampling frequency in Hz.
8.1.4.1.32.2. OutputSamplingFrequency Element
name:
OutputSamplingFrequency
path:
\Segment\Tracks\TrackEntry\Audio\OutputSamplingFrequency
id:
0x78B5
maxOccurs:
1
range:
> 0x0p+0

default: see implementation notes

type:
float
definition:
Real output sampling frequency in Hz (used for SBR techniques).

notes:

Table 19: OutputSamplingFrequency implementation notes
attribute note
default The default value for OutputSamplingFrequency of the same TrackEntry is equal to the SamplingFrequency.
8.1.4.1.32.3. Channels Element
name:
Channels
path:
\Segment\Tracks\TrackEntry\Audio\Channels
id:
0x9F
minOccurs:
1
maxOccurs:
1
range:
not 0
default:
1
type:
uinteger
definition:
Numbers of channels in the track.
8.1.4.1.32.4. BitDepth Element
name:
BitDepth
path:
\Segment\Tracks\TrackEntry\Audio\BitDepth
id:
0x6264
maxOccurs:
1
range:
not 0
type:
uinteger
definition:
Bits per sample, mostly used for PCM.
8.1.4.1.33. TrackOperation Element
name:
TrackOperation
path:
\Segment\Tracks\TrackEntry\TrackOperation
id:
0xE2
maxOccurs:
1
type:
master
minver:
3
definition:
Operation that needs to be applied on tracks to create this virtual track. For more details look at Section 20.8.
8.1.4.1.33.1. TrackCombinePlanes Element
name:
TrackCombinePlanes
path:
\Segment\Tracks\TrackEntry\TrackOperation\TrackCombinePlanes
id:
0xE3
maxOccurs:
1
type:
master
minver:
3
definition:
Contains the list of all video plane tracks that need to be combined to create this 3D track
8.1.4.1.33.2. TrackPlane Element
name:
TrackPlane
path:
\Segment\Tracks\TrackEntry\TrackOperation\TrackCombinePlanes\TrackPlane
id:
0xE4
minOccurs:
1
type:
master
minver:
3
definition:
Contains a video plane track that need to be combined to create this 3D track
8.1.4.1.33.3. TrackPlaneUID Element
name:
TrackPlaneUID
path:
\Segment\Tracks\TrackEntry\TrackOperation\TrackCombinePlanes\TrackPlane\TrackPlaneUID
id:
0xE5
minOccurs:
1
maxOccurs:
1
range:
not 0
type:
uinteger
minver:
3
definition:
The trackUID number of the track representing the plane.
8.1.4.1.33.4. TrackPlaneType Element
name:
TrackPlaneType
path:
\Segment\Tracks\TrackEntry\TrackOperation\TrackCombinePlanes\TrackPlane\TrackPlaneType
id:
0xE6
minOccurs:
1
maxOccurs:
1
type:
uinteger
minver:
3
definition:
The kind of plane this track corresponds to.

restrictions:

Table 20: TrackPlaneType values
value label
0 left eye
1 right eye
2 background
8.1.4.1.33.5. TrackJoinBlocks Element
name:
TrackJoinBlocks
path:
\Segment\Tracks\TrackEntry\TrackOperation\TrackJoinBlocks
id:
0xE9
maxOccurs:
1
type:
master
minver:
3
definition:
Contains the list of all tracks whose Blocks need to be combined to create this virtual track
8.1.4.1.33.6. TrackJoinUID Element
name:
TrackJoinUID
path:
\Segment\Tracks\TrackEntry\TrackOperation\TrackJoinBlocks\TrackJoinUID
id:
0xED
minOccurs:
1
range:
not 0
type:
uinteger
minver:
3
definition:
The trackUID number of a track whose blocks are used to create this virtual track.
8.1.4.1.34. ContentEncodings Element
name:
ContentEncodings
path:
\Segment\Tracks\TrackEntry\ContentEncodings
id:
0x6D80
maxOccurs:
1
type:
master
definition:
Settings for several content encoding mechanisms like compression or encryption.
8.1.4.1.34.1. ContentEncoding Element
name:
ContentEncoding
path:
\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding
id:
0x6240
minOccurs:
1
type:
master
definition:
Settings for one content encoding like compression or encryption.
8.1.4.1.34.2. ContentEncodingOrder Element
name:
ContentEncodingOrder
path:
\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentEncodingOrder
id:
0x5031
minOccurs:
1
maxOccurs:
1
default:
0
type:
uinteger
definition:
Tells when this modification was used during encoding/muxing starting with 0 and counting upwards. The decoder/demuxer has to start with the highest order number it finds and work its way down. This value has to be unique over all ContentEncodingOrder Elements in the TrackEntry that contains this ContentEncodingOrder element.
8.1.4.1.34.3. ContentEncodingScope Element
name:
ContentEncodingScope
path:
\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentEncodingScope
id:
0x5032
minOccurs:
1
maxOccurs:
1
default:
1
type:
uinteger
definition:
A bit field that describes which Elements have been modified in this way. Values (big-endian) can be OR'ed.

restrictions:

Table 21: ContentEncodingScope values
value label
1 All frame contents, excluding lacing data
2 The track's private data
4 The next ContentEncoding (next ContentEncodingOrder. Either the data inside ContentCompression and/or ContentEncryption)
8.1.4.1.34.4. ContentEncodingType Element
name:
ContentEncodingType
path:
\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentEncodingType
id:
0x5033
minOccurs:
1
maxOccurs:
1
default:
0
type:
uinteger
definition:
A value describing what kind of transformation is applied.

restrictions:

Table 22: ContentEncodingType values
value label
0 Compression
1 Encryption
8.1.4.1.34.5. ContentCompression Element
name:
ContentCompression
path:
\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentCompression
id:
0x5034
maxOccurs:
1
type:
master
definition:
Settings describing the compression used. This Element MUST be present if the value of ContentEncodingType is 0 and absent otherwise. Each block MUST be decompressable even if no previous block is available in order not to prevent seeking.
8.1.4.1.34.6. ContentCompAlgo Element
name:
ContentCompAlgo
path:
\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentCompression\ContentCompAlgo
id:
0x4254
minOccurs:
1
maxOccurs:
1
default:
0
type:
uinteger
definition:
The compression algorithm used.

defined values:

Table 23: ContentCompAlgo values
value label definition
0 zlib zlib compression [RFC1950].
1 bzlib bzip2 compression [BZIP2].
2 lzo1x Lempel– (U+2013)Ziv– (U+2013)Oberhumer compression [LZO].
3 Header Stripping Octets in ContentCompSettings (Section 8.1.4.1.34.7) have been stripped from each frame.
8.1.4.1.34.7. ContentCompSettings Element
name:
ContentCompSettings
path:
\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentCompression\ContentCompSettings
id:
0x4255
maxOccurs:
1
type:
binary
definition:
Settings that might be needed by the decompressor. For Header Stripping (ContentCompAlgo=3), the bytes that were removed from the beginning of each frames of the track.
8.1.4.1.34.8. ContentEncryption Element
name:
ContentEncryption
path:
\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentEncryption
id:
0x5035
maxOccurs:
1
type:
master
definition:
Settings describing the encryption used. This Element MUST be present if the value of ContentEncodingType is 1 (encryption) and MUST be ignored otherwise.
8.1.4.1.34.9. ContentEncAlgo Element
name:
ContentEncAlgo
path:
\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentEncryption\ContentEncAlgo
id:
0x47E1
minOccurs:
1
maxOccurs:
1
default:
0
type:
uinteger
definition:
The encryption algorithm used. The value "0" means that the contents have not been encrypted.

defined values:

Table 24: ContentEncAlgo values
value label definition
0 Not encrypted
1 DES Data Encryption Standard (DES) [FIPS.46-3].
2 3DES Triple Data Encryption Algorithm [RFC1851].
3 Twofish Twofish Encryption Algorithm [Twofish].
4 Blowfish Blowfish Encryption Algorithm [Blowfish].
5 AES Advanced Encryption Standard (AES) [FIPS.197].
8.1.4.1.34.10. ContentEncKeyID Element
name:
ContentEncKeyID
path:
\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentEncryption\ContentEncKeyID
id:
0x47E2
maxOccurs:
1
type:
binary
definition:
For public key algorithms this is the ID of the public key the the data was encrypted with.
8.1.4.1.34.11. ContentEncAESSettings Element
name:
ContentEncAESSettings
path:
\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentEncryption\ContentEncAESSettings
id:
0x47E7
maxOccurs:
1
type:
master
minver:
4
definition:
Settings describing the encryption algorithm used. If ContentEncAlgo != 5 this MUST be ignored.
8.1.4.1.34.12. AESSettingsCipherMode Element
name:
AESSettingsCipherMode
path:
\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentEncryption\ContentEncAESSettings\AESSettingsCipherMode
id:
0x47E8
minOccurs:
1
maxOccurs:
1
type:
uinteger
minver:
4
definition:
The AES cipher mode used in the encryption.

restrictions:

Table 25: AESSettingsCipherMode values
value label
1 AES-CTR / Counter, NIST SP 800-38A
2 AES-CBC / Cipher Block Chaining, NIST SP 800-38A

8.1.5. Cues Element

name:
Cues
path:
\Segment\Cues
id:
0x1C53BB6B

minOccurs: see implementation notes

maxOccurs:
1
type:
master
definition:
A Top-Level Element to speed seeking access. All entries are local to the Segment.

notes:

Table 26: Cues implementation notes
attribute note
minOccurs This Element SHOULD be set when the Segment is not transmitted as a live stream (see #livestreaming).
8.1.5.1. CuePoint Element
name:
CuePoint
path:
\Segment\Cues\CuePoint
id:
0xBB
minOccurs:
1
type:
master
definition:
Contains all information relative to a seek point in the Segment.
8.1.5.1.1. CueTime Element
name:
CueTime
path:
\Segment\Cues\CuePoint\CueTime
id:
0xB3
minOccurs:
1
maxOccurs:
1
type:
uinteger
definition:
Absolute timestamp according to the Segment time base.
8.1.5.1.2. CueTrackPositions Element
name:
CueTrackPositions
path:
\Segment\Cues\CuePoint\CueTrackPositions
id:
0xB7
minOccurs:
1
type:
master
definition:
Contain positions for different tracks corresponding to the timestamp.
8.1.5.1.2.1. CueTrack Element
name:
CueTrack
path:
\Segment\Cues\CuePoint\CueTrackPositions\CueTrack
id:
0xF7
minOccurs:
1
maxOccurs:
1
range:
not 0
type:
uinteger
definition:
The track for which a position is given.
8.1.5.1.2.2. CueClusterPosition Element
name:
CueClusterPosition
path:
\Segment\Cues\CuePoint\CueTrackPositions\CueClusterPosition
id:
0xF1
minOccurs:
1
maxOccurs:
1
type:
uinteger
definition:
The Segment Position of the Cluster containing the associated Block.
8.1.5.1.2.3. CueRelativePosition Element
name:
CueRelativePosition
path:
\Segment\Cues\CuePoint\CueTrackPositions\CueRelativePosition
id:
0xF0
maxOccurs:
1
type:
uinteger
minver:
4
definition:
The relative position inside the Cluster of the referenced SimpleBlock or BlockGroup with 0 being the first possible position for an Element inside that Cluster.
8.1.5.1.2.4. CueDuration Element
name:
CueDuration
path:
\Segment\Cues\CuePoint\CueTrackPositions\CueDuration
id:
0xB2
maxOccurs:
1
type:
uinteger
minver:
4
definition:
The duration of the block according to the Segment time base. If missing the track's DefaultDuration does not apply and no duration information is available in terms of the cues.
8.1.5.1.2.5. CueBlockNumber Element
name:
CueBlockNumber
path:
\Segment\Cues\CuePoint\CueTrackPositions\CueBlockNumber
id:
0x5378
maxOccurs:
1
range:
not 0
type:
uinteger
definition:
Number of the Block in the specified Cluster.
8.1.5.1.2.6. CueCodecState Element
name:
CueCodecState
path:
\Segment\Cues\CuePoint\CueTrackPositions\CueCodecState
id:
0xEA
maxOccurs:
1
default:
0
type:
uinteger
minver:
2
definition:
The Segment Position of the Codec State corresponding to this Cue Element. 0 means that the data is taken from the initial Track Entry.
8.1.5.1.2.7. CueReference Element
name:
CueReference
path:
\Segment\Cues\CuePoint\CueTrackPositions\CueReference
id:
0xDB
type:
master
minver:
2
definition:
The Clusters containing the referenced Blocks.
8.1.5.1.2.8. CueRefTime Element
name:
CueRefTime
path:
\Segment\Cues\CuePoint\CueTrackPositions\CueReference\CueRefTime
id:
0x96
minOccurs:
1
maxOccurs:
1
type:
uinteger
minver:
2
definition:
Timestamp of the referenced Block.

8.1.6. Attachments Element

name:
Attachments
path:
\Segment\Attachments
id:
0x1941A469
maxOccurs:
1
type:
master
definition:
Contain attached files.
8.1.6.1. AttachedFile Element
name:
AttachedFile
path:
\Segment\Attachments\AttachedFile
id:
0x61A7
minOccurs:
1
type:
master
definition:
An attached file.
8.1.6.1.1. FileDescription Element
name:
FileDescription
path:
\Segment\Attachments\AttachedFile\FileDescription
id:
0x467E
maxOccurs:
1
type:
utf-8
definition:
A human-friendly name for the attached file.
8.1.6.1.2. FileName Element
name:
FileName
path:
\Segment\Attachments\AttachedFile\FileName
id:
0x466E
minOccurs:
1
maxOccurs:
1
type:
utf-8
definition:
Filename of the attached file.
8.1.6.1.3. FileMimeType Element
name:
FileMimeType
path:
\Segment\Attachments\AttachedFile\FileMimeType
id:
0x4660
minOccurs:
1
maxOccurs:
1
type:
string
definition:
MIME type of the file.
8.1.6.1.4. FileData Element
name:
FileData
path:
\Segment\Attachments\AttachedFile\FileData
id:
0x465C
minOccurs:
1
maxOccurs:
1
type:
binary
definition:
The data of the file.
8.1.6.1.5. FileUID Element
name:
FileUID
path:
\Segment\Attachments\AttachedFile\FileUID
id:
0x46AE
minOccurs:
1
maxOccurs:
1
range:
not 0
type:
uinteger
definition:
Unique ID representing the file, as random as possible.

8.1.7. Chapters Element

name:
Chapters
path:
\Segment\Chapters
id:
0x1043A770
maxOccurs:
1
type:
master
recurring:
1
definition:
A system to define basic menus and partition data. For more detailed information, look at the Chapters explanation in Section 22.
8.1.7.1. EditionEntry Element
name:
EditionEntry
path:
\Segment\Chapters\EditionEntry
id:
0x45B9
minOccurs:
1
type:
master
definition:
Contains all information about a Segment edition.
8.1.7.1.1. EditionUID Element
name:
EditionUID
path:
\Segment\Chapters\EditionEntry\EditionUID
id:
0x45BC
maxOccurs:
1
range:
not 0
type:
uinteger
definition:
A unique ID to identify the edition. It's useful for tagging an edition.
8.1.7.1.2. EditionFlagDefault Element
name:
EditionFlagDefault
path:
\Segment\Chapters\EditionEntry\EditionFlagDefault
id:
0x45DB
minOccurs:
1
maxOccurs:
1
range:
0-1
default:
0
type:
uinteger
definition:
Set to 1 if the edition SHOULD be used as the default one.
8.1.7.1.3. EditionFlagOrdered Element
name:
EditionFlagOrdered
path:
\Segment\Chapters\EditionEntry\EditionFlagOrdered
id:
0x45DD
minOccurs:
1
maxOccurs:
1
range:
0-1
default:
0
type:
uinteger
definition:
Set to 1 if the chapters can be defined multiple times and the order to play them is enforced; see Section 22.1.3.
8.1.7.1.4. ChapterAtom Element
name:
ChapterAtom
path:
\Segment\Chapters\EditionEntry\+ChapterAtom
id:
0xB6
minOccurs:
1
type:
master
recursive:
1
definition:
Contains the atom information to use as the chapter atom (apply to all tracks).
8.1.7.1.4.1. ChapterUID Element
name:
ChapterUID
path:
\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterUID
id:
0x73C4
minOccurs:
1
maxOccurs:
1
range:
not 0
type:
uinteger
definition:
A unique ID to identify the Chapter.
8.1.7.1.4.2. ChapterStringUID Element
name:
ChapterStringUID
path:
\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterStringUID
id:
0x5654
maxOccurs:
1
type:
utf-8
minver:
3
definition:
A unique string ID to identify the Chapter. Use for WebVTT cue identifier storage [WebVTT].
8.1.7.1.4.3. ChapterTimeStart Element
name:
ChapterTimeStart
path:
\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterTimeStart
id:
0x91
minOccurs:
1
maxOccurs:
1
type:
uinteger
definition:
Timestamp of the start of Chapter (not scaled).
8.1.7.1.4.4. ChapterTimeEnd Element
name:
ChapterTimeEnd
path:
\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterTimeEnd
id:
0x92
maxOccurs:
1
type:
uinteger
definition:
Timestamp of the end of Chapter (timestamp excluded, not scaled). The value MUST be strictly greater than the ChapterTimeStart of the same ChapterAtom.
usage notes:
If the Edition is an ordered edition, see Section 22.1.3, then this Element is REQUIRED.
8.1.7.1.4.5. ChapterFlagHidden Element
name:
ChapterFlagHidden
path:
\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterFlagHidden
id:
0x98
minOccurs:
1
maxOccurs:
1
range:
0-1
default:
0
type:
uinteger
definition:
Set to 1 if a chapter is hidden. Hidden chapters it SHOULD NOT be available to the user interface (but still to Control Tracks; see Section 22.2.3 on Chapter flags).
8.1.7.1.4.6. ChapterSegmentUID Element
name:
ChapterSegmentUID
path:
\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterSegmentUID
id:
0x6E67

minOccurs: see implementation notes

maxOccurs:
1
range:
>0
type:
binary
definition:
The SegmentUID of another Segment to play during this chapter.

notes:

Table 27: ChapterSegmentUID implementation notes
attribute note
minOccurs ChapterSegmentUID MUST be set (minOccurs=1) if ChapterSegmentEditionUID is used; see Section 19.2 on medium-linking Segments.
8.1.7.1.4.7. ChapterSegmentEditionUID Element
name:
ChapterSegmentEditionUID
path:
\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterSegmentEditionUID
id:
0x6EBC
maxOccurs:
1
range:
not 0
type:
uinteger
definition:
The EditionUID to play from the Segment linked in ChapterSegmentUID. If ChapterSegmentEditionUID is undeclared, then no Edition of the linked Segment is used; see Section 19.2 on medium-linking Segments.
8.1.7.1.4.8. ChapterPhysicalEquiv Element
name:
ChapterPhysicalEquiv
path:
\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterPhysicalEquiv
id:
0x63C3
maxOccurs:
1
type:
uinteger
definition:
Specify the physical equivalent of this ChapterAtom like "DVD" (60) or "SIDE" (50); see Section 22.4 for a complete list of values.
8.1.7.1.4.9. ChapterDisplay Element
name:
ChapterDisplay
path:
\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterDisplay
id:
0x80
type:
master
definition:
Contains all possible strings to use for the chapter display.
8.1.7.1.4.10. ChapString Element
name:
ChapString
path:
\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterDisplay\ChapString
id:
0x85
minOccurs:
1
maxOccurs:
1
type:
utf-8
definition:
Contains the string to use as the chapter atom.
8.1.7.1.4.11. ChapLanguage Element
name:
ChapLanguage
path:
\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterDisplay\ChapLanguage
id:
0x437C
minOccurs:
1
default:
eng
type:
string
definition:
A language corresponding to the string, in the bibliographic ISO-639-2 form [ISO639-2]. This Element MUST be ignored if a ChapLanguageIETF Element is used within the same ChapterDisplay Element.
8.1.7.1.4.12. ChapLanguageIETF Element
name:
ChapLanguageIETF
path:
\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterDisplay\ChapLanguageIETF
id:
0x437D
type:
string
minver:
4
definition:
Specifies a language corresponding to the ChapString in the format defined in [BCP47] and using the IANA Language Subtag Registry [IANALangRegistry]. If a ChapLanguageIETF Element is used, then any ChapLanguage and ChapCountry Elements used in the same ChapterDisplay MUST be ignored.
8.1.7.1.4.13. ChapCountry Element
name:
ChapCountry
path:
\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterDisplay\ChapCountry
id:
0x437E
type:
string
definition:
A country corresponding to the string, using the same 2 octets country-codes as in Internet domains [IANADomains] based on [ISO3166-1] alpha-2 codes. This Element MUST be ignored if a ChapLanguageIETF Element is used within the same ChapterDisplay Element.
8.1.7.1.4.14. ChapProcess Element
name:
ChapProcess
path:
\Segment\Chapters\EditionEntry\+ChapterAtom\ChapProcess
id:
0x6944
type:
master
definition:
Contains all the commands associated to the Atom.
8.1.7.1.4.15. ChapProcessCodecID Element
name:
ChapProcessCodecID
path:
\Segment\Chapters\EditionEntry\+ChapterAtom\ChapProcess\ChapProcessCodecID
id:
0x6955
minOccurs:
1
maxOccurs:
1
default:
0
type:
uinteger
definition:
Contains the type of the codec used for the processing. A value of 0 means native Matroska processing (to be defined), a value of 1 means the DVD command set is used; see Section 22.3 on DVD menus. More codec IDs can be added later.
8.1.7.1.4.16. ChapProcessPrivate Element
name:
ChapProcessPrivate
path:
\Segment\Chapters\EditionEntry\+ChapterAtom\ChapProcess\ChapProcessPrivate
id:
0x450D
maxOccurs:
1
type:
binary
definition:
Some optional data attached to the ChapProcessCodecID information. For ChapProcessCodecID = 1, it is the "DVD level" equivalent; see Section 22.3 on DVD menus.
8.1.7.1.4.17. ChapProcessCommand Element
name:
ChapProcessCommand
path:
\Segment\Chapters\EditionEntry\+ChapterAtom\ChapProcess\ChapProcessCommand
id:
0x6911
type:
master
definition:
Contains all the commands associated to the Atom.
8.1.7.1.4.18. ChapProcessTime Element
name:
ChapProcessTime
path:
\Segment\Chapters\EditionEntry\+ChapterAtom\ChapProcess\ChapProcessCommand\ChapProcessTime
id:
0x6922
minOccurs:
1
maxOccurs:
1
type:
uinteger
definition:
Defines when the process command SHOULD be handled

restrictions:

Table 28: ChapProcessTime values
value label
0 during the whole chapter
1 before starting playback
2 after playback of the chapter
8.1.7.1.4.19. ChapProcessData Element
name:
ChapProcessData
path:
\Segment\Chapters\EditionEntry\+ChapterAtom\ChapProcess\ChapProcessCommand\ChapProcessData
id:
0x6933
minOccurs:
1
maxOccurs:
1
type:
binary
definition:
Contains the command information. The data SHOULD be interpreted depending on the ChapProcessCodecID value. For ChapProcessCodecID = 1, the data correspond to the binary DVD cell pre/post commands; see Section 22.3 on DVD menus.

8.1.8. Tags Element

name:
Tags
path:
\Segment\Tags
id:
0x1254C367
type:
master
definition:
Element containing metadata describing Tracks, Editions, Chapters, Attachments, or the Segment as a whole. A list of valid tags can be found in [MatroskaTags].
8.1.8.1. Tag Element
name:
Tag
path:
\Segment\Tags\Tag
id:
0x7373
minOccurs:
1
type:
master
definition:
A single metadata descriptor.
8.1.8.1.1. Targets Element
name:
Targets
path:
\Segment\Tags\Tag\Targets
id:
0x63C0
minOccurs:
1
maxOccurs:
1
type:
master
definition:
Specifies which other elements the metadata represented by the Tag applies to. If empty or not present, then the Tag describes everything in the Segment.
8.1.8.1.1.1. TargetTypeValue Element
name:
TargetTypeValue
path:
\Segment\Tags\Tag\Targets\TargetTypeValue
id:
0x68CA
maxOccurs:
1
default:
50
type:
uinteger
definition:
A number to indicate the logical level of the target.

defined values:

Table 29: TargetTypeValue values
value label definition
70 COLLECTION The highest hierarchical level that tags can describe.
60 EDITION / ISSUE / VOLUME / OPUS / SEASON / SEQUEL A list of lower levels grouped together.
50 ALBUM / OPERA / CONCERT / MOVIE / EPISODE / CONCERT The most common grouping level of music and video (equals to an episode for TV series).
40 PART / SESSION When an album or episode has different logical parts.
30 TRACK / SONG / CHAPTER The common parts of an album or movie.
20 SUBTRACK / PART / MOVEMENT / SCENE Corresponds to parts of a track for audio (like a movement).
10 SHOT The lowest hierarchy found in music or movies.
8.1.8.1.1.2. TargetType Element
name:
TargetType
path:
\Segment\Tags\Tag\Targets\TargetType
id:
0x63CA
maxOccurs:
1
type:
string
definition:
An informational string that can be used to display the logical level of the target like "ALBUM", "TRACK", "MOVIE", "CHAPTER", etc ; see Section 6.4 of [MatroskaTags].

restrictions:

Table 30: TargetType values
value label
COLLECTION COLLECTION
EDITION EDITION
ISSUE ISSUE
VOLUME VOLUME
OPUS OPUS
SEASON SEASON
SEQUEL SEQUEL
ALBUM ALBUM
OPERA OPERA
CONCERT CONCERT
MOVIE MOVIE
EPISODE EPISODE
PART PART
SESSION SESSION
TRACK TRACK
SONG SONG
CHAPTER CHAPTER
SUBTRACK SUBTRACK
PART PART
MOVEMENT MOVEMENT
SCENE SCENE
SHOT SHOT
8.1.8.1.1.3. TagTrackUID Element
name:
TagTrackUID
path:
\Segment\Tags\Tag\Targets\TagTrackUID
id:
0x63C5
default:
0
type:
uinteger
definition:
A unique ID to identify the Track(s) the tags belong to.
usage notes:
If the value is 0 at this level, the tags apply to all tracks in the Segment. If set to any other value, it MUST match the TrackUID value of a track found in this Segment.
8.1.8.1.1.4. TagEditionUID Element
name:
TagEditionUID
path:
\Segment\Tags\Tag\Targets\TagEditionUID
id:
0x63C9
default:
0
type:
uinteger
definition:
A unique ID to identify the EditionEntry(s) the tags belong to.
usage notes:
If the value is 0 at this level, the tags apply to all editions in the Segment. If set to any other value, it MUST match the EditionUID value of an edition found in this Segment.
8.1.8.1.1.5. TagChapterUID Element
name:
TagChapterUID
path:
\Segment\Tags\Tag\Targets\TagChapterUID
id:
0x63C4
default:
0
type:
uinteger
definition:
A unique ID to identify the Chapter(s) the tags belong to.
usage notes:
If the value is 0 at this level, the tags apply to all chapters in the Segment. If set to any other value, it MUST match the ChapterUID value of a chapter found in this Segment.
8.1.8.1.1.6. TagAttachmentUID Element
name:
TagAttachmentUID
path:
\Segment\Tags\Tag\Targets\TagAttachmentUID
id:
0x63C6
default:
0
type:
uinteger
definition:
A unique ID to identify the Attachment(s) the tags belong to.
usage notes:
If the value is 0 at this level, the tags apply to all the attachments in the Segment. If set to any other value, it MUST match the FileUID value of an attachment found in this Segment.
8.1.8.1.2. SimpleTag Element
name:
SimpleTag
path:
\Segment\Tags\Tag\+SimpleTag
id:
0x67C8
minOccurs:
1
type:
master
recursive:
1
definition:
Contains general information about the target.
8.1.8.1.2.1. TagName Element
name:
TagName
path:
\Segment\Tags\Tag\+SimpleTag\TagName
id:
0x45A3
minOccurs:
1
maxOccurs:
1
type:
utf-8
definition:
The name of the Tag that is going to be stored.
8.1.8.1.2.2. TagLanguage Element
name:
TagLanguage
path:
\Segment\Tags\Tag\+SimpleTag\TagLanguage
id:
0x447A
minOccurs:
1
maxOccurs:
1
default:
und
type:
string
definition:
Specifies the language of the tag specified, in the Matroska languages form; see Section 6 on language codes. This Element MUST be ignored if the TagLanguageIETF Element is used within the same SimpleTag Element.
8.1.8.1.2.3. TagLanguageIETF Element
name:
TagLanguageIETF
path:
\Segment\Tags\Tag\+SimpleTag\TagLanguageIETF
id:
0x447B
maxOccurs:
1
type:
string
minver:
4
definition:
Specifies the language used in the TagString according to [BCP47] and using the IANA Language Subtag Registry [IANALangRegistry]. If this Element is used, then any TagLanguage Elements used in the same SimpleTag MUST be ignored.
8.1.8.1.2.4. TagDefault Element
name:
TagDefault
path:
\Segment\Tags\Tag\+SimpleTag\TagDefault
id:
0x4484
minOccurs:
1
maxOccurs:
1
range:
0-1
default:
1
type:
uinteger
definition:
A boolean value to indicate if this is the default/original language to use for the given tag.
8.1.8.1.2.5. TagString Element
name:
TagString
path:
\Segment\Tags\Tag\+SimpleTag\TagString
id:
0x4487
maxOccurs:
1
type:
utf-8
definition:
The value of the Tag.
8.1.8.1.2.6. TagBinary Element
name:
TagBinary
path:
\Segment\Tags\Tag\+SimpleTag\TagBinary
id:
0x4485
maxOccurs:
1
type:
binary
definition:
The values of the Tag, if it is binary. Note that this cannot be used in the same SimpleTag as TagString.

9. Matroska Element Ordering

Except for the EBML Header and the CRC-32 Element, the EBML specification does not require any particular storage order for Elements. The Matroska specification however defines mandates and recommendations for ordering certain Elements in order to facilitate better playback, seeking, and editing efficiency. This section describes and offers rationale for ordering requirements and recommendations for Matroska.

9.1. Top-Level Elements

The Info Element is the only REQUIRED Top-Level Element in a Matroska file. To be playable, Matroska MUST also contain at least one Tracks Element and Cluster Element. The first Info Element and the first Tracks Element MUST either be stored before the first Cluster Element or both SHALL be referenced by a SeekHead Element occurring before the first Cluster Element.

It is possible to edit a Matroska file after it has been created. For example, chapters, tags, or attachments can be added. When new Top-Level Elements are added to a Matroska file, the SeekHead Element(s) MUST be updated so that the SeekHead Element(s) itemize the identity and position of all Top-Level Elements. Editing, removing, or adding Elements to a Matroska file often requires that some existing Elements be voided or extended; therefore, it is RECOMMENDED to use Void Elements as padding in between Top-Level Elements.

9.2. CRC-32

As noted by the EBML specification, if a CRC-32 Element is used, then the CRC-32 Element MUST be the first ordered Element within its Parent Element. The Matroska specification recommends that CRC-32 Elements SHOULD NOT be used as an immediate Child Element of the Segment Element; however all Top-Level Elements of an EBML Document SHOULD include a CRC-32 Element as a Child Element.

9.3. SeekHead

If used, the first SeekHead Element SHOULD be the first non-CRC-32 Child Element of the Segment Element. If a second SeekHead Element is used, then the first SeekHead Element MUST reference the identity and position of the second SeekHead. Additionally, the second SeekHead Element MUST only reference Cluster Elements and not any other Top-Level Element already contained within the first SeekHead Element. The second SeekHead Element MAY be stored in any order relative to the other Top-Level Elements. Whether one or two SeekHead Element(s) are used, the SeekHead Element(s) MUST collectively reference the identity and position of all Top-Level Elements except for the first SeekHead Element.

It is RECOMMENDED that the first SeekHead Element be followed by a Void Element to allow for the SeekHead Element to be expanded to cover new Top-Level Elements that could be added to the Matroska file, such as Tags, Chapters, and Attachments Elements.

9.4. Cues (index)

The Cues Element is RECOMMENDED to optimize seeking access in Matroska. It is programmatically simpler to add the Cues Element after all Cluster Elements have been written because this does not require a prediction of how much space to reserve before writing the Cluster Elements. However, storing the Cues Element before the Cluster Elements can provide some seeking advantages. If the Cues Element is present, then it SHOULD either be stored before the first Cluster Element or be referenced by a SeekHead Element.

9.5. Info

The first Info Element SHOULD occur before the first Tracks Element and first Cluster Element except when referenced by a SeekHead Element.

9.6. Chapters Element

The Chapters Element SHOULD be placed before the Cluster Element(s). The Chapters Element can be used during playback even if the user does not need to seek. It immediately gives the user information about what section is being read and what other sections are available. In the case of Ordered Chapters it is RECOMMENDED to evaluate the logical linking even before playing. The Chapters Element SHOULD be placed before the first Tracks Element and after the first Info Element.

9.7. Attachments

The Attachments Element is not intended to be used by default when playing the file, but could contain information relevant to the content, such as cover art or fonts. Cover art is useful even before the file is played and fonts could be needed before playback starts for initialization of subtitles. The Attachments Element MAY be placed before the first Cluster Element; however if the Attachments Element is likely to be edited, then it SHOULD be placed after the last Cluster Element.

9.8. Tags

The Tags Element is most subject to changes after the file was originally created. For easier editing, the Tags Element SHOULD be placed at the end of the Segment Element, even after the Attachments Element. On the other hand, it is inconvenient to have to seek in the Segment for tags, especially for network streams. So it's better if the Tags Element is found early in the stream. When editing the Tags Element, the original Tags Element at the beginning can be overwritten with a Void Element and a new Tags Element written at the end of the Segment Element. The file size will only marginally change.

9.9. Optimum layout from a muxer

9.10. Optimum layout after editing tags

9.11. Optimum layout with Cues at the front

9.12. Cluster Timestamp

The Timestamp Element MUST occur as in storage order before any SimpleBlock, BlockGroup, or EncryptedBlock, within the Cluster Element.

10. Unknown elements

Matroska is based upon the principle that a reading application does not have to support 100% of the specifications in order to be able to play the file. A Matroska file therefore contains version indicators that tell a reading application what to expect.

It is possible and valid to have the version fields indicate that the file contains Matroska Elements from a higher specification version number while signaling that a reading application MUST only support a lower version number properly in order to play it back (possibly with a reduced feature set). For example, a reading application supporting at least Matroska version V reading a file whose DocTypeReadVersion field is equal to or lower than V MUST skip Matroska/EBML Elements it encounters but does not know about if that unknown element fits into the size constraints set by the current Parent Element.

11. DefaultDecodedFieldDuration

The DefaultDecodedFieldDuration Element can signal to the displaying application how often fields of a video sequence will be available for displaying. It can be used for both interlaced and progressive content. If the video sequence is signaled as interlaced, then the period between two successive fields at the output of the decoding process equals DefaultDecodedFieldDuration.

For video sequences signaled as progressive, it is twice the value of DefaultDecodedFieldDuration.

These values are valid at the end of the decoding process before post-processing (such as deinterlacing or inverse telecine) is applied.

Examples:

12. Block Structure

Bit 0 is the most significant bit.

Frames using references SHOULD be stored in "coding order". That means the references first, and then the frames referencing them. A consequence is that timestamps might not be consecutive. But a frame with a past timestamp MUST reference a frame already known, otherwise it's considered bad/void.

12.1. Block Header

Table 31: Block Header base parts
Offset Player Description
0x00+ MUST Track Number (Track Entry). It is coded in EBML like form (1 octet if the value is < 0x80, 2 if < 0x4000, etc) (most significant bits set to increase the range).
0x01+ MUST Timestamp (relative to Cluster timestamp, signed int16)

12.2. Block Header Flags

Table 32: Block Header flags part
Offset Bit Player Description
0x03+ 0-3 - Reserved, set to 0
0x03+ 4 - Invisible, the codec SHOULD decode this frame but not display it
0x03+ 5-6 MUST Lacing
* 00 : no lacing
* 01 : Xiph lacing
* 11 : EBML lacing
* 10 : fixed-size lacing
0x03+ 7 - not used

12.3. Lacing

Lacing is a mechanism to save space when storing data. It is typically used for small blocks of data (referred to as frames in Matroska). There are 3 types of lacing:

  1. Xiph, inspired by what is found in the Ogg container
  2. EBML, which is the same with sizes coded differently
  3. fixed-size, where the size is not coded

For example, a user wants to store 3 frames of the same track. The first frame is 800 octets long, the second is 500 octets long and the third is 1000 octets long. As these data are small, they can be stored in a lace to save space. They will then be stored in the same block as follows:

12.3.1. Xiph lacing

  • Block head (with lacing bits set to 01)
  • Lacing head: Number of frames in the lace -1 -- i.e. 2 (the 800 and 500 octets one)
  • Lacing sizes: only the 2 first ones will be coded, 800 gives 255;255;255;35, 500 gives 255;245. The size of the last frame is deduced from the total size of the Block.
  • Data in frame 1
  • Data in frame 2
  • Data in frame 3

A frame with a size multiple of 255 is coded with a 0 at the end of the size -- for example, 765 is coded 255;255;255;0.

12.3.2. EBML lacing

In this case, the size is not coded as blocks of 255 bytes, but as a difference with the previous size and this size is coded as in EBML. The first size in the lace is unsigned as in EBML. The others use a range shifting to get a sign on each value:

Table 33: EBML Lacing bits usage
Bit Representation Value
1xxx xxxx value -(26-1) to 26-1 (ie 0 to 27-2 minus 26-1, half of the range)
01xx xxxx xxxx xxxx value -(213-1) to 213-1
001x xxxx xxxx xxxx xxxx xxxx value -(220-1) to 220-1
0001 xxxx xxxx xxxx xxxx xxxx xxxx xxxx value -(227-1) to 227-1
0000 1xxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx value -(234-1) to 234-1
0000 01xx xxxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx value -(241-1) to 241-1
0000 001x xxxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx value -(248-1) to 248-1
  • Block head (with lacing bits set to 11)
  • Lacing head: Number of frames in the lace -1 -- i.e. 2 (the 800 and 500 octets one)
  • Lacing sizes: only the 2 first ones will be coded, 800 gives 0x320 0x4000 = 0x4320, 500 is coded as -300 : - 0x12C + 0x1FFF + 0x4000 = 0x5ED3. The size of the last frame is deduced from the total size of the Block.
  • Data in frame 1
  • Data in frame 2
  • Data in frame 3

12.3.3. Fixed-size lacing

In this case, only the number of frames in the lace is saved, the size of each frame is deduced from the total size of the Block. For example, for 3 frames of 800 octets each:

  • Block head (with lacing bits set to 10)
  • Lacing head: Number of frames in the lace -1 -- i.e. 2
  • Data in frame 1
  • Data in frame 2
  • Data in frame 3

12.4. SimpleBlock Structure

The SimpleBlock is inspired by the Block structure; see Section 12. The main differences are the added Keyframe flag and Discardable flag. Otherwise everything is the same.

Bit 0 is the most significant bit.

Frames using references SHOULD be stored in "coding order". That means the references first, and then the frames referencing them. A consequence is that timestamps might not be consecutive. But a frame with a past timestamp MUST reference a frame already known, otherwise it's considered bad/void.

12.4.1. SimpleBlock Header

Table 34: SimpleBlock Header base parts
Offset Player Description
0x00+ MUST Track Number (Track Entry). It is coded in EBML like form (1 octet if the value is < 0x80, 2 if < 0x4000, etc) (most significant bits set to increase the range).
0x01+ MUST Timestamp (relative to Cluster timestamp, signed int16)

12.4.2. SimpleBlock Header Flags

Table 35: SimpleBlock Header flags part
Offset Bit Player Description
0x03+ 0 - Keyframe, set when the Block contains only keyframes
0x03+ 1-3 - Reserved, set to 0
0x03+ 4 - Invisible, the codec SHOULD decode this frame but not display it
0x03+ 5-6 MUST Lacing
* 00 : no lacing
* 01 : Xiph lacing
* 11 : EBML lacing
* 10 : fixed-size lacing
0x03+ 7 - Discardable, the frames of the Block can be discarded during playing if needed

12.4.3. Laced Data

When lacing bit is set.

Table 36: Lace sizes coded in the Block
Offset Player Description
0x00 MUST Number of frames in the lace-1 (uint8)
0x01 / 0xXX MUST Lace-coded size of each frame of the lace, except for the last one (multiple uint8). *This is not used with Fixed-size lacing as it is calculated automatically from (total size of lace) / (number of frames in lace).

For (possibly) Laced Data

Table 37: Lace data after lace sizes
Offset Player Description
0x00 MUST Consecutive laced frames

13. Timestamps

Historically timestamps in Matroska were mistakenly called timecodes. The Timestamp Element was called Timecode, the TimestampScale Element was called TimecodeScale, the TrackTimestampScale Element was called TrackTimecodeScale and the ReferenceTimestamp Element was called ReferenceTimeCode.

13.1. Timestamp Types

  • Absolute Timestamp = Block+Cluster
  • Relative Timestamp = Block
  • Scaled Timestamp = Block+Cluster
  • Raw Timestamp = (Block+Cluster)*TimestampScale*TrackTimestampScale

13.2. Block Timestamps

The Block Element's timestamp MUST be a signed integer that represents the Raw Timestamp relative to the Cluster's Timestamp Element, multiplied by the TimestampScale Element. See Section 13.4 for more information.

The Block Element's timestamp MUST be represented by a 16bit signed integer (sint16). The Block's timestamp has a range of -32768 to +32767 units. When using the default value of the TimestampScale Element, each integer represents 1ms. The maximum time span of Block Elements in a Cluster using the default TimestampScale Element of 1ms is 65536ms.

If a Cluster's Timestamp Element is set to zero, it is possible to have Block Elements with a negative Raw Timestamp. Block Elements with a negative Raw Timestamp are not valid.

13.3. Raw Timestamp

The exact time of an object SHOULD be represented in nanoseconds. To find out a Block's Raw Timestamp, you need the Block's Timestamp Element, the Cluster's Timestamp Element, and the TimestampScale Element.

13.4. TimestampScale

The TimestampScale Element is used to calculate the Raw Timestamp of a Block. The timestamp is obtained by adding the Block's timestamp to the Cluster's Timestamp Element, and then multiplying that result by the TimestampScale. The result will be the Block's Raw Timestamp in nanoseconds. The formula for this would look like:

(a + b) * c

a = `Block`'s Timestamp
b = `Cluster`'s Timestamp
c = `TimestampScale`

For example, assume a Cluster's Timestamp has a value of 564264, the Block has a Timestamp of 1233, and the TimestampScale Element is the default of 1000000.

(1233 + 564264) * 1000000 = 565497000000

So, the Block in this example has a specific time of 565497000000 in nanoseconds. In milliseconds this would be 565497ms.

13.5. TimestampScale Rounding

Because the default value of TimestampScale is 1000000, which makes each integer in the Cluster and Block Timestamp Elements equal 1ms, this is the most commonly used. When dealing with audio, this causes inaccuracy when seeking. When the audio is combined with video, this is not an issue. For most cases, the the synch of audio to video does not need to be more than 1ms accurate. This becomes obvious when one considers that sound will take 2-3ms to travel a single meter, so distance from your speakers will have a greater effect on audio/visual synch than this.

However, when dealing with audio-only files, seeking accuracy can become critical. For instance, when storing a whole CD in a single track, a user will want to be able to seek to the exact sample that a song begins at. If seeking a few sample ahead or behind, a crack or pop may result as a few odd samples are rendered. Also, when performing precise editing, it may be very useful to have the audio accuracy down to a single sample.

When storing timestamps for an audio stream, the TimestampScale Element SHOULD have an accuracy of at least that of the audio sample rate, otherwise there are rounding errors that prevent users from knowing the precise location of a sample. Here's how a program has to round each timestamp in order to be able to recreate the sample number accurately.

Let's assume that the application has an audio track with a sample rate of 44100. As written above the TimestampScale MUST have at least the accuracy of the sample rate itself: 1000000000 / 44100 = 22675.7369614512. This value MUST always be truncated. Otherwise the accuracy will not suffice. So in this example the application will use 22675 for the TimestampScale. The application could even use some lower value like 22674, which would allow it to be a little bit imprecise about the original timestamps. But more about that in a minute.

Next the application wants to write sample number 52340 and calculates the timestamp. This is easy. In order to calculate the Raw Timestamp in ns all it has to do is calculate Raw Timestamp = round(1000000000 * sample_number / sample_rate). Rounding at this stage is very important! The application might skip it if it choses a slightly smaller value for the TimestampScale factor instead of the truncated one like shown above. Otherwise it has to round or the results won't be reversible. For our example we get Raw Timestamp = round(1000000000 * 52340 / 44100) = round(1186848072.56236) = 1186848073.

The next step is to calculate the Absolute Timestamp - that is the timestamp that will be stored in the Matroska file. Here the application has to divide the Raw Timestamp from the previous paragraph by the TimestampScale factor and round the result: Absolute Timestamp = round(Raw Timestamp / TimestampScale_factor), which will result in the following for our example: Absolute Timestamp = round(1186848073 / 22675) = round(52341.7011245866) = 52342. This number is the one the application has to write to the file.

Now our file is complete, and we want to play it back with another application. Its task is to find out which sample the first application wrote into the file. So it starts reading the Matroska file and finds the TimestampScale factor 22675 and the audio sample rate 44100. Later it finds a data block with the Absolute Timestamp of 52342. But how does it get the sample number from these numbers?

First it has to calculate the Raw Timestamp of the block it has just read. Here's no rounding involved, just an integer multiplication: Raw Timestamp = Absolute Timestamp * TimestampScale_factor. In our example: Raw Timestamp = 52342 * 22675 = 1186854850.

The conversion from the Raw Timestamp to the sample number again requires rounding: sample_number = round(Raw Timestamp * sample_rate / 1000000000). In our example: sample_number = round(1186854850 * 44100 / 1000000000) = round(52340.298885) = 52340. This is exactly the sample number that the previous program started with.

Some general notes for a program:

  1. Always calculate the timestamps / sample numbers with floating point numbers of at least 64bit precision (called 'double' in most modern programming languages). If you're calculating with integers, then make sure they're 64bit long, too.
  2. Always round if you divide. Always! If you don't you'll end up with situations in which you have a timestamp in the Matroska file that does not correspond to the sample number that it started with. Using a slightly lower timestamp scale factor can help here in that it removes the need for proper rounding in the conversion from sample number to Raw Timestamp.

13.6. TrackTimestampScale

The TrackTimestampScale Element is used align tracks that would otherwise be played at different speeds. An example of this would be if you have a film that was originally recorded at 24fps video. When playing this back through a PAL broadcasting system, it is standard to speed up the film to 25fps to match the 25fps display speed of the PAL broadcasting standard. However, when broadcasting the video through NTSC, it is typical to leave the film at its original speed. If you wanted to make a single file where there was one video stream, and an audio stream used from the PAL broadcast, as well as an audio stream used from the NTSC broadcast, you would have the problem that the PAL audio stream would be 1/24th faster than the NTSC audio stream, quickly leading to problems. It is possible to stretch out the PAL audio track and re-encode it at a slower speed, however when dealing with lossy audio codecs, this often results in a loss of audio quality and/or larger file sizes.

This is the type of problem that TrackTimestampScale was designed to fix. Using it, the video can be played back at a speed that will synch with either the NTSC or the PAL audio stream, depending on which is being used for playback. To continue the above example:

Track 1: Video
Track 2: NTSC Audio
Track 3: PAL Audio

Because the NTSC track is at the original speed, it will used as the default value of 1.0 for its TrackTimestampScale. The video will also be aligned to the NTSC track with the default value of 1.0.

The TrackTimestampScale value to use for the PAL track would be calculated by determining how much faster the PAL track is than the NTSC track. In this case, because we know the video for the NTSC audio is being played back at 24fps and the video for the PAL audio is being played back at 25fps, the calculation would be:

25/24 is almost 1.04166666666666666667

When writing a file that uses a non-default TrackTimestampScale, the values of the Block's timestamp are whatever they would be when normally storing the track with a default value for the TrackTimestampScale. However, the data is interleaved a little differently. Data SHOULD be interleaved by its Raw Timestamp, see Section 13.3, in the order handed back from the encoder. The Raw Timestamp of a Block from a track using TrackTimestampScale is calculated using:

(Block's Timestamp + Cluster's Timestamp) * TimestampScale * TrackTimestampScale

So, a Block from the PAL track above that had a Scaled Timestamp, see Section 13.1, of 100 seconds would have a Raw Timestamp of 104.66666667 seconds, and so would be stored in that part of the file.

When playing back a track using the TrackTimestampScale, if the track is being played by itself, there is no need to scale it. From the above example, when playing the Video with the NTSC Audio, neither are scaled. However, when playing back the Video with the PAL Audio, the timestamps from the PAL Audio track are scaled using the TrackTimestampScale, resulting in the video playing back in synch with the audio.

It would be possible for a Matroska Player to also adjust the audio's samplerate at the same time as adjusting the timestamps if you wanted to play the two audio streams synchronously. It would also be possible to adjust the video to match the audio's speed. However, for playback, the selected track(s) timestamps SHOULD be adjusted if they need to be scaled.

While the above example deals specifically with audio tracks, this element can be used to align video, audio, subtitles, or any other type of track contained in a Matroska file.

14. Encryption

Encryption in Matroska is designed in a very generic style to allow people to implement whatever form of encryption is best for them. It is possible to use the encryption framework in Matroska as a type of DRM (Digital Rights Management).

Because encryption occurs within the Block Element, it is possible to manipulate encrypted streams without decrypting them. The streams could potentially be copied, deleted, cut, appended, or any number of other possible editing techniques without decryption. The data can be used without having to expose it or go through the decrypting process.

Encryption can also be layered within Matroska. This means that two completely different types of encryption can be used, requiring two separate keys to be able to decrypt a stream.

Encryption information is stored in the ContentEncodings Element under the ContentEncryption Element.

15. Image Presentation

15.1. Cropping

The PixelCrop Elements (PixelCropTop, PixelCropBottom, PixelCropRight, and PixelCropLeft) indicate when, and by how much, encoded videos frames SHOULD be cropped for display. These Elements allow edges of the frame that are not intended for display, such as the sprockets of a full-frame film scan or the VANC area of a digitized analog videotape, to be stored but hidden. PixelCropTop and PixelCropBottom store an integer of how many rows of pixels SHOULD be cropped from the top and bottom of the image (respectively). PixelCropLeft and PixelCropRight store an integer of how many columns of pixels SHOULD be cropped from the left and right of the image (respectively). For example, a pillar-boxed video that stores a 1440x1080 visual image within the center of a padded 1920x1080 encoded image MAY set both PixelCropLeft and PixelCropRight to "240", so that a Matroska Player SHOULD crop off 240 columns of pixels from the left and right of the encoded image to present the image with the pillar-boxes hidden.

15.2. Rotation

The ProjectionPoseRoll Element (see Section 8.1.4.1.31.45) can be used to indicate that the image from the associated video track SHOULD be rotated for presentation. For instance, the following representation of the Projection Element Section 8.1.4.1.31.40) and the ProjectionPoseRoll Element represents a video track where the image SHOULD be presentation with a 90 degree counter-clockwise rotation.

<Projection>
  <ProjectionPoseRoll>90</ProjectionPoseRoll>
</Projection>
Figure 11: Rotation example.

16. Matroska versioning

The EBML Header of each Matroska document informs the reading application on what version of Matroska to expect. The Elements within EBML Header with jurisdiction over this information are DocTypeVersion and DocTypeReadVersion.

DocTypeVersion MUST be equal to or greater than the highest Matroska version number of any Element present in the Matroska file. For example, a file using the SimpleBlock Element MUST have a DocTypeVersion equal to or greater than 2. A file containing CueRelativePosition Elements MUST have a DocTypeVersion equal to or greater than 4.

The DocTypeReadVersion MUST contain the minimum version number that a reading application can minimally support in order to play the file back -- optionally with a reduced feature set. For example, if a file contains only Elements of version 2 or lower except for CueRelativePosition (which is a version 4 Matroska Element), then DocTypeReadVersion SHOULD still be set to 2 and not 4 because evaluating CueRelativePosition is not necessary for standard playback -- it makes seeking more precise if used.

DocTypeVersion MUST always be equal to or greater than DocTypeReadVersion.

A reading application supporting Matroska version V MUST NOT refuse to read an application with DocReadTypeVersion equal to or lower than V even if DocTypeVersion is greater than V. See also the note about Unknown Elements in Section 10.

17. MIME Types

There is no IETF endorsed MIME type for Matroska files. These definitions can be used:

18. Segment Position

The Segment Position of an Element refers to the position of the first octet of the Element ID of that Element, measured in octets, from the beginning of the Element Data section of the containing Segment Element. In other words, the Segment Position of an Element is the distance in octets from the beginning of its containing Segment Element minus the size of the Element ID and Element Data Size of that Segment Element. The Segment Position of the first Child Element of the Segment Element is 0. An Element which is not stored within a Segment Element, such as the Elements of the EBML Header, do not have a Segment Position.

18.1. Segment Position Exception

Elements that are defined to store a Segment Position MAY define reserved values to indicate a special meaning.

18.2. Example of Segment Position

This table presents an example of Segment Position by showing a hexadecimal representation of a very small Matroska file with labels to show the offsets in octets. The file contains a Segment Element with an Element ID of "0x18538067" and a MuxingApp Element with an Element ID of "0x4D80".

     0                             1                             2
     0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5  6  7  8  9  0
     +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
   0 |1A|45|DF|A3|8B|42|82|88|6D|61|74|72|6F|73|6B|61|18|53|80|67|
  20 |93|15|49|A9|66|8E|4D|80|84|69|65|74|66|57|41|84|69|65|74|66|

In the above example, the Element ID of the Segment Element is stored at offset 16, the Element Data Size of the Segment Element is stored at offset 20, and the Element Data of the Segment Element is stored at offset 21.

The MuxingApp Element is stored at offset 26. Since the Segment Position of an Element is calculated by subtracting the position of the Element Data of the containing Segment Element from the position of that Element, the Segment Position of MuxingApp Element in the above example is '26 - 21' or '5'.

19. Linked Segments

Matroska provides several methods to link two or many Segment Elements together to create a Linked Segment. A Linked Segment is a set of multiple Segments related together into a single presentation by using Hard Linking, Medium Linking, or Soft Linking. All Segments within a Linked Segment MUST utilize the same track numbers and timescale. All Segments within a Linked Segment MUST be stored within the same directory. All Segments within a Linked Segment MUST store a SegmentUID.

19.1. Hard Linking

Hard Linking (also called splitting) is the process of creating a Linked Segment by relating multiple Segment Elements using the NextUID and PrevUID Elements. Within a Linked Segment, the timestamps of each Segment MUST follow consecutively in linking order. With Hard Linking, the chapters of any Segment within the Linked Segment MUST only reference the current Segment. With Hard Linking, the NextUID and PrevUID MUST reference the respective SegmentUID values of the next and previous Segments. The first Segment of a Linked Segment SHOULD have a NextUID Element and MUST NOT have a PrevUID Element. The last Segment of a Linked Segment SHOULD have a PrevUID Element and MUST NOT have a NextUID Element. The middle Segments of a Linked Segment SHOULD have both a NextUID Element and a PrevUID Element.

In a chain of Linked Segments the NextUID always takes precedence over the PrevUID. So if SegmentA has a NextUID to SegmentB and SegmentB has a PrevUID to SegmentC, the link to use is SegmentA to SegmentB. If SegmentB has a PrevUID to SegmentA but SegmentA has no NextUID, then the Matroska Player MAY consider these two Segments linked as SegmentA followed by SegmentB.

As an example, three Segments can be Hard Linked as a Linked Segment through cross-referencing each other with SegmentUID, PrevUID, and NextUID, as in this table.

Table 38: Usual Hard Linking UIDs
file name SegmentUID PrevUID NextUID
start.mkv 71000c23cd310998 53fbc94dd984a5dd n/a a77b3598941cb803 eac0fcdafe44fac9
middle.mkv a77b3598941cb803 eac0fcdafe44fac9 71000c23cd310998 53fbc94dd984a5dd 6c92285fa6d3e827 b198d120ea3ac674
end.mkv 6c92285fa6d3e827 b198d120ea3ac674 a77b3598941cb803 eac0fcdafe44fac9 n/a

An other example where only the NextUID Element is used.

Table 39: Hard Linking without PrevUID
file name SegmentUID PrevUID NextUID
start.mkv 71000c23cd310998 53fbc94dd984a5dd n/a a77b3598941cb803 eac0fcdafe44fac9
middle.mkv a77b3598941cb803 eac0fcdafe44fac9 n/a 6c92285fa6d3e827 b198d120ea3ac674
end.mkv 6c92285fa6d3e827 b198d120ea3ac674 n/a n/a

A next example where only the PrevUID Element is used.

Table 40: Hard Linking without NextUID
file name SegmentUID PrevUID NextUID
start.mkv 71000c23cd310998 53fbc94dd984a5dd n/a n/a
middle.mkv a77b3598941cb803 eac0fcdafe44fac9 71000c23cd310998 53fbc94dd984a5dd n/a
end.mkv 6c92285fa6d3e827 b198d120ea3ac674 a77b3598941cb803 eac0fcdafe44fac9 n/a

In this example only the middle.mkv is using the PrevUID and NextUID Elements.

Table 41: Hard Linking with mixed UID links
file name SegmentUID PrevUID NextUID
start.mkv 71000c23cd310998 53fbc94dd984a5dd n/a n/a
middle.mkv a77b3598941cb803 eac0fcdafe44fac9 71000c23cd310998 53fbc94dd984a5dd 6c92285fa6d3e827 b198d120ea3ac674
end.mkv 6c92285fa6d3e827 b198d120ea3ac674 n/a n/a

19.2. Medium Linking

Medium Linking creates relationships between Segments using Ordered Chapters and the ChapterSegmentUID Element. A Segment Edition with Ordered Chapters MAY contain Chapter elements that reference timestamp ranges from other Segments. The Segment referenced by the Ordered Chapter via the ChapterSegmentUID Element SHOULD be played as part of a Linked Segment. The timestamps of Segment content referenced by Ordered Chapters MUST be adjusted according to the cumulative duration of the the previous Ordered Chapters.

As an example a file named intro.mkv could have a SegmentUID of "0xb16a58609fc7e60653a60c984fc11ead". Another file called program.mkv could use a Chapter Edition that contains two Ordered Chapters. The first chapter references the Segment of intro.mkv with the use of a ChapterSegmentUID, ChapterSegmentEditionUID, ChapterTimeStart, and optionally a ChapterTimeEnd element. The second chapter references content within the Segment of program.mkv. A Matroska Player SHOULD recognize the Linked Segment created by the use of ChapterSegmentUID in an enabled Edition and present the reference content of the two Segments together.

The ChapterSegmentUID is a binary value and the base element to set up a Linked Chapter in 2 variations: the Linked-Duration linking and the Linked-Edition linking. For both variations, the following 3 conditions MUST be met:

  1. The EditionFlagOrdered Flag MUST be true.
  2. The ChapterSegmentUID MUST NOT be the SegmentUID of its own Segment.
  3. The linked Segments MUST BE in the same folder.

19.2.1. Variation 1: Linked-Duration

Two more conditions MUST be met:

  1. ChapterTimeStart and ChapterTimeEnd timestamps MUST be in the range of the linked Segment duration.
  2. ChapterSegmentEditionUID MUST NOT be set.

A Matroska Player MUST play the content of the linked Segment from the ChapterTimeStart until ChapterTimeEnd timestamp.

19.2.2. Variation 2: Linked-Edition

When the ChapterSegmentEditionUID is set to a valid EditionUID from the linked Segment. A Matroska Player MUST play these linked Edition.

19.3. Soft Linking

Soft Linking is used by codec chapters. They can reference another Segment and jump to that Segment. The way the Segments are described are internal to the chapter codec and unknown to the Matroska level. But there are Elements within the Info Element (such as ChapterTranslate) that can translate a value representing a Segment in the chapter codec and to the current SegmentUID. All Segments that could be used in a Linked Segment in this way SHOULD be marked as members of the same family via the SegmentFamily Element, so that the Matroska Player can quickly switch from one to the other.

20. Track Flags

20.1. Default flag

The "default track" flag is a hint for a Matroska Player indicating that a given track SHOULD be eligible to be automatically selected as the default track for a given language. If no tracks in a given language have the default track flag set, then all tracks in that language are eligible for automatic selection. This can be used to indicate that a track provides "regular service" suitable for users with default settings, as opposed to specialized services, such as commentary, hearing-impaired captions, or descriptive audio.

The Matroska Player MAY override the "default track" flag for any reason, including user preferences to prefer tracks providing accessibility services.

20.2. Forced flag

The "forced" flag tells the Matroska Player that it SHOULD display this subtitle track, even if user preferences usually would not call for any subtitles to be displayed alongside the current selected audio track. This can be used to indicate that a track contains translations of onscreen text, or of dialogue spoken in a different language than the track's primary one.

20.3. Hearing-impaired flag

The "hearing impaired" flag tells the Matroska Player that it SHOULD prefer this track when selecting a default track for a hearing-impaired user, and that it MAY prefer to select a different track when selecting a default track for a non-hearing-impaired user.

20.4. Visual-impaired flag

The "visual impaired" flag tells the Matroska Player that it SHOULD prefer this track when selecting a default track for a visually-impaired user, and that it MAY prefer to select a different track when selecting a default track for a non-visually-impaired user.

20.5. Descriptions flag

The "descriptions" flag tells the Matroska Player that this track is suitable to play via a text-to-speech system for a visually-impaired user, and that it SHOULD NOT automatically select this track when selecting a default track for a non-visually-impaired user.

20.6. Original flag

The "original" flag tells the Matroska Player that this track is in the original language, and that it SHOULD prefer it if configured to prefer original-language tracks of this track's type.

20.7. Commentary flag

The "commentary" flag tells the Matroska Player that this track contains commentary on the content.

20.8. Track Operation

TrackOperation allows combining multiple tracks to make a virtual one. It uses two separate system to combine tracks. One to create a 3D "composition" (left/right/background planes) and one to simplify join two tracks together to make a single track.

A track created with TrackOperation is a proper track with a UID and all its flags. However the codec ID is meaningless because each "sub" track needs to be decoded by its own decoder before the "operation" is applied. The Cues Elements corresponding to such a virtual track SHOULD be the sum of the Cues Elements for each of the tracks it's composed of (when the Cues are defined per track).

In the case of TrackJoinBlocks, the Block Elements (from BlockGroup and SimpleBlock) of all the tracks SHOULD be used as if they were defined for this new virtual Track. When two Block Elements have overlapping start or end timestamps, it's up to the underlying system to either drop some of these frames or render them the way they overlap. This situation SHOULD be avoided when creating such tracks as you can never be sure of the end result on different platforms.

20.9. Overlay Track

Overlay tracks SHOULD be rendered in the same channel as the track its linked to. When content is found in such a track, it SHOULD be played on the rendering channel instead of the original track.

20.10. Multi-planar and 3D videos

There are two different ways to compress 3D videos: have each eye track in a separate track and have one track have both eyes combined inside (which is more efficient, compression-wise). Matroska supports both ways.

For the single track variant, there is the StereoMode Element, which defines how planes are assembled in the track (mono or left-right combined). Odd values of StereoMode means the left plane comes first for more convenient reading. The pixel count of the track (PixelWidth/PixelHeight) is the raw amount of pixels, for example 3840x1080 for full HD side by side, and the DisplayWidth/DisplayHeight in pixels is the amount of pixels for one plane (1920x1080 for that full HD stream). Old stereo 3D were displayed using anaglyph (cyan and red colors separated). For compatibility with such movies, there is a value of the StereoMode that corresponds to AnaGlyph.

There is also a "packed" mode (values 13 and 14) which consists of packing two frames together in a Block using lacing. The first frame is the left eye and the other frame is the right eye (or vice versa). The frames SHOULD be decoded in that order and are possibly dependent on each other (P and B frames).

For separate tracks, Matroska needs to define exactly which track does what. TrackOperation with TrackCombinePlanes do that. For more details look at Section 20.8 on how TrackOperation works.

The 3D support is still in infancy and may evolve to support more features.

The StereoMode used to be part of Matroska v2 but it didn't meet the requirement for multiple tracks. There was also a bug in libmatroska prior to 0.9.0 that would save/read it as 0x53B9 instead of 0x53B8. Matroska Readers may support these legacy files by checking Matroska v2 or 0x53B9. The older values were 0: mono, 1: right eye, 2: left eye, 3: both eyes.

21. Default track selection

This section provides some example sets of Tracks and hypothetical user settings, along with indications of which ones a similarly-configured Matroska Player SHOULD automatically select for playback by default in such a situation. A player MAY provide additional settings with more detailed controls for more nuanced scenarios. These examples are provided as guidelines to illustrate the intended usages of the various supported Track flags, and their expected behaviors.

Track names are shown in English for illustrative purposes; actual files may have titles in the language of each track, or provide titles in multiple languages.

21.1. Audio Selection

Example track set:

Table 42: Audio Tracks for default selection
No. Type Lang Layout Original Default Other flags Name
1 Video und N/A N/A N/A None
2 Audio eng 5.1 1 1 None
3 Audio eng 2.0 1 1 None
4 Audio eng 2.0 1 0 Visual-impaired Descriptive audio
5 Audio esp 5.1 0 1 None
6 Audio esp 2.0 0 0 Visual-impaired Descriptive audio
7 Audio eng 2.0 1 0 Commentary Director's Commentary
8 Audio eng 2.0 1 0 None Karaoke

Here we have a file with 7 audio tracks, of which 5 are in English and 2 are in Spanish.

The English tracks all have the Original flag, indicating that English is the original content language.

Generally the player will first consider the track languages: if the player has an option to prefer original-language audio and the user has enabled it, then it should prefer one of the Original-flagged tracks. If configured to specifically prefer audio tracks in English or Spanish, the player should select one of the tracks in the corresponding language. The player may also wish to prefer an Original-flagged track if no tracks matching any of the user's explicitly-preferred languages are available.

Two of the tracks have the Visual-impaired flag. If the player has been configured to prefer such tracks, it should select one; otherwise, it should avoid them if possible.

If selecting an English track, when other settings have left multiple possible options, it may be useful to exclude the tracks that lack the Default flag: here, one provides descriptive service for the visually impaired (which has its own flag and may be automatically selected by user configuration, but is unsuitable for users with default-configured players), one is a commentary track (which has its own flag, which the player may or may not have specialized handling for), and the last contains karaoke versions of the music that plays during the film, which is an unusual specialized audio service that Matroska has no built-in support for indicating, so it's indicated in the track name instead. By not setting the Default flag on these specialized tracks, the file's author hints that they should not be automatically selected by a default-configured player.

Having narrowed its choices down, our example player now may have to select between tracks 2 and 3. The only difference between these tracks is their channel layouts: 2 is 5.1 surround, while 3 is stereo. If the player is aware that the output device is a pair of headphones or stereo speakers, it may wish to prefer the stereo mix automatically. On the other hand, if it knows that the device is a surround system, it may wish to prefer the surround mix.

If the player finishes analyzing all of the available audio tracks and finds that multiple seem equally and maximally preferable, it SHOULD default to the first of the group.

21.2. Subtitle selection

Example track set:

Table 43: Subtitle Tracks for default selection
No. Type Lang Original Default Forced Other flags Name
1 Video und N/A N/A N/A None
2 Audio fra 1 1 N/A None
3 Audio por 0 1 N/A None
4 Subtitles fra 1 1 0 None
5 Subtitles fra 1 0 0 Hearing-impaired Captions for the hearing-impaired
6 Subtitles por 0 1 0 None
7 Subtitles por 0 0 1 None Signs
8 Subtitles por 0 0 0 Hearing-impaired SDH

Here we have 2 audio tracks and 5 subtitle tracks. As we can see, French is the original language.

We'll start by discussing the case where the user prefers French (or Original-language) audio (or has explicitly selected the French audio track), and also prefers French subtitles.

In this case, if the player isn't configured to display captions when the audio matches their preferred subtitle languages, the player doesn't need to select a subtitle track at all.

If the user has indicated that they want captions to be displayed, the selection simply comes down to whether Hearing-impaired subtitles are preferred.

The situation for a user who prefers Portuguese subtitles starts out somewhat analogous. If they select the original French audio (either by explicit audio language preference, preference for Original-language tracks, or by explicitly selecting that track), then the selection once again comes down to the hearing-impaired preference.

However, the case where the Portuguese audio track is selected has an important catch: a Forced track in Portuguese is present. This may contain translations of onscreen text from the video track, or of portions of the audio that are not translated (music, for instance). This means that even if the user's preferences wouldn't normally call for captions here, the Forced track should be selected nonetheless, rather than selecting no track at all. On the other hand, if the user's preferences do call for captions, the non-Forced tracks should be preferred, as the Forced track will not contain captioning for the dialogue.

22. Chapters

The Matroska Chapters system can have multiple Editions and each Edition can consist of Simple Chapters where a chapter start time is used as marker in the timeline only. An Edition can be more complex with Ordered Chapters where a chapter end time stamp is additionally used or much more complex with Linked Chapters. The Matroska Chapters system can also have a menu structure, borrowed from the DVD menu system, or have it's own Native Matroska menu structure.

22.1. EditionEntry

The EditionEntry is also called an Edition. An Edition contains a set of Edition flags and MUST contain at least one ChapterAtom Element. Chapters are always inside an Edition (or a Chapter itself part of an Edition). Multiple Editions are allowed. Some of these Editions MAY be ordered and others not.

22.1.1. EditionFlagDefault

Only one Edition SHOULD have an EditionFlagDefault flag set to true.

22.1.2. Default Edition

The Default Edition is the Edition that a Matroska Player SHOULD use for playback by default.

The first Edition with the EditionFlagDefault flag set to true is the Default Edition.

When all EditionFlagDefault flags are set to false, then the first Edition is the Default Edition.

Table 44: Default edition, all default
Edition FlagDefault Default Edition
Edition 1 true X
Edition 2 true
Edition 3 true
Table 45: Default edition, no default
Edition FlagDefault Default Edition
Edition 1 false X
Edition 2 false
Edition 3 false
Table 46: Default edition, with default
Edition FlagDefault Default Edition
Edition 1 false
Edition 2 true X
Edition 3 false

22.1.3. EditionFlagOrdered

The EditionFlagOrdered Flag is a significant feature as it enables an Edition of Ordered Chapters which defines and arranges a virtual timeline rather than simply labeling points within the timeline. For example, with Editions of Ordered Chapters a single Matroska file can present multiple edits of a film without duplicating content. Alternatively, if a videotape is digitized in full, one Ordered Edition could present the full content (including colorbars, countdown, slate, a feature presentation, and black frames), while another Edition of Ordered Chapters can use Chapters that only mark the intended presentation with the colorbars and other ancillary visual information excluded. If an Edition of Ordered Chapters is enabled, then the Matroska Player MUST play those Chapters in their stored order from the timestamp marked in the ChapterTimeStart Element to the timestamp marked in to ChapterTimeEnd Element.

If the EditionFlagOrdered Flag is set to false, Simple Chapters are used and only the ChapterTimeStart of a Chapter is used as chapter mark to jump to the predefined point in the timeline. With Simple Chapters, a Matroska Player MUST ignore certain Chapter Elements. All these elements are now informational only.

The following list shows the different Chapter elements only found in Ordered Chapters.

Table 47: elements only found in ordered chapters
Ordered Chapter elements
ChapterAtom/ChapterSegmentUID
ChapterAtom/ChapterSegmentEditionUID
ChapterAtom/ChapterTrack
ChapterAtom/ChapProcess
Info/SegmentFamily
Info/ChapterTranslate
TrackEntry/TrackTranslate

Furthermore there are other EBML Elements which could be used if the EditionFlagOrdered flag is set to true.

22.1.3.1. Ordered-Edition and Matroska Segment-Linking
  • Hard Linking: Ordered-Chapters supersedes the Hard Linking.
  • Soft Linking: In this complex system Ordered Chapters are REQUIRED and a Chapter CODEC MUST interpret the ChapProcess of all chapters.
  • Medium Linking: Ordered Chapters are used in a normal way and can be combined with the ChapterSegmentUID element which establishes a link to another Segment.

See Section 19 on the Linked Segments for more information about Hard Linking, Soft Linking, and Medium Linking.

22.2. ChapterAtom

The ChapterAtom is also called a Chapter. A Chapter element can be used recursively. Such a child Chapter is called Nested Chapter.

22.2.1. ChapterTimeStart

The timestamp of the start of Chapter with nanosecond accuracy, not scaled by TimestampScale. For Simple Chapters this is the position of the chapter markers in the timeline.

22.2.2. ChapterTimeEnd

The timestamp of the end of Chapter with nanosecond accuracy, not scaled by TimestampScale. The timestamp defined by the ChapterTimeEnd is not part of the Chapter. A Matroska Player calculates the duration of this Chapter using the difference between the ChapterTimeEnd and ChapterTimeStart. The end timestamp MUST be strictly greater than the start timestamp.

Table 48: ChapterTimeEnd usage possibilities
Chapter Start timestamp End timestamp Duration
Chapter 1 0 1000000000 1000000000
Chapter 2 1000000000 5000000000 4000000000
Chapter 3 6000000000 6000000000 Invalid (0)
Chapter 4 9000000000 8000000000 Invalid (-1000000000)

22.2.3. ChapterFlagHidden

Each Chapter ChapterFlagHidden flag works independently from parent chapters. A Nested Chapter with ChapterFlagHidden flag set to false remains visible even if the Parent Chapter ChapterFlagHidden flag is set to true.

Table 49: ChapterFlagHidden nested visibility
Chapter + Nested Chapter ChapterFlagHidden visible
Chapter 1 false yes
Nested Chapter 1.1 false yes
Nested Chapter 1.2 true no
Chapter 2 true no
Nested Chapter 2.1 false yes
Nested Chapter 2.2 true no

22.4. Physical Types

Each level can have different meanings for audio and video. The ORIGINAL_MEDIUM tag can be used to specify a string for ChapterPhysicalEquiv = 60. Here is the list of possible levels for both audio and video:

Table 50: ChapterPhysicalEquiv meaning per track type
Value Audio Video Comment
70 SET / PACKAGE SET / PACKAGE the collection of different media
60 CD / 12" / 10" / 7" / TAPE / MINIDISC / DAT DVD / VHS / LASERDISC the physical medium like a CD or a DVD
50 SIDE SIDE when the original medium (LP/DVD) has different sides
40 - LAYER another physical level on DVDs
30 SESSION SESSION as found on CDs and DVDs
20 TRACK - as found on audio CDs
10 INDEX - the first logical level of the side/medium

22.5. Chapter Examples

22.5.1. Example 1 : basic chaptering

In this example a movie is split in different chapters. It could also just be an audio file (album) on which each track corresponds to a chapter.

  • 00000ms - 05000ms : Intro
  • 05000ms - 25000ms : Before the crime
  • 25000ms - 27500ms : The crime
  • 27500ms - 38000ms : The killer arrested
  • 38000ms - 43000ms : Credits

This would translate in the following matroska form :

<Chapters>
  <EditionEntry>
    <EditionUID>16603393396715046047</EditionUID>
    <ChapterAtom>
      <ChapterUID>1193046</ChapterUID>
      <ChapterTimeStart>0</ChapterTimeStart>
      <ChapterTimeEnd>5000000000</ChapterTimeEnd>
      <ChapterDisplay>
        <ChapString>Intro</ChapString>
      </ChapterDisplay>
    </ChapterAtom>
    <ChapterAtom>
      <ChapterUID>2311527</ChapterUID>
      <ChapterTimeStart>5000000000</ChapterTimeStart>
      <ChapterTimeEnd>25000000000</ChapterTimeEnd>
      <ChapterDisplay>
        <ChapString>Before the crime</ChapString>
      </ChapterDisplay>
      <ChapterDisplay>
        <ChapString>Avant le crime</ChapString>
        <ChapLanguage>fra</ChapLanguage>
      </ChapterDisplay>
    </ChapterAtom>
    <ChapterAtom>
      <ChapterUID>3430008</ChapterUID>
      <ChapterTimeStart>25000000000</ChapterTimeStart>
      <ChapterTimeEnd>27500000000</ChapterTimeEnd>
      <ChapterDisplay>
        <ChapString>The crime</ChapString>
      </ChapterDisplay>
      <ChapterDisplay>
        <ChapString>Le crime</ChapString>
        <ChapLanguage>fra</ChapLanguage>
      </ChapterDisplay>
    </ChapterAtom>
    <ChapterAtom>
      <ChapterUID>4548489</ChapterUID>
      <ChapterTimeStart>27500000000</ChapterTimeStart>
      <ChapterTimeEnd>38000000000</ChapterTimeEnd>
      <ChapterDisplay>
        <ChapString>After the crime</ChapString>
      </ChapterDisplay>
      <ChapterDisplay>
        <ChapString>Après le crime</ChapString>
        <ChapLanguage>fra</ChapLanguage>
      </ChapterDisplay>
    </ChapterAtom>
    <ChapterAtom>
      <ChapterUID>5666960</ChapterUID>
      <ChapterTimeStart>38000000000</ChapterTimeStart>
      <ChapterTimeEnd>43000000000</ChapterTimeEnd>
      <ChapterDisplay>
        <ChapString>Credits</ChapString>
      </ChapterDisplay>
      <ChapterDisplay>
        <ChapString>Générique</ChapString>
        <ChapLanguage>fra</ChapLanguage>
      </ChapterDisplay>
    </ChapterAtom>
  </EditionEntry>
</Chapters>
Figure 12: Basic Chapters Example.

22.5.2. Example 2 : nested chapters

In this example an (existing) album is split into different chapters, and one of them contain another splitting.

22.5.2.1. The Micronauts "Bleep To Bleep"

  • 00:00 - 12:28 : Baby Wants To Bleep/Rock

    • 00:00 - 04:38 : Baby wants to bleep (pt.1)
    • 04:38 - 07:12 : Baby wants to rock
    • 07:12 - 10:33 : Baby wants to bleep (pt.2)
    • 10:33 - 12:28 : Baby wants to bleep (pt.3)
  • 12:30 - 19:38 : Bleeper_O+2
  • 19:40 - 22:20 : Baby wants to bleep (pt.4)
  • 22:22 - 25:18 : Bleep to bleep
  • 25:20 - 33:35 : Baby wants to bleep (k)
  • 33:37 - 44:28 : Bleeper 
<Chapters>
  <EditionEntry>
    <EditionUID>1281690858003401414</EditionUID>
    <ChapterAtom>
      <ChapterUID>1</ChapterUID>
      <ChapterTimeStart>0</ChapterTimeStart>
      <ChapterTimeEnd>748000000</ChapterTimeEnd>
      <ChapterDisplay>
        <ChapString>Baby wants to Bleep/Rock</ChapString>
      </ChapterDisplay>
      <ChapterAtom>
        <ChapterUID>2</ChapterUID>
        <ChapterTimeStart>0</ChapterTimeStart>
        <ChapterTimeEnd>278000000</ChapterTimeEnd>
        <ChapterDisplay>
          <ChapString>Baby wants to bleep (pt.1)</ChapString>
        </ChapterDisplay>
      </ChapterAtom>
      <ChapterAtom>
        <ChapterUID>3</ChapterUID>
        <ChapterTimeStart>278000000</ChapterTimeStart>
        <ChapterTimeEnd>432000000</ChapterTimeEnd>
        <ChapterDisplay>
          <ChapString>Baby wants to rock</ChapString>
        </ChapterDisplay>
      </ChapterAtom>
      <ChapterAtom>
        <ChapterUID>4</ChapterUID>
        <ChapterTimeStart>432000000</ChapterTimeStart>
        <ChapterTimeEnd>633000000</ChapterTimeEnd>
        <ChapterDisplay>
          <ChapString>Baby wants to bleep (pt.2)</ChapString>
        </ChapterDisplay>
      </ChapterAtom>
      <ChapterAtom>
        <ChapterUID>5</ChapterUID>
        <ChapterTimeStart>633000000</ChapterTimeStart>
        <ChapterTimeEnd>748000000</ChapterTimeEnd>
        <ChapterDisplay>
          <ChapString>Baby wants to bleep (pt.3)</ChapString>
        </ChapterDisplay>
      </ChapterAtom>
    </ChapterAtom>
    <ChapterAtom>
      <ChapterUID>6</ChapterUID>
      <ChapterTimeStart>750000000</ChapterTimeStart>
      <ChapterTimeEnd>1178500000</ChapterTimeEnd>
      <ChapterDisplay>
        <ChapString>Bleeper_O+2</ChapString>
      </ChapterDisplay>
    </ChapterAtom>
    <ChapterAtom>
      <ChapterUID>7</ChapterUID>
      <ChapterTimeStart>1180500000</ChapterTimeStart>
      <ChapterTimeEnd>1340000000</ChapterTimeEnd>
      <ChapterDisplay>
        <ChapString>Baby wants to bleep (pt.4)</ChapString>
      </ChapterDisplay>
    </ChapterAtom>
    <ChapterAtom>
      <ChapterUID>8</ChapterUID>
      <ChapterTimeStart>1342000000</ChapterTimeStart>
      <ChapterTimeEnd>1518000000</ChapterTimeEnd>
      <ChapterDisplay>
        <ChapString>Bleep to bleep</ChapString>
      </ChapterDisplay>
    </ChapterAtom>
    <ChapterAtom>
      <ChapterUID>9</ChapterUID>
      <ChapterTimeStart>1520000000</ChapterTimeStart>
      <ChapterTimeEnd>2015000000</ChapterTimeEnd>
      <ChapterDisplay>
        <ChapString>Baby wants to bleep (k)</ChapString>
      </ChapterDisplay>
    </ChapterAtom>
    <ChapterAtom>
      <ChapterUID>10</ChapterUID>
      <ChapterTimeStart>2017000000</ChapterTimeStart>
      <ChapterTimeEnd>2668000000</ChapterTimeEnd>
      <ChapterDisplay>
        <ChapString>Bleeper</ChapString>
      </ChapterDisplay>
    </ChapterAtom>
  </EditionEntry>
</Chapters>
Figure 13: Nested Chapters Example.

23. Attachments

Matroska supports storage of related files and data in the Attachments Element (a Top-Level Element). Attachment Elements can be used to store related cover art, font files, transcripts, reports, error recovery files, picture, or text-based annotations, copies of specifications, or other ancillary files related to the Segment.

Matroska Readers MUST NOT execute files stored as Attachment Elements.

23.1. Cover Art

This section defines a set of guidelines for the storage of cover art in Matroska files. A Matroska Reader MAY use embedded cover art to display a representational still-image depiction of the multimedia contents of the Matroska file.

Only JPEG and PNG image formats SHOULD be used for cover art pictures.

There can be two different covers for a movie/album: a portrait style (e.g., a DVD case) and a landscape style (e.g., a wide banner ad).

There can be two versions of the same cover, the normal cover and the small cover. The dimension of the normal cover SHOULD be 600 pixels on the smallest side -- for example, 960x600 for landscape, 600x800 for portrait, or 600x600 for square. The dimension of the small cover SHOULD be 120 pixels on the smallest side -- for example, 192x120 or 120x160.

Versions of cover art can be differentiated by the filename, which is stored in the FileName Element. The default filename of the normal cover in square or portrait mode is cover.(jpg|png). When stored, the normal cover SHOULD be the first Attachment in storage order. The small cover SHOULD be prefixed with "small_", such as small_cover.(jpg|png). The landscape variant SHOULD be suffixed with "_land", such as cover_land.(jpg|png). The filenames are case sensitive.

The following table provides examples of file names for cover art in Attachments.

Table 51: Cover Art Filenames
FileName Image Orientation Pixel Length of Smallest Side
cover.jpg Portrait or square 600
small_cover.png Portrait or square 120
cover_land.png Landscape 600
smallcoverland.jpg Landscape 120

24. Cues

The Cues Element provides an index of certain Cluster Elements to allow for optimized seeking to absolute timestamps within the Segment. The Cues Element contains one or many CuePoint Elements which each MUST reference an absolute timestamp (via the CueTime Element), a Track (via the CueTrack Element), and a Segment Position (via the CueClusterPosition Element). Additional non-mandated Elements are part of the CuePoint Element such as CueDuration, CueRelativePosition, CueCodecState and others which provide any Matroska Reader with additional information to use in the optimization of seeking performance.

24.1. Recommendations

The following recommendations are provided to optimize Matroska performance.

  • Unless Matroska is used as a live stream, it SHOULD contain a Cues Element.
  • For each video track, each keyframe SHOULD be referenced by a CuePoint Element.
  • It is RECOMMENDED to not reference non-keyframes of video tracks in Cues unless it references a Cluster Element which contains a CodecState Element but no keyframes.
  • For each subtitle track present, each subtitle frame SHOULD be referenced by a CuePoint Element with a CueDuration Element.
  • References to audio tracks MAY be skipped in CuePoint Elements if a video track is present. When included the CuePoint Elements SHOULD reference audio keyframes at most once every 500 milliseconds.
  • If the referenced frame is not stored within the first SimpleBlock, or first BlockGroup within its Cluster Element, then the CueRelativePosition Element SHOULD be written to reference where in the Cluster the reference frame is stored.
  • If a CuePoint Element references Cluster Element that includes a CodecState Element, then that CuePoint Element MUST use a CueCodecState Element.
  • CuePoint Elements SHOULD be numerically sorted in storage order by the value of the CueTime Element.

25. Matroska Streaming

In Matroska, there are two kinds of streaming: file access and livestreaming.

25.1. File Access

File access can simply be reading a file located on your computer, but also includes accessing a file from an HTTP (web) server or CIFS (Windows share) server. These protocols are usually safe from reading errors and seeking in the stream is possible. However, when a file is stored far away or on a slow server, seeking can be an expensive operation and SHOULD be avoided. The following guidelines, when followed, help reduce the number of seeking operations for regular playback and also have the playback start quickly without a lot of data needed to read first (like a Cues Element, Attachment Element or SeekHead Element).

Matroska, having a small overhead, is well suited for storing music/videos on file servers without a big impact on the bandwidth used. Matroska does not require the index to be loaded before playing, which allows playback to start very quickly. The index can be loaded only when seeking is requested the first time.

25.2. Livestreaming

Livestreaming is the equivalent of television broadcasting on the internet. There are 2 families of servers for livestreaming: RTP/RTSP and HTTP. Matroska is not meant to be used over RTP. RTP already has timing and channel mechanisms that would be wasted if doubled in Matroska. Additionally, having the same information at the RTP and Matroska level would be a source of confusion if they do not match. Livestreaming of Matroska over HTTP (or any other plain protocol based on TCP) is possible.

A live Matroska stream is different from a file because it usually has no known end (only ending when the client disconnects). For this, all bits of the "size" portion of the Segment Element MUST be set to 1. Another option is to concatenate Segment Elements with known sizes, one after the other. This solution allows a change of codec/resolution between each segment. For example, this allows for a switch between 4:3 and 16:9 in a television program.

When Segment Elements are continuous, certain Elements, like MetaSeek, Cues, Chapters, and Attachments, MUST NOT be used.

It is possible for a Matroska Player to detect that a stream is not seekable. If the stream has neither a MetaSeek list or a Cues list at the beginning of the stream, it SHOULD be considered non-seekable. Even though it is possible to seek blindly forward in the stream, it is NOT RECOMMENDED.

In the context of live radio or web TV, it is possible to "tag" the content while it is playing. The Tags Element can be placed between Clusters each time it is necessary. In that case, the new Tags Element MUST reset the previously encountered Tags Elements and use the new values instead.

26. IANA Considerations

26.3. Historic Deprecated Element IDs Registry

As Matroska evolved since 2002 many parts that were considered for use in the format were never used and often incorrectly designed. Many of the elements that were then defined are not found in any known files but were part of public specs. DivX also had a few custom elements that were designed for custom features.

We list these elements that have a known ID that SHOULD NOT be reused to avoid colliding with existing files.

26.3.1. SilentTracks Element

path:
\Segment\Cluster\SilentTracks
id:
0x5854
type:
master
definition:
The list of tracks that are not used in that part of the stream. It is useful when using overlay tracks on seeking or to decide what track to use.

26.3.2. SilentTrackNumber Element

path:
\Segment\Cluster\SilentTracks\SilentTrackNumber
id:
0x58D7
type:
uinteger
definition:
One of the track number that are not used from now on in the stream. It could change later if not specified as silent in a further Cluster.

26.3.3. BlockVirtual Element

path:
\Segment\Cluster\BlockGroup\BlockVirtual
id:
0xA2
type:
binary
definition:
A Block with no data. It MUST be stored in the stream at the place the real Block would be in display order.

26.3.4. ReferenceVirtual Element

path:
\Segment\Cluster\BlockGroup\ReferenceVirtual
id:
0xFD
type:
integer
definition:
The Segment Position of the data that would otherwise be in position of the virtual block.

26.3.5. FrameNumber Element

path:
\Segment\Cluster\BlockGroup\Slices\TimeSlice\FrameNumber
id:
0xCD
type:
uinteger
definition:
The number of the frame to generate from this lace with this delay (allow you to generate many frames from the same Block/Frame).

26.3.6. BlockAdditionID Element

path:
\Segment\Cluster\BlockGroup\Slices\TimeSlice\BlockAdditionID
id:
0xCB
type:
uinteger
definition:
The ID of the BlockAdditional Element (0 is the main Block).

26.3.7. Delay Element

path:
\Segment\Cluster\BlockGroup\Slices\TimeSlice\Delay
id:
0xCE
type:
uinteger
definition:
The (scaled) delay to apply to the Element.

26.3.8. SliceDuration Element

path:
\Segment\Cluster\BlockGroup\Slices\TimeSlice\SliceDuration
id:
0xCF
type:
uinteger
definition:
The (scaled) duration to apply to the Element.

26.3.9. ReferenceFrame Element

path:
\Segment\Cluster\BlockGroup\ReferenceFrame
id:
0xC8
type:
master
definition:
Contains information about the last reference frame. See [DivXTrickTrack].

26.3.10. ReferenceOffset Element

path:
\Segment\Cluster\BlockGroup\ReferenceFrame\ReferenceOffset
id:
0xC9
type:
uinteger
definition:
The relative offset, in bytes, from the previous BlockGroup element for this Smooth FF/RW video track to the containing BlockGroup element. See [DivXTrickTrack].

26.3.11. ReferenceTimestamp Element

path:
\Segment\Cluster\BlockGroup\ReferenceFrame\ReferenceTimestamp
id:
0xCA
type:
uinteger
definition:
The timecode of the BlockGroup pointed to by ReferenceOffset. See [DivXTrickTrack].

26.3.12. EncryptedBlock Element

path:
\Segment\Cluster\EncryptedBlock
id:
0xAF
type:
binary
definition:
Similar to SimpleBlock, see Section 12.4, but the data inside the Block are Transformed (encrypt and/or signed).

26.3.13. TrackOffset Element

path:
\Segment\Tracks\TrackEntry\TrackOffset
id:
0x537F
type:
integer
definition:
A value to add to the Block's Timestamp. This can be used to adjust the playback offset of a track.

26.3.14. CodecSettings Element

path:
\Segment\Tracks\TrackEntry\CodecSettings
id:
0x3A9697
type:
utf-8
definition:
A string describing the encoding setting used.

26.3.15. CodecInfoURL Element

path:
\Segment\Tracks\TrackEntry\CodecInfoURL
id:
0x3B4040
type:
string
definition:
A URL to find information about the codec used.

26.3.16. CodecDownloadURL Element

path:
\Segment\Tracks\TrackEntry\CodecDownloadURL
id:
0x26B240
type:
string
definition:
A URL to download about the codec used.

26.3.17. CodecDecodeAll Element

path:
\Segment\Tracks\TrackEntry\CodecDecodeAll
id:
0xAA
type:
uinteger
definition:
Set to 1 if the codec can decode potentially damaged data.

26.3.18. OldStereoMode Element

path:
\Segment\Tracks\TrackEntry\Video\OldStereoMode
id:
0x53B9
type:
uinteger
definition:
DEPRECATED, DO NOT USE. Bogus StereoMode value used in old versions of libmatroska.

26.3.19. AspectRatioType Element

path:
\Segment\Tracks\TrackEntry\Video\AspectRatioType
id:
0x54B3
type:
uinteger
definition:
Specify the possible modifications to the aspect ratio.

26.3.20. GammaValue Element

path:
\Segment\Tracks\TrackEntry\Video\GammaValue
id:
0x2FB523
type:
float
definition:
Gamma Value.

26.3.21. FrameRate Element

path:
\Segment\Tracks\TrackEntry\Video\FrameRate
id:
0x2383E3
type:
float
definition:
Number of frames per second. This value is Informational only. It is intended for constant frame rate streams, and SHOULD NOT be used for a variable frame rate TrackEntry.

26.3.22. ChannelPositions Element

path:
\Segment\Tracks\TrackEntry\Audio\ChannelPositions
id:
0x7D7B
type:
binary
definition:
Table of horizontal angles for each successive channel.

26.3.23. TrickTrackUID Element

path:
\Segment\Tracks\TrackEntry\TrickTrackUID
id:
0xC0
type:
uinteger
definition:
The TrackUID of the Smooth FF/RW video in the paired EBML structure corresponding to this video track. See [DivXTrickTrack].

26.3.24. TrickTrackSegmentUID Element

path:
\Segment\Tracks\TrackEntry\TrickTrackSegmentUID
id:
0xC1
type:
binary
definition:
The SegmentUID of the Segment containing the track identified by TrickTrackUID. See [DivXTrickTrack].

26.3.25. TrickTrackFlag Element

path:
\Segment\Tracks\TrackEntry\TrickTrackFlag
id:
0xC6
type:
uinteger
definition:
Set to 1 if this video track is a Smooth FF/RW track. If set to 1, MasterTrackUID and MasterTrackSegUID should must be present and BlockGroups for this track must contain ReferenceFrame structures. Otherwise, TrickTrackUID and TrickTrackSegUID must be present if this track has a corresponding Smooth FF/RW track. See [DivXTrickTrack].

26.3.26. TrickMasterTrackUID Element

path:
\Segment\Tracks\TrackEntry\TrickMasterTrackUID
id:
0xC7
type:
uinteger
definition:
The TrackUID of the video track in the paired EBML structure that corresponds to this Smooth FF/RW track. See [DivXTrickTrack].

26.3.27. TrickMasterTrackSegmentUID Element

path:
\Segment\Tracks\TrackEntry\TrickMasterTrackSegmentUID
id:
0xC4
type:
binary
definition:
The SegmentUID of the Segment containing the track identified by MasterTrackUID. See [DivXTrickTrack].

26.3.28. ContentSignature Element

path:
\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentEncryption\ContentSignature
id:
0x47E3
type:
binary
definition:
A cryptographic signature of the contents.

26.3.29. ContentSigKeyID Element

path:
\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentEncryption\ContentSigKeyID
id:
0x47E4
type:
binary
definition:
This is the ID of the private key the data was signed with.

26.3.30. ContentSigAlgo Element

path:
\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentEncryption\ContentSigAlgo
id:
0x47E5
type:
uinteger
definition:
The algorithm used for the signature.

26.3.31. ContentSigHashAlgo Element

path:
\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentEncryption\ContentSigHashAlgo
id:
0x47E6
type:
uinteger
definition:
The hash algorithm used for the signature.

26.3.32. CueRefCluster Element

path:
\Segment\Cues\CuePoint\CueTrackPositions\CueReference\CueRefCluster
id:
0x97
type:
uinteger
definition:
The Segment Position of the Cluster containing the referenced Block.

26.3.33. CueRefNumber Element

path:
\Segment\Cues\CuePoint\CueTrackPositions\CueReference\CueRefNumber
id:
0x535F
type:
uinteger
definition:
Number of the referenced Block of Track X in the specified Cluster.

26.3.34. CueRefCodecState Element

path:
\Segment\Cues\CuePoint\CueTrackPositions\CueReference\CueRefCodecState
id:
0xEB
type:
uinteger
definition:
The Segment Position of the Codec State corresponding to this referenced Element. 0 means that the data is taken from the initial Track Entry.

26.3.35. FileReferral Element

path:
\Segment\Attachments\AttachedFile\FileReferral
id:
0x4675
type:
binary
definition:
A binary value that a track/codec can refer to when the attachment is needed.

26.3.36. FileUsedStartTime Element

path:
\Segment\Attachments\AttachedFile\FileUsedStartTime
id:
0x4661
type:
uinteger
definition:
The timecode at which this optimized font attachment comes into context, based on the Segment TimecodeScale. This element is reserved for future use and if written must be the segment start time. See [DivXWorldFonts].

26.3.37. FileUsedEndTime Element

path:
\Segment\Attachments\AttachedFile\FileUsedEndTime
id:
0x4662
type:
uinteger
definition:
The timecode at which this optimized font attachment goes out of context, based on the Segment TimecodeScale. This element is reserved for future use and if written must be the segment end time. See [DivXWorldFonts].

26.3.38. TagDefaultBogus Element

path:
\Segment\Tags\Tag\+SimpleTag\TagDefaultBogus
id:
0x44B4
type:
uinteger
definition:
A variant of the TagDefault element with a bogus Element ID; see Section 8.1.8.1.2.4.

27. Normative References

[BCP47]
Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying Languages", , DOI 10.17487/RFC5646, , <https://www.rfc-editor.org/info/rfc5646>.
[Blowfish]
Schneier, B., "The Blowfish Encryption Algorithm", , , <https://www.schneier.com/academic/blowfish/>.
[BZIP2]
Seward, J., "bzip2", , , <https://sourceware.org/bzip2/>.
[FIPS.197]
US National Institute of Standards and Technology, "Advanced Encryption Standard (AES)", , DOI 10.6028/NIST.FIPS.197, , <https://csrc.nist.gov/publications/detail/fips/197/final>.
[FIPS.46-3]
US National Institute of Standards and Technology, "Data Encryption Standard (DES)", , FIPS PUB 46, , <https://csrc.nist.gov/publications/detail/fips/46/3/archive/1999-10-25>.
[IANADomains]
"IANA Root Zone Database", , <https://www.iana.org/domains/root/db>.
[IANALangRegistry]
"IANA Language Subtag Registry", , , <https://www.iana.org/assignments/language-subtag-registry/language-subtag-registry>.
[ISO3166-1]
International Organization for Standardization, "Codes for the representation of names of countries and their subdivisions -- Part 1: Country code", , ISO 3166-1:2020, , <https://www.iso.org/standard/72482.html>.
[ISO639-2]
United States Library Of Congress, "Codes for the Representation of Names of Languages", , ISO 639-2:1998, , <https://www.loc.gov/standards/iso639-2/php/code_list.php>.
[LZO]
Tarreau, W., Rodgman, R., and M. Oberhumer, "Lempel–Ziv–Oberhumer compression", , , <https://www.kernel.org/doc/Documentation/lzo.txt>.
[MatroskaCodec]
Lhomme, S., Bunkus, M., and D. Rice, "Media Container Codec Specifications", , Work in Progress, Internet-Draft, draft-ietf-cellar-codec-06, , <https://datatracker.ietf.org/doc/html/draft-ietf-cellar-codec-06>.
[MatroskaTags]
Lhomme, S., Bunkus, M., and D. Rice, "Matroska Media Container Tag Specifications", , Work in Progress, Internet-Draft, draft-ietf-cellar-tags-06, , <https://datatracker.ietf.org/doc/html/draft-ietf-cellar-tags-06>.
[RFC1851]
Karn, P., Metzger, P., and W. Simpson, "The ESP Triple DES Transform", RFC 1851, DOI 10.17487/RFC1851, , <https://www.rfc-editor.org/info/rfc1851>.
[RFC1950]
Deutsch, P. and J-L. Gailly, "ZLIB Compressed Data Format Specification version 3.3", RFC 1950, DOI 10.17487/RFC1950, , <https://www.rfc-editor.org/info/rfc1950>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/info/rfc8174>.
[RFC8794]
Lhomme, S., Rice, D., and M. Bunkus, "Extensible Binary Meta Language", RFC 8794, DOI 10.17487/RFC8794, , <https://www.rfc-editor.org/info/rfc8794>.
[Twofish]
Schneier, B., Kelsey, J., Whiting, D., Wagner, D., Hall, C., and N. Ferguson, "Twofish: A 128-Bit Block Cipher", , , <https://www.schneier.com/academic/twofish/>.
[WebVTT]
Pieters, S., Pfeiffer, S., Ed., Jägenstedt, P., and I. Hickson, "WebVTT Cue Identifier", , , <https://www.w3.org/TR/webvtt1/#webvtt-cue-identifier>.

28. Informative References

[DivXTrickTrack]
"DivX Trick Track Extensions", , , <http://web.archive.org/web/20101222001148/http://labs.divx.com/node/16601>.
[DivXWorldFonts]
"DivX World Fonts Extensions", , , <http://web.archive.org/web/20110214132246/http://labs.divx.com/node/16602>.
[MCF]
"Media Container Format", , , <http://mukoli.free.fr/mcf/mcf.html>.

Authors' Addresses

Steve Lhomme
Moritz Bunkus
Dave Rice