Matroska is a multimedia container format based on EBML that can contain multiple audio, video, and subtitle streams. It defines elements like Segment, SeekHead, Info, Tracks, Cluster, Cues, Attachments and Tags that provide structure and metadata for playback. Codec Mappings are used to identify and describe the encoding of data within each track. A sample Matroska file is analyzed to demonstrate these elements.

1. What is Matroska?
Hossein Yavari
May 2023

2. Intro
- Matroska is an audiovisual data container format.
- It is based on EBML (Extensible Binary Meta Language).
- EBML: a binary derivative of XML
- It is a only a container; that means:
- It is NOT a video or audio compression format (codec),
- It is an envelope in which there can be many audio, video, and subtitles streams.

3. Common terms
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.
Matroska Writer:
• A data writer that creates Matroska documents.

4. Data Layout
• A Matroska file must be composed of at least
one EBML document.
• Each EBML document starts with an EBML
Header and must be followed by the EBML Root
Element.
• EBML root element, defined as Segment in
Matroska.
• Matroska defines several Top-Level Elements
which may occur within the Segment.

5. Data Layout (Cont.)
The Matroska EBML schema defines eight Top-Level Elements:
• SeekHead ((#seekhead)),
• Info ((#info)),
• Tracks ((#track-flags)),
• Chapters ((#chapters)),
• Cluster ((#block-structure)),
• Cues ((#cues)),
• Attachments ((#attachments-1)),
• Tags ((#tags)).

6. Data Layout (Cont.)
• SeekHead Element (also known as MetaSeek)
contains an index of Top-Level Elements locations
within the Segment.
• Without a SeekHead Element, a Matroska parser
would have to search the entire file to find all the
other Top-Level Elements.
❑ Value details:
https://www.matroska.org/technical/elements.html#:~:text=Meta%20Seek%
20Information

7. Data Layout (Cont.)
• The Info Element contains vital information for
identifying the whole Segment; includes the
title for the Segment, a randomly generated
unique identifier.
❑ Value details:
https://www.matroska.org/technical/elements.html#:~:text=Descripti
on-,Segment%20Information,-Info

8. Data Layout (Cont.)
• 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.

9. Data Layout (Cont.)
• The Tracks Element MUST identify all the data
needed by the codec to decode the data of the
specified track.
• 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.
❑ Value details:
https://www.matroska.org/technical/elements.html#:~:text=Descripti
on-,Track,-Tracks

10. Data Layout (Cont.)
• The Chapters Element lists all the chapters.
• Chapters are a way to set predefined points
to jump to in video or audio.
❑ Value details:
https://www.matroska.org/technical/elements.html#:~:text=Des
cription-,Chapters,-Chapters

11. Data Layout (Cont.)
• Cluster Elements contain the content for each track, e.g.,
video frames.
• Every Cluster Element MUST contain a Timestamp Element.
• Timestamp Element used to play the first Block in the
Cluster Element.
• The Cluster Element helps to break up SimpleBlock or
BlockGroup Elements and helps with seeking and error
protection.
• A Matroska file should contain at least one Cluster Element.
❑ Value details:
https://www.matroska.org/technical/elements.html#:~:text=Description-
,Cluster,-Cluster

12. Data Layout (Cont.)
• 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.
❑ Value details:
https://www.matroska.org/technical/elements.html#:~:text=Descripti
on-,Cueing%20Data,-Cues

13. Data Layout (Cont.)
• The Attachments Element is for attaching files to
a Matroska file such as pictures, fonts,
webpages, etc.
❑ Value details:
https://www.matroska.org/technical/elements.html#:~:text=Des
cription-,Attachment,-Attachments

14. Data Layout (Cont.)
• 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.
• Tags can contain their values in multiple
languages.
❑ Value details:
https://www.matroska.org/technical/elements.html#:~:text=Des
cription-,Tagging,-Tags

15. Codec Mapping

16. Codec Mapping
• A Codec Mapping is a set of attributes to identify, name, and contextualize the format
and characteristics of encoded data that can be contained within Matroska Clusters.
• Each TrackEntry used within Matroska must reference a defined Codec Mapping using
the Codec ID to identify and describe the format of the encoded data in its associated
Clusters.
• Codec ID is a unique registered identifier that represents the encoding stored within the
Track.

17. Codec Mapping (Cont.)
• Codec ID must be prefixed with the string from the table
according to the associated type of the codec.
• Each Codec ID must include a Major Codec ID
immediately following the Codec ID Prefix.
• A Major Codec ID may be followed by an OPTIONAL
Codec ID Suffix to communicate a refinement of the
Major Codec ID.
• If a Codec ID Suffix is used, then the Codec ID MUST
include a forward slash (“/”) as a separator between the
Major Codec ID and the Codec ID Suffix.

18. Sample File Analysis

19. Sample file
https://mkvtoolnix.
download/downlo
ads.html
MP3 file
converted to
MKV via
ffmpeg.

20. Sample file
EBML header

21. Sample file
Segment

22. Sample file
379-52 = 237
Seekhead

23. Sample file
Segment Info

24. Sample file
Tracks

25. Sample file
Cluster

26. Sample file
Cues

27. Sample file
Tags

28. REFERENCES
- https://www.matroska.org/index.html
- https://mkvtoolnix.download/downloads.html

29. Thank You.
H.Yavari