| Internet-Draft | Matroska Chapter Codecs | August 2024 |
| Lhomme, et al. | Expires 1 March 2025 | [Page] |
This document defines common Matroska Chapter Codecs, the basic Matroska Script and the DVD inspired DVD menu [DVD-Video].¶
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The [Matroska] container can be expanded with Matroska Chapter Codecs. They define a set of instructions
that the Matroska Player should execute when entering, leaving or during playback of a Chapter.
This allows extra features not provided by the classical linear playback of files.¶
The Matroska Chapter Codecs codec is extensible. So any new codec can be created and support added in players.¶
This document is a work-in-progress specification defining the Matroska file format as part of the IETF Cellar working group. It uses basic elements and concept already defined in the Matroska specifications defined by this workgroup [Matroska].¶
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.¶
Chapter codecs are a way to add more complex playback features than the usual linear playback.¶
Some ChapProcess elements hold commands to execute when entering/leaving a chapter.¶
When chapter codecs are used the EditionFlagOrdered of the edition they belong to MUST be set.¶
Each ChapProcessCodecID value in an edition SHOULD have a single interpreter for the whole EditionEntry,
if that ChapProcessCodecID value is supported by the Matroska Player.
This is necessary to be able to read/write global variables that can be used between chapters.¶
Chapter Codecs can reference another Segment and jump to that Segment.¶
The Chapter Codecs MAY store the Segment information in their own format, possibly not using the SegmentUUID format.
The ChapterTranslate element and its child elements SHOULD be used
to link the internal chapter codec representation, the chapter codec number and the actual Segment it represents.¶
For example, if a chapter codec of type "1" in SegmentA needs to link to SegmentB, it can store that information as "SegB" in its internal data.¶
The translation ChapterTranslate in SegmentB would use the following elements:¶
The Matroska Player MUST use the SegmentFamily to find all Segments that need translation
between the chapter codec values and the actual segment it targets.¶
When Nested Chapters contain chapters codecs -- via the ChapProcess element --
the enter/leave commands -- ChapProcessTime element -- MUST be executed in a specific order,
if the Matroska Player supports the chapter codecs included in the chapters.¶
When starting playback, the Matroska Player MUST start at the ChapterTimeStart of the first chapter of the ordered chapter.
The enter commands of that chapter MUST be executed.
If that chapter contains Nested Chapters, the enter commands of the Nested Chapter with the same ChapterTimeStart MUST be executed.
If that chapter contains Nested Chapters, the enter commands of the Nested Chapter with the same ChapterTimeStart MUST be executed,
and so on until there is no Nested Chapter with the same ChapterTimeStart.¶
When switching from a chapter to another:¶
the leave commands (ChapProcessTime=2) of the
chapter MUST be executed, then the leave commands of its parent chapter, etc., until the
common Parent Chapter or Edition element. The leave command of that Parent Chapter or Edition element
MUST NOT be executed.¶
the enter commands (ChapProcessTime=1) of the Nested Chapter of the common Parent Chapter or Edition element,
to reach the chapter we switch to, MUST be executed, then the enter commands of its Nested Chapter
to reach the chapter we switch to MUST be executed, until that chapter is the chapter we switch to.
The enter commands of that chapter MUST be executed as well.¶
When the last Chapter finished playing, i.e., its ChapterTimeEnd has been reached,
the Matroska Player MUST execute its leaved commands, then the leave commands of it's Parent Chapter,
until the parent of the chapter is the Edition.¶
This is the case when ChapProcessCodecID = 0. This is a script language build for
Matroska purposes. The inspiration comes from [ActionScript], [ECMAScript] and other similar
scripting languages. The commands are stored as text commands, in UTF-8. The syntax is C like,
with commands spanned on many lines, each terminating with a semicolon ";". You can also include comments
at the end of lines with "//" or comment many lines using "/* */". The scripts are stored
in ChapProcessData. For the moment ChapProcessPrivate is not used.¶
The one and only command existing for the moment is GotoAndPlay( ChapterUID );. As the
same suggests, it means that, when this command is encountered, the Matroska Player
SHOULD jump to the Chapter specified by the UID and play it, as long as this Chapter exists.¶
Tag values can be either strings or binary blobs. This document inherits security
considerations from the EBML [RFC8794] and Matroska [Matroska] documents.¶
The Chapter Codec ID values set in ChapProcessCodecID use the Matroska Chapter Codec IDs Registry
defined in [Matroska].¶
The initial values 0 and 1 are defined in Section 5.1 and Section 5.2 respectively.¶