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Matroska Chapter Codecs

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.

Segment Linking

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:

  • ChapterTranslate\ChapterTranslateCodec = 1

  • ChapterTranslate\ChapterTranslateID = "SegB"

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.

Matroska Chapter Codecs and Nested Chapters

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.

Matroska Script

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.

DVD Menu

This is the case when ChapProcessCodecID = 1. Each level of a chapter corresponds to a logical level in the DVD system [@?DVD-Video] that is stored in the first octet of the ChapProcessPrivate. This DVD hierarchy is as follows:

ChapProcessPrivate DVD Name Hierarchy Commands Possible Comment
0x30 SS DVD domain - First Play, Video Manager, Video Title
0x2A LU Language Unit - Contains only PGCs
0x28 TT Title - Contains only PGCs
0x20 PGC Program Group Chain (PGC) *
0x18 PG Program 1 / Program 2 / Program 3 -
0x10 PTT Part Of Title 1 / Part Of Title 2 - Equivalent to the chapters on the sleeve.
0x08 CN Cell 1 / Cell 2 / Cell 3 / Cell 4 / Cell 5 / Cell 6 -

You can also recover wether a Segment is a Video Manager (VMG), Video Title Set (VTS) or Video Title Set Menu (VTSM) from the ChapterTranslateID element found in the Segment Info. This field uses 2 octets as follows:

  1. Domain Type: 0 for VMG, the domain number for VTS and VTSM

  2. Domain Value: 0 for VMG and VTSM, 1 for the VTS source.

For instance, the menu part from VTS_01_0.VOB would be coded [1,0] and the content part from VTS_02_3.VOB would be [2,1]. The VMG is always [0,0]

The following octets of ChapProcessPrivate are as follows:

Octet 1 DVD Name Following Octets
0x30 SS Domain name code (1: 0x00= First play, 0xC0= VMG, 0x40= VTSM, 0x80= VTS) + VTS(M) number (2)
0x2A LU Language code (2) + Language extension (1)
0x28 TT global Title number (2) + corresponding TTN of the VTS (1)
0x20 PGC PGC number (2) + Playback Type (1) + Disabled User Operations (4)
0x18 PG Program number (2)
0x10 PTT PTT-chapter number (1)
0x08 CN Cell number [VOB ID(2)][Cell ID(1)][Angle Num(1)]

If the level specified in ChapProcessPrivate is a PGC (0x20), there is an octet called the Playback Type, specifying the kind of PGC defined:

  • 0x00: entry only/basic PGC

  • 0x82: Title+Entry Menu (only found in the Video Manager domain)

  • 0x83: Root Menu (only found in the VTSM domain)

  • 0x84: Subpicture Menu (only found in the VTSM domain)

  • 0x85: Audio Menu (only found in the VTSM domain)

  • 0x86: Angle Menu (only found in the VTSM domain)

  • 0x87: Chapter Menu (only found in the VTSM domain)

The next 4 following octets correspond to the User Operation flags in the standard PGC. When a bit is set, the command SHOULD be disabled.

ChapProcessData contains the pre/post/cell commands in binary format as there are stored on a DVD. There is just an octet preceding these data to specify the number of commands in the element. As follows: [# of commands(1)][command 1 (8)][command 2 (8)][command 3 (8)].

More information on the DVD commands and format on DVD from the [@?DVD-Info] project and [@?Inside-DVD-Video].