Underspecified chapter interactions

[pitdicker]

I'm trying to write a small tool for working with editions and chapters, and there are a number of interactions that I am not sure off how to interpret the spec. I may add more comments to this issue as I encounter them. Maybe they will help to make the spec clearer.

May simple chapters be out of order?

Should the order of ChapterAtoms in an EditionEntry be sorted based on ChapterTimeStart, or may they be out of order?

For example is it allowed to have chapters present with start times in this order:

• Chapter 3: 10:00:00
• Chapter 2: 05:00:00
• Chapter 1: 00:00:00

What happens if simple chapters overlap?

The ChapterTimeEnd of one chapter may be greater than the ChapterTimeStart of the next chapter. Should ChapterTimeEnd be considered informative, that can be overruled by the next ChapterTimeStart?

Consider:

- Chapter names:
    - 00:00:00 - 00:02:00   `ChapString`: "Beginning"
    - 00:02:00 - 00:38:00   `ChapString`: "Core"
    - 00:38:00 - 00:40:00   `ChapString`: "Conclusion"
- Skip info:
    - 00:00:00 - 00:00:20   `ChapterSkipType`: Opening Credits
    - 00:00:20 - 00:39:40   `ChapterSkipType`: No Skipping
    - 00:39:40 - 00:40:00   `ChapterSkipType`: End Credits
- Physical medium:
    - 00:00:00 - 00:30:00   `ChapterPhysicalEquiv`: 50 (tape side 1)
    - 00:30:00 - 00:40:00   `ChapterPhysicalEquiv`: 50 (tape side 2)

As I understand it a structure like this is currently allowed by the spec. Maybe it is better to require nested and hidden chapters to represent such data?

The same data represented with nested chapters:

- 00:00:00 - 00:30:00   `ChapterPhysicalEquiv`: 50 (hidden)
    - 00:00:00 - 00:02:00   `ChapString`: "Beginning" (visible)
        - 00:00:00 - 00:00:20   `ChapterSkipType`: Opening Credits (hidden)
    - 00:02:00 - 00:30:00   `ChapString`: "Core"
- 00:30:00 - 00:40:00   `ChapterPhysicalEquiv`: 50 (tape side 2) (hidden)
    - 00:30:00 - 00:38:00   `ChapString`: "Core" (hidden?)
    - 00:38:00 - 00:40:00   `ChapString`: "Conclusion" (visible)
        - 00:00:00 - 00:00:20   `ChapterSkipType`: End Credits (hidden)

What happens when two chapters overlap that have different names (what name does a player show as the current chapter name)? What happens if they have different ChapterFlagEnabled? Different ChapterSkipTypes?

How do ChapterFlagHidden and ChapterSkipType interact?

A hidden chapter should not be available in the user interface. ChapterSkipType can inform users of the content of a chapter, and allow automatic skipping in the player. Wouldn't it be confusing if a portion of a video was automatically skipped, while no information about it is presented in the user interface?

I would think the presence of ChapterSkipType overrides ChapterFlagHidden to false. Or maybe should ChapterFlagHidden only influence a chapter list/timeline with timestamps and optionally names?

What happens if a simple chapter is disabled?

When disabled, the movie SHOULD skip all the content between the TimeStart and TimeEnd of this chapter.

Does this mean that even for editions that don't use unordered chapters that a virtual timeline should be constructed, where the total duration of the movie is shortened?

The quoted line mentiones TimeEnd. This is implied to be the time until the next ChapterTimeStart if it is not present?

How do nested chapters interact with ChapterFlagEnabled?

What happens if a parent chapter is disabled, but a child chapter is enabled? Does this work the same as with ChapterFlagHidden?

[pitdicker]

I see ChapterSkipType is not yet really part of the spec, and ChapterFlagEnabled is removed from the main text but does have a description of how to work with nested chapters.

[robUx4]

May simple chapters be out of order?

yes

What happens if simple chapters overlap?

It's fine. It allows tagging to content that is actually overlapping. And also identify the overlapping parts.
This is not possible for Ordered Editions.

How do ChapterFlagHidden and ChapterSkipType interact?

They are unreleated. ChapterFlagHidden is mostly for use with chapter codecs to hide/show them but it currently not used.

ChapterSkipType is part of Matroska v5 and not implemented anywhere as far as I know (but I'm planning on adding it to VLC).

What happens if a simple chapter is disabled? Does this mean that even for editions that don't use unordered chapters

No, but it is under specified. It mentions it should be used with Control Track but that feature has a separate document that we have not started working on yet (and may never will). It can be more precisely defined there if that happens.

How do nested chapters interact with ChapterFlagEnabled?

For now this is not properly specified and should not be used. This is to be decided with the Control Track document, which is possible to build, but not tracked at the IETF as a work in progress document.