[Bug 26716] [InbandTracks] Track order

https://www.w3.org/Bugs/Public/show_bug.cgi?id=26716

--- Comment #5 from Bob Lund <b.lund@cablelabs.com> ---
(In reply to Cyril Concolato from comment #4)
> I was considering only container formats and so far MP4, MPEG-2 TS, WebM and
> Ogg, all have an id for tracks. DASH AdaptationSets indeed may not always
> have an id, but I don't think you want to rely on videoTracks[3] to be the
> third AdaptationSet in the MPD because the MPD may have been filtered in the
> network, or rewritten by an XML processor and there is no guarantee that the
> order has been preserved.

What does "no guarantee that the order has been preserved" mean? The order is
whatever is present in the MPD when the UA parses it. It is irrelevant what the
MPD state was before the UA gets it. In any case, what is the alternative?
Create the tracks in a random order? Would this benefit the application?

This part of the spec is not a suggestion that the application should rely on
track order. It is a response to the HTML spec statement "Tracks in
AudioTrackList and VideoTrackList objects must be consistently ordered. If the
media resource is in a format that defines an order, then that order must be
used; otherwise, the order must be the relative order in which the tracks are
declared in the media resource. The order used is called the natural order of
the list."

Applications can use the track.id attribute if it is set.

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Received on Thursday, 25 September 2014 16:27:24 UTC