[Bug 26921] [InbandTracks] DASH trackId

https://www.w3.org/Bugs/Public/show_bug.cgi?id=26921

--- Comment #3 from Bob Lund <b.lund@cablelabs.com> ---
(In reply to Cyril Concolato from comment #2)
> (In reply to Bob Lund from comment #1)
> > (In reply to Cyril Concolato from comment #0)
> > > "Content of the 'id' attribute in the AdaptationSet or ContentComponent
> > > element. Empty string if 'id' attribute is not present."
> > > 
> > > The AdaptationSet@id is not unique within an MPD, but within a Period. The
> > > Period@id is unique within an MPD, even after MPD updates. Similarly, the
> > > ContentComponent@id is unique only within the AdaptationSet. Additionally,
> > > it is not clear how representations are exposed.
> > 
> > HTML audio, video and text tracks should correspond to DASH AdaptationSet or
> > ContentComponent. Different Representations within an AdaptionSet aren't
> > different HTML tracks.
> Why not? In GPAC we expose all representations in our UI, for instance to
> select a representation when Adaptive Bitrate Switching is off.


In the case of MSE, there is no need for representations as tracks. The Web app
already has access to all representations and can switch or not among
representations in an AS.

There is no defined HTML API for the Web app to determine when ABR switching is
off if the UA implements MPD processing and representation switching. Further,
representation switching by enabling/disabling video tracks is not going to
result in seamless switching.

> 
> > The DASH spec also requires (section 5.3.3.1) that all Representations in an
> > AdaptationSet have the same values for attributes that are used to set HTML
> > track @kind, @language and @label.
> Not exactly. We define how the @kind, @language and @label are generated
> from the MPD. We could decide to add the bandwidth value in the label in
> that case, or in a separate attribute.
> 
> > > I'd suggest using the triplets (Period@id, AdaptationSet@id,
> > > Representation@id (or ContentComponent@id) to generate an id for the track.
> > > It may be useful to use the MPD fragment identifiers for that but I'm not
> > > sure we can address representations or sub-representations properly.
> > 
> > Seems like (Period@id, AdaptationSet@id [, ContentComponent@id]).
> In a first or minimal approach, yes. I agree.

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Received on Tuesday, 14 October 2014 19:39:39 UTC