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RE: Track fragments

From: Davy Van Deursen <davy.vandeursen@ugent.be>
Date: Wed, 17 Feb 2010 15:49:38 +0100
To: 'RaphaŽl Troncy' <raphael.troncy@eurecom.fr>
Cc: "'Silvia Pfeiffer'" <silviapfeiffer1@gmail.com>, "'DENOUAL Franck'" <Franck.Denoual@crf.canon.fr>, <public-media-fragment@w3.org>
Message-ID: <005901caafe0$6e5fd5f0$4b1f81d0$@vandeursen@ugent.be>
On feb 17, 2010 at 15:14, RaphaŽl Troncy wrote:
> Cc: 'Silvia Pfeiffer'; 'DENOUAL Franck'; public-media-fragment@w3.org
> Subject: Re: Track fragments
> >> Why do you use 'tracks' instead of 'track'?
> >> What prevent you to use: #track='track1'&track='track2'?
> >
> > Because that might not be compliant to our grammar :-)?
> Well, we don't consider 'tracks' with an 's' either in the grammar :-)
> We have discussed in today's telecon that we would not like to allow 
> something like: <uri>#t=30,90&t=10,15. More generally, we don't want 
> that the time or the space dimension is specified more than once in 
> the fragment because we don't want to bother trying to understand what 
> does it mean. The question remains for the track dimension, since it 
> is reasonable to restrict a media file to a number of tracks.
> I see (at least) two points to resolve:
>    - What are the changes we need to make (if any) in the grammar to 
> allow a selection of multiple tracks in a fragment? Silvia has proposed:
> #track="audio(audesc,en);video(main,en);text(cc,en);text(sub,fr)" ... 
> a semi-colon separator
>    - What is the semantics of the fragment when one or multiple tracks 
> is specified in a fragment? Does it mean *only* the tracks selected 
> explicitly in the fragment? In other words:
> #track="audio(audesc,en);text(sub,fr);" will not contain video but 
> just an audio and subtitle tracks?

Just a small detail regarding the grammar proposal: I would write each track
name between single quotes: #track='audio(audesc,en)';'video(main,en)' ...

Regarding your second point, my feeling is that only the tracks specified in
a fragment should be selected. Otherwise, it is not clear to me which tracks
should be send 'implicitly' to the UA.

> > The only reason was
> > that I wanted to keep the identifiers currently specified by the
> group
> > as they were. That can be easily changed of course, it's just a
> matter
> > of syntax sugar I guess. As a side note, similar to 'tracks', we 
> > also have the 'ts' identifier which can be used to identify more 
> > than one time range (e.g., #ts=0,10;20,30) but I think multiple time 
> > ranges is less relevant for us right now.
> And what does it mean? Is it an union? An intersect? An incluion (out 
> of range in this case)?

It is a union of the specified time fragments. So the example ?ts=0,10;20,30
(note the change of # to ?, because this only works through query
identifiers) will result in a resource with a duration of approximately 20

Best regards,


Davy Van Deursen

Ghent University - IBBT
Department of Electronics and Information Systems - Multimedia Lab
URL: http://multimedialab.elis.ugent.be/dvdeurse
Received on Wednesday, 17 February 2010 14:49:38 UTC

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