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Re: [media] Moving forward with captions / subtitles

From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Date: Sat, 20 Feb 2010 16:22:13 +1100
Message-ID: <2c0e02831002192122j50bac456s825de4cacaebfea6@mail.gmail.com>
To: David Singer <singer@apple.com>
Cc: John Foliot <jfoliot@stanford.edu>, philipj@opera.com, Eric Carlson <eric.carlson@apple.com>, Geoff Freed <geoff_freed@wgbh.org>, HTML Accessibility Task Force <public-html-a11y@w3.org>
On Sat, Feb 20, 2010 at 5:45 AM, David Singer <singer@apple.com> wrote:
> On Feb 18, 2010, at 19:13 , Silvia Pfeiffer wrote:
>> I am not sure there if MP4 allows to set a track as enabled (or
>> provides such a hint to the media players).
> Yes, the track enable bit, and also track alternates (really alternatives) are both in MP4.  I think this is a natural way to bundle media -- put the optional features in tracks that get enabled on demand.  My current naive thinking is that a media query might again help here.

No, not necessary. It's all already exposed in the JavaScript API and
the external captions work exactly the same. Thus, the media engine
just has to hand this information on to the browser for state and tell
the browser to do the right things with these.

> On Feb 18, 2010, at 21:56 , Silvia Pfeiffer wrote:
>> On Fri, Feb 19, 2010 at 4:49 PM, Eric Carlson <eric.carlson@apple.com> wrote:
>>>  I am in favor of using the same model we have with <source> - the content author "describes" each alternate with attributes and the UA picks the first one that is appropriate for the user's preferences and machine environment.
>> I agree. I think it's basically what I have described here:
>> http://www.w3.org/WAI/PF/HTML/wiki/Media_TextAssociations#Resource_selection_algorithm
>> . Let me know if that captures it.
> seems it would be more natural to say if a track is in a trackgroup, that it is enabled if the trackgroup is enabled.
> example.  I think I want to write:
> <trackgroup media="accessibility(captions:yes") >
>  <track src="fr.srt" lang="fr"/>
>  <track src="de.srt" lang="de" />
> </trackgroup>
> and not
> <trackgroup  >
>  <track src="fr.srt" lang="fr" media="accessibility(captions:yes")/>
>  <track src="de.srt" lang="de" media="accessibility(captions:yes") />
> </trackgroup>
> and certainly not
> <trackgroup  >
>  <track src="fr.srt" lang="fr" media="accessibility(captions:yes")/>
>  <track src="de.wav" lang="de" media="accessibility(audiodescription:yes") />
> </trackgroup>
> since the semantics of trackgroup is exclusive; surely therefore the "do you want it at all" question applies only ever to the whole group?

You can never be sure that the question only applies to one track
group. There can be captions inside the media file and there can be
captions in tracks outside the trackgroup.

BTW: your markup above is already possible, since the media attribute
can be used both on a trackgroup (for shortness) or on each element
separately. It just doesn't necessarily speak for the whole
trackgroup. And ... the role attribute gives you the information that
your accessibility media query currently provides. The way that media
queries work is more about what your display device is able to

Received on Saturday, 20 February 2010 05:23:06 UTC

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