W3C home > Mailing lists > Public > public-html-a11y@w3.org > December 2010

RE: [media] handling multitrack audio / video

From: Sean Hayes <Sean.Hayes@microsoft.com>
Date: Fri, 3 Dec 2010 14:02:48 +0000
To: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
CC: Philip Jägenstedt <philipj@opera.com>, Eric Carlson <eric.carlson@apple.com>, Geoff Freed <geoff_freed@wgbh.org>, "HTML Accessibility Task Force" <public-html-a11y@w3.org>, Frank Olivier <Frank.Olivier@microsoft.com>
Message-ID: <8DEFC0D8B72E054E97DC307774FE4B91330C378E@DB3EX14MBXC315.europe.corp.microsoft.com>
Well the difference is being able to have groups of sources; but yes linear selection might not be ideal.
I agree an external manifest may well the best way to go to get all of this complexity out of HTML5, including the video format issue. Possibly the mooted new WG could also address standardizing a manifest.

HTML5 could then get back to just:
<media src="manifest.moo"/>

I suspect it's a little late in the day for that though.

-----Original Message-----
From: Silvia Pfeiffer [mailto:silviapfeiffer1@gmail.com] 
Sent: 03 December 2010 13:24
To: Sean Hayes
Cc: Philip Jägenstedt; Eric Carlson; Geoff Freed; HTML Accessibility Task Force; Frank Olivier
Subject: Re: [media] handling multitrack audio / video

Hmm... now we just need to throw the alternatives in webm and mp4 as well as ogg format into this...

Incidentally, according to
http://www.w3.org/TR/2005/REC-SMIL2-20050107/smil-content.html#q5 , the <switch> element also just takes the first acceptable element, which is no different to the way in which <source> works. We probably would want to redefine that to pick the most appropriate one rather than the first acceptable one.

I'm hoping we can find a simpler markup though, to be honest.

Right now I am trying to think out of the box - how about considering something like a manifest file that would simply list all the available alternatives with their uses similar to a m3u8 file. This would probably be just for one per format (ogg/webm/mp4) and in would be nice if the browser decided which one to take.


On Fri, Dec 3, 2010 at 10:14 PM, Sean Hayes <Sean.Hayes@microsoft.com> wrote:
> Well at the risk of channeling Dick Bulterman:
>  <...>
>      <switch syncmaster >  <!-- this element selected from this group 
> provides the timing -->
>         <video src=" mainMovieOC.ogg " systemSubtitle  
> systemLanguage="zh-Hant"  ... />   <!-- this has open subtitles in 
> trad chinese-->
>         <video src="mainMovie.ogg" ... />   <!-- the default with no 
> constraints -->
>    </switch>
>      <switch>
>         <video src=" transMovieBSL.ogg " systemLanguage="sgn-GB"  ... 
> />   <!-- a BSL sign language translation to be synced to the main 
> movie-->
>         <video src="transMovieASL.ogg" systemLanguage="sgn-US"   ... 
> />   <!-- an ASL sign language translation to be synced to the main 
> movie -->
>    </switch>
>     <switch>
>      <audio src="mainMovie.en.mp3" systemAudioDesc systemLanguage="en" 
> ... />   <!-- alternate described soundtracks in a variety of 
> languages -->
>      <audio src="mainMovie.nl.mp3" systemAudioDesc systemLanguage="nl" 
> ... />
>      <audio src="mainMovie.de.mp3" systemAudioDesc  
> systemLanguage="de"  ... />
>    </switch>
>    <switch>
>       <text src="movie-sub-en.rtx" systemLanguage="en  systemCaptions 
> ... /> <!-- alternate text tracks for subtitles and captions -->
>       < text src="movie-sub-de.rtx" systemLanguage="de" systemSubtitle 
> ... />
>       < text src="movie-sub-nl.rtx" systemLanguage="nl" systemSubtitle  
> ... />
>    </switch>
>  </...>
> You might need to shuffle things around a bit to fit in HTML, and you could replace the systemXXX attributes with media queries.
> -----Original Message-----
> From: public-html-a11y-request@w3.org 
> [mailto:public-html-a11y-request@w3.org] On Behalf Of Philip 
> Jägenstedt
> Sent: 03 December 2010 10:01
> To: Silvia Pfeiffer; Eric Carlson
> Cc: Geoff Freed; HTML Accessibility Task Force; Frank Olivier
> Subject: Re: [media] handling multitrack audio / video
> On Thu, 02 Dec 2010 16:41:56 +0100, Eric Carlson 
> <eric.carlson@apple.com>
> wrote:
>> On Dec 2, 2010, at 6:31 AM, Silvia Pfeiffer wrote:
>>> For #3 there is not much to do actually - just having a means to 
>>> switch between resources would be sufficient. That means could be a 
>>> button underneath the video or a second tab with the video and lets 
>>> the user change between the main video and it's auditory-only 
>>> counterpart. I wonder if we even need special accessibility features 
>>> for this.
>> The idea we have long talked about to use media queries on a <source> 
>> element to label the accessibility features of its resource could be 
>> very useful here. It would allow an author to include videos with and 
>> without open audio descriptions in the markup:
>>    <video controls>
>>        <source src="trailer_with_open_captions.m4v"
>> media="accessibility(audiodescription:yes)" >
>>        <source src="trailer.m4v">
>>    </video>
>> and the user agent will automatically choose the captioned file if 
>> the user's preferences say they want them.
> Anything that overloads <source> will suffer from the problem that 
> users can't switch between versions once one has been selected. The 
> resource selection algorithm is already quite messy. Today, <source> 
> is supposed to be used for equivalent resources where only the format 
> differs. For alternative tracks, I think we really need something 
> different. I'd say <track>, but that's really for *additional* tracks 
> so far, not alternatives...
> --
> Philip Jägenstedt
> Core Developer
> Opera Software
Received on Friday, 3 December 2010 14:03:56 UTC

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