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RE: Requirements for external text alternatives for audio/video

From: Sean Hayes <Sean.Hayes@microsoft.com>
Date: Thu, 25 Mar 2010 22:23:56 +0000
To: Silvia Pfeiffer <silviapfeiffer1@gmail.com>, Eric Carlson <eric.carlson@apple.com>
CC: Geoff Freed <geoff_freed@wgbh.org>, HTML Accessibility Task Force <public-html-a11y@w3.org>, Matt May <mattmay@adobe.com>, Philippe Le Hegaret <plh@w3.org>
Message-ID: <8DEFC0D8B72E054E97DC307774FE4B9119EFE38E@DB3EX14MBXC315.europe.corp.microsoft.com>
OK, to be clear I wasn't saying that mapping to CSS is the way things should be done, but only that it is one implementation option. I personally think that the text overlay should be considered as outside of the HTML space in exactly the same way as the video and audio streams are. Captions are a media essence, and have IP rights associated with them. If we integrate the display model into the HTML one, this potentially exposes the caption text to the viewer, and this approach won't work with a protected media file.  

Implementing TTML using a private HTML/CSS stack would be fine, but is as I say, just one implementation option.


-----Original Message-----
From: public-html-a11y-request@w3.org [mailto:public-html-a11y-request@w3.org] On Behalf Of Silvia Pfeiffer
Sent: Thursday, March 25, 2010 8:50 PM
To: Eric Carlson
Cc: Geoff Freed; HTML Accessibility Task Force; Matt May; Philippe Le Hegaret
Subject: Re: Requirements for external text alternatives for audio/video

Hi Eric,

On Fri, Mar 26, 2010 at 2:46 AM, Eric Carlson <eric.carlson@apple.com> wrote:
>
> On Mar 24, 2010, at 9:29 PM, Silvia Pfeiffer wrote:
>
> In summary - I would suggest keeping the File Format requirement at 
> http://www.w3.org/WAI/PF/HTML/wiki/Media_TextAssociations#File_Formats
> with supporting both, srt and dfxp (or ttml as Sean clarified).
>
>   What DFXP profile are you suggesting we mandate?
>   As Maciej noted [1], even the presentation profile requires XSL-FO. 
> Does anyone actually think it is reasonable to require a UA to 
> implement this substantial spec just to style captions?
> eric
> [1] - 
> http://lists.w3.org/Archives/Public/public-html-a11y/2010Mar/0103.html

I believe right now all we need to mandate is the required part of the minimum profile
(http://www.w3.org/TR/ttaf1-dfxp/#profile-dfxp-presentation) - it would conform with WCAG and be extensible to the other features that will certainly be mandated in the future. It looks to me that if other profiles are necessary beyond the ones already given in the TTML specification, these can be developed at a later stage.

Right now we need to take care to find a way to deal with the style and layout specifications. I agree with Sean that this should be done not by implementing the TTML specifications directly, but by mapping them to existing HTML/CSS/JavaScript constructs.


Philippe's demos is at http://www.w3.org/2009/02/ThisIsCoffee.html
with the original TTML file at
http://www.w3.org/2009/02/ThisIsCoffee61_captions.xml and the JavaScript that interprets it at http://www.w3.org/2008/12/dfxp-testsuite/web-framework/HTML5_player.js.
The test suite is at
http://www.w3.org/2008/12/dfxp-testsuite/web-framework/START.html
which demonstrates support (or lack of support) for each TTML feature
- choose the HTML5 player to see what mappings are already supported.

These mappings that are currently done in JavaScript have to be extracted into a specification document. And we need to make sure when we implement support for captions that we can add the features parsed out of TTML into the HTML document.

Cheers,
Silvia.
Received on Thursday, 25 March 2010 22:24:39 GMT

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