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Re: timing model of the media resource in HTML5

From: Eric Carlson <eric.carlson@apple.com>
Date: Wed, 25 Nov 2009 08:01:27 -0800
Cc: Silvia Pfeiffer <silviapfeiffer1@gmail.com>, HTML Accessibility Task Force <public-html-a11y@w3.org>
Message-Id: <0B3467C6-D8B2-436E-B380-6769149DC2C5@apple.com>
To: Philip Jägenstedt <philipj@opera.com>

On Nov 25, 2009, at 4:24 AM, Philip Jägenstedt wrote:

> I agree that syncing separate video and audio files is a big challenge. I'd prefer leaving this kind of complexity either to scripting or an external manifest like SMIL.
> 

  +1 to keeping multiple element synchronization out of our spec!


> Below I focus on the HTML-specific parts:
> 
> Captions/subtitles... The main problem of reusing <source> is that it doesn't work with the resource selection algorithm.[1] However, that algorithm only considers direct children of the media element, so adding a wrapping element would solve this problem and allow us to spec different rules for selecting timed-text sources. Example:
> 
> <video>
>  <source src="video.ogg" type="video/ogg">
>  <source src="video.mp4" type="video/mp4">
>  <overlay>
>    <source src="en.srt" lang="en-US">
>    <source src="hans.srt" lang="zh-CN">
>  </overlay>
> </video>
> 
> We could possibly allow <overlay src="english.srt"></overlay> as a shorthand when there is only one captions file, just like the video <video src=""></video> shorthand.
> 
> I'm suggesting <overlay> instead of e.g. <itext> because I have some special behavior in mind: when no (usable) source is found in <overlay>, the content of the element should be displayed overlayed on top of the video element as if it were inside a CSS box of the same size as the video. This gives authors a simple way to display overlay content such as custom controls and complex "subtitles" like animated karaoke to work the same both in normal rendering and in fullscreen mode. (I don't know what kind of CSS spec magic would be needed to allow such rendering, but I don't believe overlaying the content is very difficult implementation-wise.)
> 
  I like the idea of an <overlay> element, but I don't understand what you are proposing for when no usable source is found. Can you elaborate please?


> If there is a use case, displaying several captions/subtitles at once could be allowed as such:
> 
> <video src="video.ogg">
>  <overlay src="en.srt" class="centerTop"></overlay>
>  <overlay src="hans.srt" class="centerBottom"></overlay>
> </video>
> 
  I also like this idea. I don't think it will be difficult to find legitimate use cases, eg. displaying closed captions and subtitles simultaneously.

eric
Received on Wednesday, 25 November 2009 16:02:01 GMT

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