W3C home > Mailing lists > Public > public-html-a11y@w3.org > November 2009

Re: timing model of the media resource in HTML5

From: Eric Carlson <eric.carlson@apple.com>
Date: Wed, 25 Nov 2009 09:43:39 -0800
Cc: Silvia Pfeiffer <silviapfeiffer1@gmail.com>, HTML Accessibility Task Force <public-html-a11y@w3.org>
Message-id: <BC01FD34-0B84-4B68-B3C6-8F9D30E9F9A1@apple.com>
To: Philip Jägenstedt <philipj@opera.com>

On Nov 25, 2009, at 8:50 AM, Philip Jägenstedt wrote:

> On Wed, 25 Nov 2009 17:01:27 +0100, Eric Carlson <eric.carlson@apple.com 
> > wrote:
>> On Nov 25, 2009, at 4:24 AM, Philip Jägenstedt wrote:
>>> 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?
> My thinking is that <overlay> should be the container of overlay  
> content whether it is from an external subtitle file or from HTML.  
> When an external subtitle file is used the element acts as if it had  
> a single text node child with the content of the current text from  
> the subtitle file.
> In the absence of an external file the content of the element is  
> shown as "fallback", which can then easily be set using script.
   Thanks, that makes sense.

   I think <overlay> should be used for internal subtitle and/or  
closed caption tracks as well. Further, I think that we will want them  
to "just work" so a UA should create an <overlay> element if the  
markup doesn't have one and it finds that a file has internal captions/ 

     <video src='my-captioned-movie'> </video>

Received on Wednesday, 25 November 2009 17:44:12 UTC

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