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

Re: timing model of the media resource in HTML5

From: Philip Jägenstedt <philipj@opera.com>
Date: Wed, 25 Nov 2009 21:02:19 +0100
To: "Eric Carlson" <eric.carlson@apple.com>
Cc: "Silvia Pfeiffer" <silviapfeiffer1@gmail.com>, "HTML Accessibility Task Force" <public-html-a11y@w3.org>
Message-ID: <op.u3yu95tosr6mfa@worf>
On Wed, 25 Nov 2009 18:43:39 +0100, Eric Carlson <eric.carlson@apple.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/subtitles:
>      <video src='my-captioned-movie'> </video>

Yes, that sounds good. One issue is how to style such an implicit  
<overlay>. Should one actually include an <overlay> in the markup and  
somehow indicate that it can/should be used to render in-band subtitles  
 from the resource?

<video src="my-captioned-movie">
   <caption style="font-weight:bold" magic-attribute></caption>

Not awesome. Perhaps a new CSS pseudo-selector could be used? Other ideas?

Philip Jägenstedt
Opera Software
Received on Wednesday, 25 November 2009 20:01:43 UTC

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