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 23:49:47 +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.u3y209wnsr6mfa@worf>
On Wed, 25 Nov 2009 22:49:40 +0100, Eric Carlson <eric.carlson@apple.com>  

> On Nov 25, 2009, at 12:02 PM, Philip Jägenstedt wrote:
>> On Wed, 25 Nov 2009 18:43:39 +0100, Eric Carlson <eric.carlson@apple.com 
>> > wrote:
>>>   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>
>> </video>
>> Not awesome. Perhaps a new CSS pseudo-selector could be used? Other  
>> ideas?
>    Actually I was imagining that *all* subtitles and captions, in-band  
> and external alike, would be rendered into an <overlay>. If the markup  
> doesn't includes an <overlay> element the UA would actually insert one  
> into the DOM, as is done now for other missing elements (eg. tbody,  
> etc). This way the default style could be specified in the user agent  
> style sheet and the author could override as they wish.

Right, all subtitles/captions should be rendered in <overlay> regardless  
of origin. If the parser automatically inserts an <overlay> element when  
there is none, what about the case where there is an <overlay> used to  
show custom controls? I imagined the need for a magic attribute/CSS  
selector/something to point out the correct <overlay> in cases like this.  
Possibly a magic src attribute? In any case, these are small issues that  
I'm sure could be sorted out if <overlay> is implemented.

>    Speaking of author overrides, another issue we need to deal with is  
> authors that wish to handle captions themselves. Posting an event when a  
> new caption needs to be displayed seems logical enough, but how do we  
> provide access to the caption data in JavaScript?

Here I think we should do something similar to cue ranges as has been  
discussed before in various places. A new event type would allow us to add  
some data, e.g.

interface CueRangeEvent : Event {
   readonly attribute double startTime;
   readonly attribute double endTime;
   readonly attribute DOMString text;

We would need to bring back addCueRange with some modifications.

v.addCueRange(10 /* start */, 12 /* end */, "Hello");
v.addEventListener('cuerangeenter', function(e) {  
e.target.querySelector('overlay').textContent = e.text; }, false);
v.addEventListener('cuerangeleave', function(e) {  
e.target.querySelector('overlay').textContent = ''; }, false);

You get the idea even if the above doesn't have the perfect  
interface/method/event names. Something along these lines should make it  
possible to handle in-band, external and script-created captions in a  
quite uniform fashion, as well as provide for whatever use cases the old  
cue range API had.

Philip Jägenstedt
Core Developer
Opera Software
Received on Wednesday, 25 November 2009 22:49:22 UTC

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