[whatwg] Introduction of media accessibility features

Maciej Stachowiak mjs at apple.com
Sun Apr 11 21:47:37 PDT 2010

On Apr 11, 2010, at 2:59 PM, Jonas Sicking wrote:

> On Sun, Apr 11, 2010 at 5:30 AM, Silvia Pfeiffer
> <silviapfeiffer1 at gmail.com> wrote:
> f>> Is it expected that all of TTML will be required? The proposal  
> suggests
>> That is also something that still has to be discussed further.  
>> Initial
>> feedback from browser vendors was that the full TTML spec is too
>> complicated and too much to support from the start. Thus, the
>> implementation path with the TTML profiles is being suggested.
>> However, it is as yet unclear if there should be a native parsing
>> implementation of TTML implemented in browsers or simply a mapping of
>> TTML markup to HTML/CSS/JavaScript. My gut feeling is that the latter
>> would be easier, in particular since such a mapping has been started
>> already with Philippe's implementation, see
>> http://www.w3.org/2009/02/ThisIsCoffee.html . The mapping would need
>> to be documented.
> Personally I'm concerned that if we start heading down the TTML path,
> browsers are ultimately going to end up forced to implement the whole
> thing. Useful parts as well as parts less so. We see this time and
> again where if we implement part of a spec we end up forced to
> implement the whole thing.

I'm especially concerned that TTML presentation is formally defined in  
terms of XSL-FO, itself an extremely complicated spec that is in many  
ways at odds with the CSS formatting model in browser engines. I am  
not at all enthusiastic about implementing a second layout engine just  
for captions.

While some have claimed that it's probably possible to translate TTML  
presentation requirements to CSS, I don't really buy this without  
seeing a normative specification for how to do so.


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