[whatwg] Introduction of media accessibility features

Silvia Pfeiffer silviapfeiffer1 at gmail.com
Sun Apr 11 23:39:14 PDT 2010

On Mon, Apr 12, 2010 at 4:00 PM, Philip Jägenstedt <philipj at opera.com> wrote:
> On Mon, 12 Apr 2010 08:47:33 +0800, Silvia Pfeiffer
> <silviapfeiffer1 at gmail.com> wrote:
>> On Mon, Apr 12, 2010 at 7:59 AM, Jonas Sicking <jonas at sicking.cc> 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
>>>>> 'starting with the simplest profile', being the transformation profile.
>>>>> Does
>>>>> this mean only the transformation profile is needed to provide subtitle
>>>>> features equivalent to SRT?
>>>> 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.
>>> Things like test suites, blogging advocates, authoring tools, etc
>>> often means that for marketing reasons we're forced to implement much
>>> more than we'd like. And much more than is useful. This is why spec
>>> writing is a big responseibility, every feature has a large cost and
>>> means that implementors will be working on implementing that feature
>>> instead of something else.
>> Understood. But what is actually the cost of implementing all of TTML?
>> The features in TTML all map onto existing Web technology, so all it
>> takes is a bit more parsing code over time. And if we chose not to
>> implement TTML, we will have to eventually support some other format
>> that provides formatting and positioning capabilities, seeing how the
>> legal landscape has evolved for traditional media (e.g. TV, set-top
>> box technology). Since TTML was originally developed to be the
>> exchange format for all such formats, it should have a sensible set of
>> features for this space. So, I personally think it's not a bad choice
>> for the purpose. Which other format did you have in mind to replace
>> it?
> For the record, I am also not enthusiastic about TTML, specifically the
> styling mechanism which even makes creative use of XML namespaces. An
> example [1] for those that haven't seen it before:
> <region xml:id="r1">
>  <style tts:extent="306px 114px"/>
>  <style tts:backgroundColor="red"/>
>  <style tts:color="white"/>
>  <style tts:displayAlign="after"/>
>  <style tts:padding="3px 40px"/>
> </region>
> ...
> <p region="r1" tts:backgroundColor="purple" tts:textAlign="center">
>  Twinkle, twinkle, little bat!<br/>
>  How <span tts:backgroundColor="green">I wonder</span> where you're at!
> </p>
> While I don't have any suggestions about what to use instead, I'd much
> prefer something which just uses CSS with the same syntax we're all used to.
> [1]
> http://www.w3.org/TR/ttaf1-dfxp/#style-attribute-backgroundColor-example-1

I have looked at alternative formats the provide styling and
positioning functionality. There is, for example, ASS/SAA
http://www.matroska.org/technical/specs/subtitles/ssa.html . We could
decide to support something like that instead, but it would be
essentially the same work as for TTML: define a mapping to Web
technologies (HTML, CSS, JavaScript) and implement that mapping, as I
don't think anyone would implement SSA natively either.

I am myself not excited by the way that TTML turned out and would have
wished for a more Web-friendly format to have come out of the W3C, but
that's what it is now. Also, I am really missing hyperlinking
functionality in it, but believe it is possible to extend it in the

We could, of course, decide to develop a totally new specification,
but then we are left on our own to push that into the world. At least
TTML already has support by several existing vendors in the caption
space (see e.g.

I just think of all the options available TTML is the least
problematic way to go. But if somebody has a better idea, I'm more
than open to it! (This is me personally saying it - it's not a
representative opinion of the W3C HTML5 accessibility task force).


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