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Re: Proposed extension to HTML5.1 for rollup captions

From: Glenn Adams <glenn@skynav.com>
Date: Thu, 21 Feb 2013 07:05:51 -0700
Message-ID: <CACQ=j+dU0an6Zi65NmXkbdwXf7aQReaJryBFSR2U9E3X9O=dhA@mail.gmail.com>
To: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Cc: Travis Leithead <travis.leithead@microsoft.com>, "public-html@w3.org" <public-html@w3.org>, public-tt <public-tt@w3.org>
On Thu, Feb 21, 2013 at 1:37 AM, Silvia Pfeiffer
<silviapfeiffer1@gmail.com>wrote:

> On Thu, Feb 21, 2013 at 7:23 PM, Silvia Pfeiffer <
> silviapfeiffer1@gmail.com> wrote:
>
>> Hi Glenn,
>>
>> On Thu, Feb 21, 2013 at 9:52 AM, Glenn Adams <glenn@skynav.com> wrote:
>>
>>>
>>> On Wed, Feb 20, 2013 at 1:46 PM, Travis Leithead <
>>> travis.leithead@microsoft.com> wrote:
>>>
>>>> > From: Silvia Pfeiffer [mailto:silviapfeiffer1@gmail.com]
>>>> >
>>>> > I'm looking for feedback on this feature here. If there are no
>>>> objections
>>>> > and sufficient support for these features, I suggest adding them to
>>>> the
>>>> > HTML5.1 specification.
>>>>
>>>> I'm very cautious about immediately merging this feature back into
>>>> HTML5.1. I believe the best course of action is to keep this feature
>>>> separate from the HTML5.1 spec (as a stand-alone document) as it allows
>>>> easier review, as well as time to get consensus and develop the proposal
>>>> based on feedback.
>>>>
>>>> Given that there is some time elapsed between now and when you can get
>>>> sufficient support, then I don't object to merging it in. I would prefer to
>>>> have at least a month or two to have time to gather all the right people
>>>> together, perform the review, summarize and submit (and have time for you
>>>> to incorporate any feedback).
>>>>
>>>> Finally, just a quick "thank you" for putting this together. I really
>>>> like that extension specs are starting to be developed and I want to
>>>> encourage folks to continue to submit these and get them started as
>>>> reviewable documents.
>>>>
>>>
>>> A few questions of clarification:
>>>
>>>    - does this rollup caption extension depend on
>>>    https://dvcs.w3.org/hg/text-tracks/raw-file/default/608toVTT/region.html? if the answer is yes, then these TextTrackRegion interface extensions
>>>    need to be renamed to WebVTTTextTrackRegion or otherwise made more generic
>>>    to accommodate use of TTML instead of WebVTT
>>>
>>>
>> No, they don't depend on WebVTT. It's a generic concept that builds on
>> CEA708 windows and should thus similarly be able to present TTML rollup
>> captions.
>>
>>
>>>
>>>    - does the mechanisms defined as extensions to the current HTML5
>>>    TextTrack and related interface types take into account use of TTML instead
>>>    of WebVTT? if the answer is no, then it should be reviewed and modified as
>>>    needed to permit use of TTML as well, or at least support future
>>>    integration with TTML
>>>
>>>
>> Yes, it does just as much as TextTrackCue also permits use of TTML. I
>> actually mentioned that in my email, but maybe not explicitly enough.
>>
>>
>>>
>>> Overall, we need to keep in mind that TTML will be used by commercial
>>> video content providers for captioning HTML5 media elements,
>>>
>>
>
> On a somewhat unrelated side note: while the industry is starting to use
> TTML, only IE10 has released basic support for it in <track>.
>

I expect to see wider support for TTML in browsers in the relatively near
future, and have started looking into adding support in WK.


>  In contrast, all browsers are implementing support for WebVTT (including
> IE10). Since it's explicitly stated that TTML is created for *the purpose
> of interchange among authoring systems*, while WebVTT is created for
> rendering in browsers, it may be worthwhile to start creating a mapping
> between TTML and WebVTT. I'd be happy to help.
>

To give a bit more context, TTML also states "In addition to being used for
interchange among legacy distribution content formats, TTML content may be
used directly as a distribution format" so it certainly isn't limited to
authoring interchange. Given the recent FCC designation of TTML as a safe
harbor format for caption delivery over the Internet, I expect its usage as
a direct distribution format to increase.

In any case, I support defining a mapping between TTML and WebVTT to the
extent that is feasible. It would probably be useful to start with the TTML
SDP-US profile published recently at [1].

[1] http://www.w3.org/TR/2013/NOTE-ttml10-sdp-us-20130205/


> Since the WebVTT extension that we are pursuing in the Community Group
> will introduce means for authoring rollup captions in WebVTT, and the
> TextTrackRegion provides the rendering means in the browser, the region
> feature should fill the gaps that previously existed for the FCC required
> caption features and thus for TTML conversion.
>

I will suggest to the TTWG to review this work as well, as there may be
some additional input coming from TTML applications of these interfaces.

Perhaps we should start a new thread on <public-tt@w3.org> to pursue this
further.

Regards,
Glenn
Received on Thursday, 21 February 2013 14:06:47 GMT

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