Re: In-file style sheets for VTT, discussion

On 11 Mar 2015 18:31, "Thierry MICHEL" <tmichel@w3.org> wrote:
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>
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> On 10/03/2015 22:14, David Singer wrote:
>>
>> WARNING WARNING:  email sent to both the Community Group and the Working
Group.  You might wish to trim your response.
>>
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>> Friends, colleagues
>>
>> VTT has been in a fairly quiet ‘implement and fix bugs and other
inclarities in the spec.’ mode, but there is one feature request that came
up while we are getting wide review of the spec as a result of the FPWD.
>>
>> The question came up actually when we were first designing VTT, but we
shelved it until now.  The request is to make it possible to provide
styling in the VTT file.
>>
>> At the moment, both the technical discussion (how do to it) and the
process discussion (should we do it in this version or the next) are
happening in the bug tracker:
>>         https://www.w3.org/Bugs/Public/show_bug.cgi?id=15023
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>> While I hate it when conversations happen in two or three places, I want
to be sure that all members of both groups are aware of both aspects of
this conversation and have a chance to make their opinions known, on the
needs, on the design, on the timing, and so on.
>>
>> Obviously comments on the bug would be welcome, but follow-ups to either
the CG or WG would be fine also.  I’ll try to make sure everyone sees at
least the Best Bits of any Relevant Conversation :-)
>>
>>
>> On the process, I am cautious about introducing a feature when we want
to go to CR, but on the other hand, I don’t see any point in asking for a
CR transition if the response to that request will be the statement from
the community that this feature is missing.  It’s useful, envisioned for a
long time, and can be done in a clean way, I think.
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> We may have other requests from the accessibility, I18N folks before
going to CR. Let's wait for the wide review from the groups for which the
TTWG has dependencies with.
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> For the styling in WebVTT, the major use case I see is that currently a
WebVTT can be only styled in an HTML browser media player (the CCS style
being declared in the HTML hosting page).
> Therefore a WebVTT file can not be played styled in a none HTML Media
player.
> To allow this, adding CSS styling within WebVTT file would satisfy that
need. Web browsers could also parse WebVTT file styling.
>

Yes, that's a good summary of the motivation for this feature.

> Also providing a CSS styling within WebVTT file resolves some
accessibilities issues, if the users needs to change the default styling
(bigger fonts, diffrent colors, etc...)
>

Not really, because such styling would be supplied power user through
browser settings so they would overrule CSS styling.

> CSS stylings in the WebVTT file can be done as follows:
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> 1-In the Header:
>
> 1.1- Import a CSS style sheet:
>     Style:
>       @import(cea608.css)
>     ##
>
> 1.2- In a  CSS style declaration section:
>     WEBVTT
>       Style:
>       ::cue(v[voice=Bob]) {color:green;}
>       ::cue(c.question) {font-style:italic;}
>     ##
>

There's a bit more detail in the bug that David referenced. Again: if there
are technical concerns, I would encourage discussion to continue in the
bug, so it status together as much as possible.

> 2- Inline styling (throughout the WebVTT file not just in the header of a
WebVTT file). Possibly even scoped for individual cues -

This use case was rejected by Apple, so as to avoid having to keep track of
such temporary changes during the duration of the video and enable direct
access ability, in particular in in-band or hls used of WebVTT.

I think that's fair, since we have this:

> Note: Currently there is support per-cue styling via cue IDs (but not yet
implemented).
>     <style>  ::cue(#myid) {font-style : italic;}  </style>

It's implemented in chrome and safari, just not in Firefox or IE.

Cheers,
Silvia.

> Thierry
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>> Thanks
>>
>> David Singer
>> Manager, Software Standards, Apple Inc.
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>