W3C home > Mailing lists > Public > public-texttracks@w3.org > September 2012

Re: Yet Another Scroll-Up Idea (YASUI) in VTT

From: Simon Pieters <simonp@opera.com>
Date: Fri, 21 Sep 2012 08:47:46 +0200
To: "Silvia Pfeiffer" <silviapfeiffer1@gmail.com>
Cc: public-texttracks <public-texttracks@w3.org>, "David Singer" <singer@apple.com>
Message-ID: <op.wky3twknidj3kv@device-23f190>
On Fri, 21 Sep 2012 03:25:12 +0200, Silvia Pfeiffer  
<silviapfeiffer1@gmail.com> wrote:

> It's  a bit outdated and replaced by
> http://dvcs.w3.org/hg/text-tracks/raw-file/default/608toVTT/608toVTT.html
>  now. I have emailed the group about this before and asked if it can
> become part of what we're working on.

The style sheet looks wrong. You should drop the "video track" from all  
selectors. Also this ruleset seems mostly wrong:

video track {
   font-family: monospace;
   font-size: 100%;
   font-style: normal;
   font-weight: normal;
   font-effect: none;
   background-color: black;
   color: white;
   line-height: 100%;
   position: absolute;
   top: 10%;
   left: 10%;
   width: 80%;
   height: 80%;

The selector should be just ::cue (matches the WebVTT root), there's no  
font-effect property, position, top, left, width and height do not apply  
to WebVTT elements.

Are you sure you want font-size:100%? IIRC it will inherit the font size  
of the video element (which is likely to be 16px or so; won't scale with  
the video). The default is 5vh i.e. 5% of the video viewport's height.

>> Why can't such UAs just support the subset of CSS that they want to  
>> support,
>> like 'color' and 'background-color'? WebVTT already subsets which CSS
>> properties apply, so full CSS support is not needed for WebVTT. Sure,  
>> you
>> need a CSS parser, but that's pretty easy and even has a state machine
>> tokenizer and parser spec now. http://dev.w3.org/csswg/css3-syntax/
> That spec was created for offline players in particular. The default
> CSS style sheet is not one that I would bake into the browsers, but
> one that I would supply the browser with when given a WebVTT file that
> uses 608 features. Thus, from the browser's point of view nothing
> changes.

If offline players support it, and content authors start publishing  
subtitles with these classes but without a style sheet, browsers are  
likely to feel pressured into supporting the classes.

I think we should aim for interoperability, which is to say, an author  
should be able to author an arbitrary WebVTT file, test it in any WebVTT  
UA, and have it work the same everywhere. If that means everyone need a  
default style sheet, fine, but at that point, maybe we should use <font>  
or so instead of default classes?

Are offline players not willing to implement support for the CSS subset  
that applies to WebVTT?

>> The WebVTT rendering rules don't really work like "divs" at all.
>> The rendering rules do things like avoid overlapping. What happens if a
>> rollup cue and a positioned cue within a region overlap?
> The browser should just let that happen it's the responsibility of the
> author to deal with that. If they intended them to overlap, then so be
> it.

I'd rather not support line:n% positioning than not supporting  
avoid-overlapping. If overlapping is possible, it will happen and that's  
bad user experience.

Simon Pieters
Opera Software
Received on Friday, 21 September 2012 06:48:26 UTC

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