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RE: Change proposals for issue-152

From: Sean Hayes <Sean.Hayes@microsoft.com>
Date: Tue, 22 Mar 2011 17:33:41 +0000
To: Ian Hickson <ian@hixie.ch>
CC: Philip Jägenstedt <philipj@opera.com>, "public-html@w3.org" <public-html@w3.org>
Message-ID: <8DEFC0D8B72E054E97DC307774FE4B913FAF7481@DB3EX14MBXC313.europe.corp.microsoft.com>
Well I don't agree that the "whole point of having multiple text tracks is that 
the user agent can intelligently avoid overlapping cues while ensuring 
that a single cue doesn't move around when other cues are added or 
removed at the same time" is true, in fact I'm not sure I even understand what you mean by that; why is there a need to fix a caption once placed? 

If you are saying that captions are going to be selected in and fixed in space in temporal order; that makes no sense, as you will end up with different streams interleaved. it's actually far more likely you would want to assign each caption output a fixed distinct region, since the 80% use case for multiple simultaneous cue tracks is mixed language subtitling like Bollywood where they subtitle in both Urdu and Hindi, one individual reader is only going to be looking at one of the streams so they want to always flick eye-gaze directly to where those captions are going to appear.

Allowing multiple caption files to intelligently share a given space is however perfectly possible (see below); I'd much rather that than a bunch of hacked up special case layout rules. If you have identified a layout strategy that CSS can't do, then put it in CSS where it belongs so everyone can share.

<!-- example where cap1,2,3 change their intrinsic height as captions fill them up, and so flow into the containing div; however their relative order is preserved -->
<!DOCTYPE html />
<html>
<head>
    <title>Untitled Page</title>
    <style>
        #captionIntelligence
        {
            position: absolute;
            bottom: 3px;
            width: 400px;
            background: transparent;
            border: solid 1px red;
            color: White;
        }
        #VideoGroup
        {
            background: black;
            position: absolute;
            top: 10px;
            left: 10px;
            width: 400px;
            height: 300px;
        }
        *[kind='captions']
        {
            display: block;
            text-align: center;
            color: White;
        }
    </style>
</head>
<body>
    <div id='VideoGroup'>
        <video id='vid' src='...' >
        </video>
        <div id='captionIntelligence'>
            <cues id='cap1' kind="captions" src='...' ></cues>
            <cues id='cap2' kind="captions" src='...' ></cues>
            <cues id='cap3' kind="captions" src='...' ></cues>
        </div>
    </div>
</body>
</html>

-----Original Message-----
From: Ian Hickson [mailto:ian@hixie.ch] 
Sent: 22 March 2011 15:44
To: Sean Hayes
Cc: Philip Jägenstedt; public-html@w3.org
Subject: RE: Change proposals for issue-152

On Tue, 22 Mar 2011, Sean Hayes wrote:
> 
> To enable multiple <cues> is the same as enabling multiple <videos>, and 
> positioning them is the same as positioning <video>, <audio> or even 
> <div>; you can have as many as you want, it's all just CSS. Silvia and 
> Eric worked out the attributes to select between tracks and to enable 
> them; which works essentially the same as a radio group in a form. This 
> works based on the name and kind attributes.

That doesn't work. The whole point of having multiple text tracks is that 
the user agent can intelligently avoid overlapping cues while ensuring 
that a single cue doesn't move around when other cues are added or 
removed at the same time. CSS can't do that.

-- 
Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'
Received on Tuesday, 22 March 2011 17:34:29 UTC

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