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Overlapping cues and rendering behavior

From: Cyril Concolato <cyril.concolato@telecom-paristech.fr>
Date: Wed, 26 Sep 2012 17:41:09 +0200
Message-ID: <50632215.9020001@telecom-paristech.fr>
To: "public-texttracks@w3.org" <public-texttracks@w3.org>
Hi again,

I've made a small test and the rendering in Opera and Chrome is 
different. I don't know which one is correct.
http://perso.telecom-paristech.fr/~concolat/html5_tests/webvtt-overlapping.html 
<http://perso.telecom-paristech.fr/%7Econcolat/html5_tests/webvtt-overlapping.html>

In Chrome, when 2 cues are active at the same time, and the first one 
becomes inactive, the second one is shifted down by one line. The next 
active cue (the third one) will be displayed on the line above the 
second cue.
In Opera, the remaining active cue is not shifted, it does not move. The 
next active cue (third cue) will take the empty space below the active 
cue. This leads to strange results.
In the above test, this is visible at time 16. Opera displays cue 6, 4, 
5 (from bottom line to top) while Chrome displays 4, 5, 6 (bottom to top).

I tend to prefer Chrome's behavior as this gives the same result if you 
split the overlapping cues so that they do not overlap (see my post for 
more details 
http://concolato.wp.mines-telecom.fr/2012/09/12/webvtt-streaming/).

Comments?

Cyril

-- 
Cyril Concolato
Maître de Conférences/Associate Professor
Groupe Multimedia/Multimedia Group
Telecom ParisTech
46 rue Barrault
75 013 Paris, France
http://concolato.wp.mines-telecom.fr/
Received on Wednesday, 26 September 2012 15:41:40 UTC

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