W3C home > Mailing lists > Public > public-texttracks@w3.org > November 2011

Re: Roll-up captions in WebVTT

From: David Singer <singer@apple.com>
Date: Tue, 29 Nov 2011 17:33:30 +0100
Message-id: <FD47FFA9-1B45-4D55-9108-83EE357D3CB6@apple.com>
To: public-texttracks@w3.org
I think a fundamental question that needs addressing is whether we expect roll-up to be (a) 'part of' the core VTT vocabulary or (b) a presentational issue that is 'optional'?

I tend to think the latter.  Yes, maybe smooth roll-up is easier on the eye than jump-scroll, but the same information is presented.

If that is the case, I think using CSS transitions is a good candidate.  Alas, we don't use CSS positioning (for obvious reasons -- positioning DOES have to be part of the core of VTT).  But that doesn't hose us.

Consider a stream that has Line1, Line2, . LineN, showing in a three-line area.  A simple way to jump scroll that is simply to repeat each line, every time it 'moves' in the 3-line display.

<blank>
<blank>
Line1

then

<blank>
Line1
Line2

Line1
Line2
Line3

Line2
Line3
Line4

displayed simply, the lines appear to jump.

If we can convince the CSS engine that Line1 in the first cue is the same as Line1 in the second, we could ask for a transition on, say, 'y'.  That's pretty easy to do with markup -- if a line of text in two consecutive cues has the same marked-id, then it's the same, and any CS transitions declared on its class apply, if you use CSS.

Saying CSS transitions can be used to smooth out display transitions also allows for fade-in/fade-out (transition on color), and so on.


David Singer
Multimedia and Software Standards, Apple Inc.
Received on Tuesday, 29 November 2011 16:34:01 UTC

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