Re: Roll-up captions in WebVTT

This is not quite true if the text is duplicated in the WebVTT file.
This would present serious accessibility issues for people who use
screenreaders (and that includes the deaf-blind population). It also
would make searching and indexing harder if text were duplicated.

Christian

On Tue, Nov 29, 2011 at 11:33 AM, David Singer <singer@apple.com> wrote:
> 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.
>
>



-- 
Christian Vogler, PhD
Director, Technology Access Program
Department of Communication Studies
SLCC 1116
Gallaudet University
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VP: 202-250-2795