Re: Roll-up captions in WebVTT

On Feb 27, 2012, at 19:47 , Glenn Maynard wrote:

> On Mon, Feb 27, 2012 at 1:36 PM, David Singer <singer@apple.com> wrote:
> > I don't find explicitly grouping cues together objectionable.  What I don't like is the idea of markup that says "these cues should be rendered as roll-up captions".
> 
> we might be all in agreement here.  I want the VTT language to tell me what text is on screen, and where it goes, and something else (I suggest CSS transitions) to handle smoothness of motion
> 
> It's not immediately obvious to me how transitioning the position would interact with the "Adjust the positions of boxes..." positioning algorithm.
> 
> It may be useful for use cases like scrolling credits and captions that follow signs across the screen (though I wouldn't prioritize it until implementations catch up somewhat).
> 
> I think it would be a bad idea to recommend using transitions to implement roll-up captions by hand, though, if you're suggesting that.  That seems brittle, since it would depend on the exact positioning chosen by the positioning and layout algorithms (to know when and how far things have to move), and it would make it hard for users to toggle roll-ups off if they don't want them.  I think if enough users really want roll-ups, UAs should simply be allowed to switch rendering modes as a user preference, with no change to markup.  (I'm still doubtful that people really want that, though, and I don't know if there would be any unwanted side-effects from permitting UAs that level of rendering freedom.)


I am simply saying that the choice between jump-scroll and smooth-scroll is a presentational one, and not semantic; the text ends up in the same place in either case.  Given that, it seems it should be under control of the (a) presentational system and (b) the user and chosen user-agent.

CSS seems the obvious place to look for that presentational expression since that is, in some sense, CSS's job, and it has a tool - transitions, which are indeed optional.

David Singer
Multimedia and Software Standards, Apple Inc.