Re: Implementing time-based transitions on WebVTT with CSS

In general, I think we have thought that smooth *transitions* between things that VTT can express, could be expressed in the (optional) presentation  layer by associating CSS transitions with the appropriate classes.  This is 'safe', because in the absence of the appropriate degree of CSS support, one gets abrupt transitions, which is semantically the same.

Whether we should have support for arbitrary transformations, the same way I rather doubt.

I think VTT is intended as a captioning/sub-title layer primarily;  you'll need a ton of extra features if you want to use to make 'real content' that has text in it (smooth blending, transformations, and so on).

On Aug 20, 2012, at 13:59 , "Carlos Solís" <csolisr@riseup.net> wrote:

> 
> Thanks to CSS, WebVTT is able to implement several subtitle effects.
> However, it still doesn't seem to be able to implement time-based
> transitions: for example, movement and rotation of text, fade-ins and
> fade-outs, color transitions, and time-based clipping. All of the above
> are used for typesetting (especially signs) in videos where on-stage texts
> are translated, particularly when those texts move during the video. (An
> example: http://www.youtube.com/watch?v=TxOpkY65Xrk where the text of a
> moving package is translated, and the text moves following the movement of
> said package.) There is a limited way to indicate changes at the start and
> end of karaoke (via the :start and :end CSS tags), but is it possible to
> implement smooth transitions based upon those tags? In a related topic,
> non-browser players (because of safety and coding concerns) require to
> decide upon the subset of CSS that will be allowed to be used by WebVTT.
> 
> - Carlos Solís
> 
> 

David Singer
Multimedia and Software Standards, Apple Inc.

Received on Monday, 20 August 2012 22:55:07 UTC