Implementing time-based transitions on WebVTT with CSS

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

Received on Monday, 20 August 2012 21:00:00 UTC