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.
It would work, at least as a fallback. It seems like we both agree that
semantics should guide style, and not the other way around.
>
> Whether we should have support for arbitrary transformations, the same way
> I rather doubt.
As it's planned currently it doesn't work, yet. Another way to do so
should be thought of, at least for future versions.
>
> 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).
Indeed it is. As of now, it's CSS that adds that transformation layer (a
very smart idea in my opinion). The problem would be to properly map the
captioning layer (WebVTT) in such a way that the styling layer (CSS) is
able to react to the time of the subtitles and do transformations
accordingly. Either that mapping is currently incomplete, or the existing
CSS functions needed to do time-based transitions (if any) have not been
yet considered to interact with WebVTT.
- Carlos Solís

>
> 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 Tuesday, 21 August 2012 00:57:43 UTC