Support for advanced caption features (inc rollup)

 Hi all,

As part of an effort to substantially support all CEA-608 and CEA-708
features in VTT we (at YouTube/Google) have gone ahead with the previously
discussed suggestion of a "Region" [1].

We have update the proposed specification of the "Region:" setting at
http://www.w3.org/community/texttracks/wiki/MultiCueBox .

Some of the features that this proposed cue setting allows are:
* It allows to handle a group of captions together, e.g. middle align them
together within a box, move them together to a different screen location.
* It allows advanced styling of CEA-708, e.g. have a different background
box color to the background color of the caption text, while having a
dynamically sized region based on the number of cues in it.
* It allows doing roll-up or roll-down of captions within a region, since
it specifies the number of visible lines, and the rolling direction. This
includes a transition effect.

We have implemented a demonstration of "Region" in JavaScript.
You can see the regions in action with roll-up captions and a different
background text color at
http://html5videoguide.net/test/WebVTT-with-regions/cpc_video.html from
about 50 sec.
 The source for this is available at
https://github.com/silviapfeiffer/WebVTT-with-regions . [2]

We have also included the "Region" feature in the Conversion specification
for CEA-608 and CEA-708 captions:
http://dvcs.w3.org/hg/text-tracks/raw-file/default/608toVTT/608toVTT.html
It is used to support CEA-608 rollup captions and all of the CEA-708
features, since it maps directly to the CEA-708 concept of "window".

We have further implemented a first rough WebVTT export in YouTube that
includes the "Region" feature and roughly follows the spec (we are still
ironing out some kinks).
An example file is attached which relates to this video:
http://www.youtube.com/watch?v=zEKLqMS_HuA
. <http://www.youtube.com/watch?v=zEKLqMS_HuA>
Video owners are able to download VTT files of their own videos' captions
through the YouTube GData API.

We would like to get feedback from other Browser vendors about the "Region"
feature and whether they would consider implementing it.

Best Regards,
Silvia
(this time as a Google/YouTube representative).


[1] http://lists.w3.org/Archives/Public/public-texttracks/2012Sep/0011.html
[2] Thanks to Anne's WebVTT parser at https://github.com/annevk/webvtt ,
which this code is based on.