theora dev - Apr 2011 - using Kate for WebVTT encapsulation

(sending this publicly so the discussion about this is in the open)

Hi OggK, all,

OggK, you've probably seen that the bug in Firefox for adding Kate
support has been closed as WONTFIX:
https://bugzilla.mozilla.org/show_bug.cgi?id=481529

I've just posted a reply there mentioning how I envisage in-band
WebVTT support to be provided through Kate. I want to ask your
opinion.

In case you haven't heard about WebVTT yet, it's the time-aligned text
format that has been developed by the WHATWG as the baseline text
format for HTML5 media elements, see
http://www.whatwg.org/specs/web-apps/current-work/webvtt.html .
Also see
http://www.whatwg.org/specs/web-apps/current-work/multipage/video.html#the-track-element
for how to include it with a audio or video element.

My idea is that - because WebVTT is so similar to SRT - it would be
simple to support WebVTT in Ogg by encapsulating it in a Kate track
and making sure that it can be extracted again without loss of
information through the kate libraries.

There would only be a few changes necessary:
* WebVTT has a header which needs to be parsed and re-created.
* Also, there is a suggestion for inclusion of name-value Metadata at
the top right after the header, which we'd want to retain (maybe in a
header or a first packet).
* Then there are cue settings, which are position modifiers on each
cue (segment of timed text). They need to be recreated, too.

The marked-up text inside cues needs to be retrieved unchanged.

For an old, but still mostly correct explanation with examples of some
of the things see:
http://annodex.net/~silvia/tmp/WebSRT/ (WebSRT got renamed to WebVTT)
and for something a bit newer see:
http://www.html5videoguide.net/presentations/WebVTT/

I'm just wondering what you think about this kind of approach.

Cheers,
Silvia.

Hi,

sorry for the delay, I haven't been checking mail for a few days.
> My idea is that - because WebVTT is so similar to SRT - it would be
> simple to support WebVTT in Ogg by encapsulating it in a Kate track
> and making sure that it can be extracted again without loss of
> information through the kate libraries.
This would seem easily doable.
However, since WebVTT seems to define all layout/styling, it seems like
shoehorning it, and adding baggage that will be left unused. It is easy to
ignore the decoding of the Kate styling information though, as timing and
text were placed first to allow for simple text only decoders to work like this.
The category present in the header is also meant for decoders to know the
type/purpose of the stream, which would allow a player to know whether a
track is a WebVTT track or not.
> There would only be a few changes necessary:
> * WebVTT has a header which needs to be parsed and re-created.
While I haven't looked at it, it doesn't sound much different from, say,
LRC, which kateenc/katedec can import/export.
> * Also, there is a suggestion for inclusion of name-value Metadata at
> the top right after the header, which we'd want to retain (maybe in a
> header or a first packet).
The second header packets is a Vorbiscomment packet, which is used
for the same thing.
> * Then there are cue settings, which are position modifiers on each
> cue (segment of timed text). They need to be recreated, too.
>
> The marked-up text inside cues needs to be retrieved unchanged.
I don't know what these are, so I can't say offhand whether it would
match.
I'll have a look at those in the URL you quoted.

Hi All,

On 12/04/2011 12:44 p.m., Silvia Pfeiffer wrote:
> OggK, you've probably seen that the bug in Firefox for adding Kate
> support has been closed as WONTFIX:
> https://bugzilla.mozilla.org/show_bug.cgi?id=481529
>
> I've just posted a reply there mentioning how I envisage in-band
> WebVTT support to be provided through Kate. I want to ask your
> opinion.
>
 From our point of view, once we've implemented out-of-band WebVTT 
support, authors will have subtitle support, and so any additional 
in-band subtitle track in Ogg would be redundant.

If we supported WebVTT in Kate (or some other in-band Ogg track) we'd 
increase our maintenance burden. Whereas if we only implement WebVTT 
support inside a <track> element, we can share that implementation 
between WebM and Ogg.

Regards,
Chris P.