[FFmpeg-trac] #5434(undetermined:new): add support of WebVTT subtitles in Matroksa files

[FFmpeg]

#5434: add support of WebVTT subtitles in Matroksa files
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             Reporter:  Klaus1189    |                     Type:
               Status:  new          |  enhancement
            Component:               |                 Priority:  normal
  undetermined                       |                  Version:
             Keywords:               |  unspecified
             Blocking:               |               Blocked By:
Analyzed by developer:  0            |  Reproduced by developer:  0
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 I contacted Moritz Bunkus, the developer of MKVToolNix, because according
 to ironic_monkey from Kodi forum FFMPEG doesn't support the new spec. Here
 you can see the full thread at Kodi forum:
 http://forum.kodi.tv/showthread.php?tid=261529&pid=2309291

 Moritz Bunkus explained the issue to me.
 Up until a couple of days ago the storage of WebVTT in Matroska hadn't
 been specified yet. What ffmpeg seems to support (D_WEBVTT/…) is an old
 and outdated work-in-progress paper by the WebM project[1]. We (as in the
 Matroska project) have decided not to use their proposal in Matroska
 for several reasons:

 1. The proposal is old (from February 2012). The WebVTT specs have changed
 considerably since then, and therefore the WebM proposal doesn't handle
 several of those additions and changes.

 2. It suggests splitting the single WebVTT file into multiple tracks
 inside WebM. This is possible but it makes handling of multiple tracks
 more difficult than it has to be for demuxers and remuxers. Additionally
 there's no way to specify that several tracks belong to the same logical
 track and must be handled all at once.

 3. The WebM proposal is still a work in progress and WebM still officially
 doesn't support subtitles at all[2].

 The Matroska project has now formalized the storage of WebVTT in
 Matroska[3]. The specs have been added to the Matroska web site[4].

 The next step should be to add support in ffmpeg for the current storage
 method.

 [1]  http://wiki.webmproject.org/webm-metadata/temporal-metadata/webvtt-
 in-webm
 [2]  http://www.webmproject.org/docs/container/
 [3]  http://thread.gmane.org/gmane.comp.multimedia.matroska.devel/5210
 [4]  https://www.matroska.org/technical/specs/subtitles/webvtt.html


 Here you can get a sample file:
 https://drive.google.com/file/d/0B4y5u0gBKYqbSFczT1VPc2l5SXM/view?usp=sharing

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Ticket URL: <https://trac.ffmpeg.org/ticket/5434>
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