[FFmpeg-trac] #5641(avformat:new): Support WebVTT according to MKV specs

14 Jun 2016

      #5641: Support WebVTT according to MKV specs
-------------------------------------+-------------------------------------
             Reporter:  RiCON        |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:  avformat     |                  Version:  git-
             Keywords:  webvtt       |  master
  matroska                           |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 FFmpeg supports the D_WEBVTT/SUBTITLES flavor following WebM specs
 (http://www.webmproject.org/docs/container/), but not the recent
 S_TEXT/WEBVTT flavor added to Matroska spec
 (https://matroska.org/technical/specs/codecid/index.html), likely close to
 it being added to mkvtoolnix in
 https://github.com/mbunkus/mkvtoolnix/commit/c0c8ea01 .

 It should probably also be changed to mux WebVTT tracks as S_TEXT/WEBVTT,
 at least to Matroska so mkvtoolnix recognizes the track as valid
 subtitles.

 {{{
 ffmpeg -i cut-vtt.mkv
 ffmpeg version N-80317-gff53b66-g9da27fb+1 Copyright (c) 2000-2016 the
 FFmpeg developers
   built with gcc 5.4.0 (Rev1, Built by MSYS2 project)
   configuration:  --enable-libx264 --enable-libvpx --enable-libopus
 --disable-postproc --disable-doc --disable-demuxer=asf --disable-ffplay
 --enable-gpl --disable-debug
   libavutil      55. 24.100 / 55. 24.100
   libavcodec     57. 46.100 / 57. 46.100
   libavformat    57. 38.100 / 57. 38.100
   libavdevice    57.  0.101 / 57.  0.101
   libavfilter     6. 46.101 /  6. 46.101
   libswscale      4.  1.100 /  4.  1.100
   libswresample   2.  1.100 /  2.  1.100
 [matroska,webm @ 000000038f2d1c60] Unknown/unsupported AVCodecID
 S_TEXT/WEBVTT.
 [matroska,webm @ 000000038f2d1c60] Could not find codec parameters for
 stream 3 (Subtitle: none): unknown codec
 Consider increasing the value for the 'analyzeduration' and 'probesize'
 options
 Input #0, matroska,webm, from 'cut-vtt.mkv':
   Metadata:
     encoder         : libebml v1.3.3 + libmatroska v1.4.4
     creation_time   : 2016-06-14 12:56:53
   Duration: 00:00:11.28, start: 0.000000, bitrate: 352 kb/s
     Stream #0:0: Video: vp9 (Profile 2), yuv420p10le(tv), 1280x720, SAR
 1:1 DAR 16:9, 23.98 fps, 23.98 tbr, 1k tbn, 1k tbc (default)
     Metadata:
       BPS             : 291322
       BPS-eng         : 291322
       DURATION        : 00:00:09.760000000
       DURATION-eng    : 00:00:09.760000000
       NUMBER_OF_FRAMES: 234
       NUMBER_OF_FRAMES-eng: 234
       NUMBER_OF_BYTES : 355414
       NUMBER_OF_BYTES-eng: 355414
       _STATISTICS_WRITING_APP: mkvmerge v9.2.0 ('Photograph') 64bit
       _STATISTICS_WRITING_APP-eng: mkvmerge v9.2.0 ('Photograph') 64bit
       _STATISTICS_WRITING_DATE_UTC: 2016-06-14 12:56:53
       _STATISTICS_WRITING_DATE_UTC-eng: 2016-06-14 12:56:53
       _STATISTICS_TAGS: BPS DURATION NUMBER_OF_FRAMES NUMBER_OF_BYTES
       _STATISTICS_TAGS-eng: BPS DURATION NUMBER_OF_FRAMES NUMBER_OF_BYTES
     Stream #0:1: Audio: opus, 48000 Hz, stereo, fltp (default) (forced)
     Metadata:
       BPS             : 107013
       BPS-eng         : 107013
       DURATION        : 00:00:09.758000000
       DURATION-eng    : 00:00:09.758000000
       NUMBER_OF_FRAMES: 488
       NUMBER_OF_FRAMES-eng: 488
       NUMBER_OF_BYTES : 130530
       NUMBER_OF_BYTES-eng: 130530
       _STATISTICS_WRITING_APP: mkvmerge v9.2.0 ('Photograph') 64bit
       _STATISTICS_WRITING_APP-eng: mkvmerge v9.2.0 ('Photograph') 64bit
       _STATISTICS_WRITING_DATE_UTC: 2016-06-14 12:56:53
       _STATISTICS_WRITING_DATE_UTC-eng: 2016-06-14 12:56:53
       _STATISTICS_TAGS: BPS DURATION NUMBER_OF_FRAMES NUMBER_OF_BYTES
       _STATISTICS_TAGS-eng: BPS DURATION NUMBER_OF_FRAMES NUMBER_OF_BYTES
     Stream #0:2(eng): Subtitle: webvtt
     Metadata:
       title           : FFmpeg
       BPS             : 163
       BPS-eng         : 163
       DURATION        : 00:00:10.300000000
       DURATION-eng    : 00:00:10.300000000
       NUMBER_OF_FRAMES: 5
       NUMBER_OF_FRAMES-eng: 5
       NUMBER_OF_BYTES : 211
       NUMBER_OF_BYTES-eng: 211
       _STATISTICS_WRITING_APP: mkvmerge v9.2.0 ('Photograph') 64bit
       _STATISTICS_WRITING_APP-eng: mkvmerge v9.2.0 ('Photograph') 64bit
       _STATISTICS_WRITING_DATE_UTC: 2016-06-14 12:56:53
       _STATISTICS_WRITING_DATE_UTC-eng: 2016-06-14 12:56:53
       _STATISTICS_TAGS: BPS DURATION NUMBER_OF_FRAMES NUMBER_OF_BYTES
       _STATISTICS_TAGS-eng: BPS DURATION NUMBER_OF_FRAMES NUMBER_OF_BYTES
     Stream #0:3: Subtitle: none (default)
     Metadata:
       title           : mkvmerge
       BPS             : 0
       BPS-eng         : 0
       DURATION        : 00:00:00.000000000
       DURATION-eng    : 00:00:00.000000000
       NUMBER_OF_FRAMES: 0
       NUMBER_OF_FRAMES-eng: 0
       NUMBER_OF_BYTES : 0
       NUMBER_OF_BYTES-eng: 0
       _STATISTICS_WRITING_APP: mkvmerge v9.2.0 ('Photograph') 64bit
       _STATISTICS_WRITING_APP-eng: mkvmerge v9.2.0 ('Photograph') 64bit
       _STATISTICS_WRITING_DATE_UTC: 2016-06-14 12:56:53
       _STATISTICS_WRITING_DATE_UTC-eng: 2016-06-14 12:56:53
       _STATISTICS_TAGS: BPS DURATION NUMBER_OF_FRAMES NUMBER_OF_BYTES
       _STATISTICS_TAGS-eng: BPS DURATION NUMBER_OF_FRAMES NUMBER_OF_BYTES
 At least one output file must be specified
 }}}

--
Ticket URL: <https://trac.ffmpeg.org/ticket/5641>
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