[FFmpeg-trac] #5056(avcodec:new): Empty cues when converting ASS embedded in MKV to SRT

[FFmpeg]

#5056: Empty cues when converting ASS embedded in MKV to SRT
---------------------------------+--------------------------------------
             Reporter:  eelco    |                     Type:  defect
               Status:  new      |                 Priority:  important
            Component:  avcodec  |                  Version:  git-master
             Keywords:  ass,srt  |               Blocked By:
             Blocking:           |  Reproduced by developer:  0
Analyzed by developer:  0        |
---------------------------------+--------------------------------------
 For some files, extracting ASS subtitles as SRT fails. All timestamps are
 in the output, but the text is empty.

 I’ve tracked this down to the `[Events]` section and `Format:` line not
 being part of the `extradata` / `subtitle_header`. Looking at the specs at
 http://www.matroska.org/technical/specs/subtitles/ssa.html these lines
 don’t have to be part of the CodecPrivate element in an MKV, so I expect
 that’s what’s going on.

 {{{
 % ffmpeg -i sample.mkv -t 150 -f srt pipe:1
 ffmpeg version N-76978-gfb1bf44 Copyright (c) 2000-2015 the FFmpeg
 developers
   built with Apple LLVM version 7.0.0 (clang-700.1.76)
   configuration: --prefix=/Users/eelco/Projects/Beamer/FFmpeg/build
   libavutil      55.  9.100 / 55.  9.100
   libavcodec     57. 16.101 / 57. 16.101
   libavformat    57. 19.100 / 57. 19.100
   libavdevice    57.  0.100 / 57.  0.100
   libavfilter     6. 18.100 /  6. 18.100
   libswscale      4.  0.100 /  4.  0.100
   libswresample   2.  0.101 /  2.  0.101
 Input #0, matroska,webm, from 'sample.mkv':
   Metadata:
     ENCODER         : Lavf57.19.100
   Duration: 00:55:57.79, bitrate: 0 kb/s
     Stream #0:0(eng): Subtitle: ass (default)
     Metadata:
       ENCODER         : Lavc57.16.101 ass
       DURATION        : 00:55:57.790000000
 Output #0, srt, to 'pipe:1':
   Metadata:
     encoder         : Lavf57.19.100
     Stream #0:0(eng): Subtitle: subrip (srt) (default)
     Metadata:
       DURATION        : 00:55:57.790000000
       encoder         : Lavc57.16.101 srt
 Stream mapping:
   Stream #0:0 -> #0:0 (ass (native) -> subrip (srt))
 Press [q] to stop, [?] for help
 1
 00:01:28,948 --> 00:01:30,578


 2
 00:01:31,743 --> 00:01:33,953


 3
 00:02:16,496 --> 00:02:18,536


 4
 00:02:19,499 --> 00:02:21,209


 5
 00:02:22,710 --> 00:02:24,830


 size=       0kB time=00:02:22.71 bitrate=   0.0kbits/s
 video:0kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB
 muxing overhead: unknown
 Output file is empty, nothing was encoded (check -ss / -t / -frames
 parameters if used)
 }}}

--
Ticket URL: <https://trac.ffmpeg.org/ticket/5056>
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