dvdsub with dimensions cannot be transcoded

[Aman]

Input dvdsub subtitle tracks that have widthxheight dimensions cannot be converted because the output encoder rejects the height/width codec parameters:

$ ffmpeg -i sample.mkv -c:v none -c:a none -map 0:2 out.srt
ffmpeg version 2.2.git Copyright (c) 2000-2014 the FFmpeg developers
  built on May  9 2014 21:42:55 with Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/HEAD --enable-shared --enable-pthreads --enable-gpl --enable-version3 --enable-nonfree --enable-hardcoded-tables --enable-avresample --enable-vda --cc=clang --host-cflags= --host-ldflags= --enable-libx264 --enable-libfaac --enable-libmp3lame --enable-libxvid
  libavutil      52. 81.100 / 52. 81.100
  libavcodec     55. 60.103 / 55. 60.103
  libavformat    55. 37.102 / 55. 37.102
  libavdevice    55. 13.101 / 55. 13.101
  libavfilter     4.  5.100 /  4.  5.100
  libavresample   1.  2.  0 /  1.  2.  0
  libswscale      2.  6.100 /  2.  6.100
  libswresample   0. 18.100 /  0. 18.100
  libpostproc    52.  3.100 / 52.  3.100
Input #0, matroska,webm, from 'sample.mkv':
  Metadata:
    encoder         : libebml v1.2.3 + libmatroska v1.3.0
    creation_time   : 2012-05-14 10:51:44
  Duration: 02:16:17.96, start: 0.000000, bitrate: 0 kb/s
    Stream #0:0(eng): Video: h264 (High), yuv420p(tv, bt709), 1440x600 [SAR 1:1 DAR 12:5], 23.98 fps, 23.98 tbr, 1k tbn, 47.95 tbc (default)
    Metadata:
      title           : @5363Kbps High Profiles @L4.1
    Stream #0:1(eng): Audio: dts (DTS), 48000 Hz, 5.1(side), fltp, 1536 kb/s (default)
    Metadata:
      title           : DTS@1536Kbps 6 chnls
    Stream #0:2(eng): Subtitle: dvd_subtitle, 1280x720 (default)
    Stream #0:3(tur): Subtitle: dvd_subtitle, 1280x720
    Stream #0:4(ara): Subtitle: dvd_subtitle, 1280x720
    Stream #0:5(bul): Subtitle: dvd_subtitle, 1280x720
    Stream #0:6(chi): Subtitle: dvd_subtitle, 1280x720
    Stream #0:7(hrv): Subtitle: dvd_subtitle, 1280x720
    Stream #0:8(cze): Subtitle: dvd_subtitle, 1280x720
    Stream #0:9(dan): Subtitle: dvd_subtitle, 1280x720
    Stream #0:10(dut): Subtitle: dvd_subtitle, 1280x720
    Stream #0:11(fin): Subtitle: dvd_subtitle, 1280x720
    Stream #0:12(fre): Subtitle: dvd_subtitle, 1280x720
    Stream #0:13(ger): Subtitle: dvd_subtitle, 1280x720
    Stream #0:14(heb): Subtitle: dvd_subtitle, 1280x720
    Stream #0:15(hun): Subtitle: dvd_subtitle, 1280x720
    Stream #0:16(ind): Subtitle: dvd_subtitle, 1280x720
    Stream #0:17(ita): Subtitle: dvd_subtitle, 1280x720
    Stream #0:18(jpn): Subtitle: dvd_subtitle, 1280x720
    Stream #0:19(kor): Subtitle: dvd_subtitle, 1280x720
    Stream #0:20(pol): Subtitle: dvd_subtitle, 1280x720
    Stream #0:21(por): Subtitle: dvd_subtitle, 1280x720
    Stream #0:22(rum): Subtitle: dvd_subtitle, 1280x720
    Stream #0:23(rus): Subtitle: dvd_subtitle, 1280x720
    Stream #0:24(srp): Subtitle: dvd_subtitle, 1280x720
    Stream #0:25(spa): Subtitle: dvd_subtitle, 1280x720
    Stream #0:26(swe): Subtitle: dvd_subtitle, 1280x720
    Stream #0:27(tha): Subtitle: dvd_subtitle, 1280x720
Output #0, srt, to 'out.srt':
  Metadata:
    encoder         : libebml v1.2.3 + libmatroska v1.3.0
    Stream #0:0(eng): Subtitle: subrip, 1280x720 (default)
Stream mapping:
  Stream #0:2 -> #0:0 (dvdsub -> subrip)
Error while opening encoder for output stream #0:0 - maybe incorrect parameters such as bit_rate, rate, width or height

[Cigaes]

You missed maybe when reading the error message.

The actual issue is much simpler: dvdsub is made of images, subrip is made of text. If you built ffmpeg with support for OCR, please share your patch. Otherwise, no chance that will work.

[Aman]

Ah, well, that would explain it. Thanks.