Decoding EIA-608 closed captions in MP4 (created by Final Cut Pro) not working

[fumoboy007]

Summary of the bug

I created an MP4 using Final Cut Pro that contains EIA-608 closed captions. (The closed captions are muxed by Final Cut Pro as a separate stream from the video.) I tried playing this file using ffplay, VLC, and my own video application that uses the FFmpeg libraries; the closed captions are not shown.

More specifically, avcodec_decode_subtitle2 always returns 0 into got_sub_ptr.

How to reproduce

Download the attached sample file and then run the following command:

% ffplay FFmpeg\ EIA-608\ Bug.m4v 
ffplay version 4.1 Copyright (c) 2003-2018 the FFmpeg developers
  built with Apple LLVM version 10.0.0 (clang-1000.11.45.5)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/4.1_1 --enable-shared --enable-pthreads --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gpl --enable-libmp3lame --enable-libopus --enable-libsnappy --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libxvid --enable-lzma --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-librtmp --enable-libspeex --enable-videotoolbox
  libavutil      56. 22.100 / 56. 22.100
  libavcodec     58. 35.100 / 58. 35.100
  libavformat    58. 20.100 / 58. 20.100
  libavdevice    58.  5.100 / 58.  5.100
  libavfilter     7. 40.101 /  7. 40.101
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  3.100 /  5.  3.100
  libswresample   3.  3.100 /  3.  3.100
  libpostproc    55.  3.100 / 55.  3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'FFmpeg EIA-608 Bug.m4v':
  Metadata:
    major_brand     : M4V 
    minor_version   : 1
    compatible_brands: M4V M4A mp42isom
    creation_time   : 2019-01-23T06:04:07.000000Z
  Duration: 00:00:09.44, start: 0.000000, bitrate: 4165 kb/s
    Stream #0:0(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 124 kb/s (default)
    Metadata:
      creation_time   : 2019-01-23T06:04:07.000000Z
      handler_name    : Core Media Audio
    Stream #0:1(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, bt709, progressive), 960x540 [SAR 1:1 DAR 16:9], 4034 kb/s, 25 fps, 25 tbr, 25 tbn, 50 tbc (default)
    Metadata:
      creation_time   : 2019-01-23T06:04:07.000000Z
      handler_name    : Core Media Video
    Stream #0:2(eng): Subtitle: eia_608 (c608 / 0x38303663), 960x540, 0 kb/s (default)
    Metadata:
      creation_time   : 2019-01-23T06:04:07.000000Z
      handler_name    : Core Media Closed Caption

I have also attached an SCC file (generated by Final Cut Pro) that contains only the closed captions.

[fumoboy007]

(I had to cut the video to meet the attachment size requirement, so the duration in the “How to reproduce” section will be slightly different.)

[fumoboy007]

I forgot to mention that QuickTime Player is able to display the closed captions. (I am using macOS 10.14.2.)

[Carl Eugen Hoyos]

This is a duplicate of ticket #4616, thank you for the additional sample!