-c:v libtheora is broken since 4.1

[johnkdelaney1963]

Summary of the bug:
"-c:v libtheora" ruins the video output (garbled, dropped frames, etc.) on my end with ffmpeg 4.1.0 or newer. No issue with 4.0.2 or older.

How to reproduce:
Encode any video file to .ogv container with "-c:v libtheora" codec option using ffmpeg 4.1.0 or newer.

[Carl Eugen Hoyos]

$ ffmpeg -i Vertical400kbit.sorenson3.mov out.ogv      
ffmpeg version N-96374-gb55c6b8c40 Copyright (c) 2000-2020 the FFmpeg developers
  built with gcc 9 (SUSE Linux)
  configuration: --enable-gpl --enable-libtheora --enable-libvorbis
  libavutil      56. 38.100 / 56. 38.100
  libavcodec     58. 65.103 / 58. 65.103
  libavformat    58. 35.102 / 58. 35.102
  libavdevice    58.  9.103 / 58.  9.103
  libavfilter     7. 71.100 /  7. 71.100
  libswscale      5.  6.100 /  5.  6.100
  libswresample   3.  6.100 /  3.  6.100
  libpostproc    55.  6.100 / 55.  6.100
Guessed Channel Layout for Input Stream #0.1 : mono
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'Vertical400kbit.sorenson3.mov':
  Metadata:
    creation_time   : 2001-03-20T16:17:18.000000Z
    title           : Vertical Online SV3 Demo
    title-eng       : Vertical Online SV3 Demo
    artist          : Logan Kelsey
    artist-eng      : Logan Kelsey
    copyright       : © Vertical Online 2001
    copyright-eng   : © Vertical Online 2001
    encoder         : Sorenson Video 3
    encoder-eng     : Sorenson Video 3
  Duration: 00:00:43.58, start: 0.000000, bitrate: 580 kb/s
    Stream #0:0(eng): Video: svq3 (SVQ3 / 0x33515653), yuvj420p(pc), 320x240, 391 kb/s, 30.02 fps, 30 tbr, 600 tbn, 600 tbc (default)
    Metadata:
      creation_time   : 2001-03-20T16:17:18.000000Z
      handler_name    : Apple Video Media Handler
      encoder         : Sorenson Video 3
    Stream #0:1(eng): Audio: adpcm_ima_qt (ima4 / 0x34616D69), 44100 Hz, mono, s16p, 176 kb/s (default)
    Metadata:
      creation_time   : 2001-03-20T16:17:18.000000Z
      handler_name    : Apple Sound Media Handler
Stream mapping:
  Stream #0:0 -> #0:0 (svq3 (native) -> theora (libtheora))
  Stream #0:1 -> #0:1 (adpcm_ima_qt (native) -> vorbis (libvorbis))
Press [q] to stop, [?] for help
[adpcm_ima_qt] Multiple frames in a packet.
[swscaler] deprecated pixel format used, make sure you did set range correctly
Output #0, ogv, to 'out.ogv':
  Metadata:
    encoder         : Lavf58.35.102
    title           : Vertical Online SV3 Demo
    title-eng       : Vertical Online SV3 Demo
    artist          : Logan Kelsey
    artist-eng      : Logan Kelsey
    copyright       : © Vertical Online 2001
    copyright-eng   : © Vertical Online 2001
    Stream #0:0(eng): Video: theora (libtheora), yuv420p, 320x240, q=2-31, 200 kb/s, 30 fps, 30 tbn, 30 tbc (default)
    Metadata:
      creation_time   : 2001-03-20T16:17:18.000000Z
      handler_name    : Apple Video Media Handler
      encoder         : Lavc58.65.103 libtheora
      title           : Vertical Online SV3 Demo
      title-eng       : Vertical Online SV3 Demo
      artist          : Logan Kelsey
      artist-eng      : Logan Kelsey
      copyright       : © Vertical Online 2001
      copyright-eng   : © Vertical Online 2001
    Stream #0:1(eng): Audio: vorbis (libvorbis), 44100 Hz, mono, fltp (default)
    Metadata:
      creation_time   : 2001-03-20T16:17:18.000000Z
      handler_name    : Apple Sound Media Handler
      encoder         : Lavc58.65.103 libvorbis
      title           : Vertical Online SV3 Demo
      title-eng       : Vertical Online SV3 Demo
      artist          : Logan Kelsey
      artist-eng      : Logan Kelsey
      copyright       : © Vertical Online 2001
      copyright-eng   : © Vertical Online 2001
frame= 1308 fps=289 q=-0.0 Lsize=    1466kB time=00:00:43.60 bitrate= 275.5kbits/s speed=9.62x    
video:1058kB audio:385kB subtitle:0kB other streams:0kB global headers:6kB muxing overhead: 1.545271%

[johnkdelaney1963]

working 4.0.2 encode

[johnkdelaney1963]

broken 20200113-7225479 encode

[johnkdelaney1963]

Please try the input.mp4 attachment with the below commands and see if you get a similar broken encode.

ffmpeg -i input.mp4 -c:v libtheora -b:v 1.7M -an output.ogv