Unable to remux AV1 stream from MKV to MKV

[mysterious]

Summary of the bug:

With some MKV source files, copying the AV1 video stream to an MKV output results in effectively no video data in the output file.

How to reproduce:

Run the following command with the attached sample.mkv:

ffmpeg -i sample.mkv -vcodec copy output.mkv

Tested on ffmpeg 6.0.
Output:

ffmpeg version 6.0-full_build-www.gyan.dev Copyright (c) 2000-2023 the FFmpeg developers
  built with gcc 12.2.0 (Rev10, Built by MSYS2 project)
  configuration: --enable-gpl --enable-version3 --enable-static --disable-w32threads --disable-autodetect --enable-fontconfig --enable-iconv --enable-gnutls --enable-libxml2 --enable-gmp --enable-bzlib --enable-lzma --enable-libsnappy --enable-zlib --enable-librist --enable-libsrt --enable-libssh --enable-libzmq --enable-avisynth --enable-libbluray --enable-libcaca --enable-sdl2 --enable-libaribb24 --enable-libdav1d --enable-libdavs2 --enable-libuavs3d --enable-libzvbi --enable-librav1e --enable-libsvtav1 --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs2 --enable-libxvid --enable-libaom --enable-libjxl --enable-libopenjpeg --enable-libvpx --enable-mediafoundation --enable-libass --enable-frei0r --enable-libfreetype --enable-libfribidi --enable-liblensfun --enable-libvidstab --enable-libvmaf --enable-libzimg --enable-amf --enable-cuda-llvm --enable-cuvid --enable-ffnvcodec --enable-nvdec --enable-nvenc --enable-d3d11va --enable-dxva2 --enable-libmfx --enable-libshaderc --enable-vulkan --enable-libplacebo --enable-opencl --enable-libcdio --enable-libgme --enable-libmodplug --enable-libopenmpt --enable-libopencore-amrwb --enable-libmp3lame --enable-libshine --enable-libtheora --enable-libtwolame --enable-libvo-amrwbenc --enable-libilbc --enable-libgsm --enable-libopencore-amrnb --enable-libopus --enable-libspeex --enable-libvorbis --enable-ladspa --enable-libbs2b --enable-libflite --enable-libmysofa --enable-librubberband --enable-libsoxr --enable-chromaprint
  libavutil      58.  2.100 / 58.  2.100
  libavcodec     60.  3.100 / 60.  3.100
  libavformat    60.  3.100 / 60.  3.100
  libavdevice    60.  1.100 / 60.  1.100
  libavfilter     9.  3.100 /  9.  3.100
  libswscale      7.  1.100 /  7.  1.100
  libswresample   4. 10.100 /  4. 10.100
  libpostproc    57.  1.100 / 57.  1.100
[libdav1d @ 000001ba258d8600] libdav1d 1.1.0-3-g98b0c96
Input #0, matroska,webm, from 'sample.mkv':
  Metadata:
    encoder         : libebml v1.4.4 + libmatroska v1.7.1
    creation_time   : 2023-07-08T07:38:01.000000Z
  Duration: 00:00:06.59, start: 0.000000, bitrate: 349 kb/s
  Stream #0:0: Video: av1 (Main), yuv420p10le(tv), 1920x1080, Film Grain, SAR 1:1 DAR 16:9, 23.98 fps, 23.98 tbr, 1k tbn (default)
    Metadata:
      BPS             : 340844
      DURATION        : 00:00:06.590000000
      NUMBER_OF_FRAMES: 158
      NUMBER_OF_BYTES : 280771
      _STATISTICS_WRITING_APP: mkvmerge v77.0 ('Elemental') 64-bit
      _STATISTICS_WRITING_DATE_UTC: 2023-07-08 07:38:01
      _STATISTICS_TAGS: BPS DURATION NUMBER_OF_FRAMES NUMBER_OF_BYTES
Output #0, matroska, to 'out.mkv':
  Metadata:
    encoder         : Lavf60.3.100
  Stream #0:0: Video: av1 (Main) (AV01 / 0x31305641), yuv420p10le(tv), 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 23.98 fps, 23.98 tbr, 1k tbn (default)
    Metadata:
      BPS             : 340844
      DURATION        : 00:00:06.590000000
      NUMBER_OF_FRAMES: 158
      NUMBER_OF_BYTES : 280771
      _STATISTICS_WRITING_APP: mkvmerge v77.0 ('Elemental') 64-bit
      _STATISTICS_WRITING_DATE_UTC: 2023-07-08 07:38:01
      _STATISTICS_TAGS: BPS DURATION NUMBER_OF_FRAMES NUMBER_OF_BYTES
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
Press [q] to stop, [?] for help
frame=    0 fps=0.0 q=-1.0 Lsize=       1kB time=-577014:32:22.77 bitrate=N/A speed=N/A    d=N/A
video:0kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown

Note the "video:0kB" output.

Adding -v debug causes a bunch of "cur_dts is invalid" errors to be spat out, if that matters.

[mkver]

The parser does not see any keyframes in your input (although the first packet is marked as keyframe in your input sample on the container level); because all input before the first keyframe is discarded by default, all input is discarded.

The sample in question contains a frame header indicating a key frame followed by a Tile Group containing a frame header indicating an inter frame. Because of the latter, the parser flags the packet as non-keyframe.

You can use -copyinkf (output option) or -fflags +noparse (input option) as a workaround.

[mysterious]

Thanks so much for the info and suggestions!