Behavior of map_metadata -1 no longer strips metadata as expected

[migan10]

Summary of the bug:

Until recently, using "-map_metadata -1" would strip all metadata from an input file, including global and stream metadata (excepting bitstream metadata). Now, using -map_metadata -1 seems to have no effect or may just affect global metadata. I can't figure out the correct method to strip metadata from individual streams, if there is one.

I have run a bisect and the responsible commit is here, from November 2022:
​https://github.com/FFmpeg/FFmpeg/commit/41194806812a31d25e24c535fcb92d7d97b8ce9d

How to reproduce:

Simply try using -map_metadata -1 with any input file that has metadata on any of the streams. May potentially be specific to mkv muxer, as that's all I've tested with. In example below you can see the metadata reappear in the output file details despite setting -map_metadata -1.

% ffmpeg -i in.mkv -map_metadata -1 -map_chapters -1 -c copy -y out.mkv
ffmpeg version N-109647-gba36e6ed52 Copyright (c) 2000-2023 the FFmpeg developers
  built with gcc 12 (Debian 12.2.0-13)
  configuration: --disable-ffplay --disable-doc --prefix=/opt/ffmpeg/build --pkg-config-flags=--static --extra-cflags='-I/opt/ffmpeg/build/include -I/usr/include/samba-4.0 -march=native' --extra-ldflags=-L/opt/ffmpeg/build/lib --extra-libs='-lpthread -lm' --bindir=/opt/ffmpeg/bin --enable-gpl --enable-version3 --enable-libaom --enable-libass --enable-libfdk-aac --enable-libfreetype --enable-libmp3lame --enable-libopus --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-nonfree --enable-libcaca --enable-libaribb24 --enable-libbs2b --enable-libcdio --enable-libcodec2 --enable-libgme --enable-libgsm --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libpulse --enable-librtmp --enable-librubberband --enable-libsnappy --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libwebp --enable-libxvid --enable-lv2 --enable-opencl --enable-libdrm --enable-cuda-nvcc --enable-openssl --enable-ffnvcodec --enable-nvenc --enable-nvdec --enable-libnpp --enable-libzimg --enable-libzvbi --enable-libxml2 --enable-filter=scale_cuda --enable-libvmaf
  libavutil      57. 44.100 / 57. 44.100
  libavcodec     59. 56.100 / 59. 56.100
  libavformat    59. 35.100 / 59. 35.100
  libavdevice    59.  8.101 / 59.  8.101
  libavfilter     8. 54.100 /  8. 54.100
  libswscale      6.  8.112 /  6.  8.112
  libswresample   4.  9.100 /  4.  9.100
  libpostproc    56.  7.100 / 56.  7.100
Input #0, matroska,webm, from 'in.mkv':
  Metadata:
    ENCODER         : Lavf59.35.100
  Duration: 00:25:26.43, start: 0.000000, bitrate: 2743 kb/s
  Chapters:
    Chapter #0:0: start 0.000000, end 739.805733
      Metadata:
        title           : Chapter 01
    Chapter #0:1: start 739.805733, end 1526.424900
      Metadata:
        title           : Chapter 02
  Stream #0:0: Video: hevc (Main 10), yuv420p10le(tv, progressive), 710x480 [SAR 8:9 DAR 71:54], 59.94 fps, 59.94 tbr, 1k tbn
    Metadata:
      ENCODER         : Lavc59.56.100 hevc_nvenc
      DURATION        : 00:25:26.425000000
  Stream #0:1(eng): Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s (default)
    Metadata:
      title           : Stereo
      BPS-eng         : 192000
      DURATION-eng    : 00:25:26.400000000
      NUMBER_OF_FRAMES-eng: 47700
      NUMBER_OF_BYTES-eng: 36633600
      SOURCE_ID-eng   : 0180BD
      _STATISTICS_WRITING_APP-eng: MakeMKV v1.17.2 linux(x64-release)
      _STATISTICS_WRITING_DATE_UTC-eng: 2023-01-27 07:48:22
      _STATISTICS_TAGS-eng: BPS DURATION NUMBER_OF_FRAMES NUMBER_OF_BYTES SOURCE_ID
      DURATION        : 00:25:26.400000000
  Stream #0:2(eng): Subtitle: ass (default)
    Metadata:
      BPS-eng         : 436
      DURATION-eng    : 00:24:56.962000000
      NUMBER_OF_FRAMES-eng: 835
      NUMBER_OF_BYTES-eng: 81624
      SOURCE_ID-eng   : 0100E0
      _STATISTICS_WRITING_APP-eng: MakeMKV v1.17.2 linux(x64-release)
      _STATISTICS_WRITING_DATE_UTC-eng: 2023-01-27 07:48:22
      _STATISTICS_TAGS-eng: BPS DURATION NUMBER_OF_FRAMES NUMBER_OF_BYTES SOURCE_ID
      ENCODER         : Lavc59.56.100 ssa
      DURATION        : 00:24:58.596000000
Output #0, matroska, to 'out.mkv':
  Metadata:
    encoder         : Lavf59.35.100
  Stream #0:0: Video: hevc (Main 10), yuv420p10le(tv, progressive), 710x480 [SAR 8:9 DAR 71:54], q=2-31, 59.94 fps, 59.94 tbr, 1k tbn
    Metadata:
      ENCODER         : Lavc59.56.100 hevc_nvenc
      DURATION        : 00:25:26.425000000
  Stream #0:1(eng): Audio: ac3 ([0] [0][0] / 0x2000), 48000 Hz, stereo, fltp, 192 kb/s (default)
    Metadata:
      title           : Stereo
      BPS-eng         : 192000
      DURATION-eng    : 00:25:26.400000000
      NUMBER_OF_FRAMES-eng: 47700
      NUMBER_OF_BYTES-eng: 36633600
      SOURCE_ID-eng   : 0180BD
      _STATISTICS_WRITING_APP-eng: MakeMKV v1.17.2 linux(x64-release)
      _STATISTICS_WRITING_DATE_UTC-eng: 2023-01-27 07:48:22
      _STATISTICS_TAGS-eng: BPS DURATION NUMBER_OF_FRAMES NUMBER_OF_BYTES SOURCE_ID
      DURATION        : 00:25:26.400000000
  Stream #0:2(eng): Subtitle: ass (default)
    Metadata:
      BPS-eng         : 436
      DURATION-eng    : 00:24:56.962000000
      NUMBER_OF_FRAMES-eng: 835
      NUMBER_OF_BYTES-eng: 81624
      SOURCE_ID-eng   : 0100E0
      _STATISTICS_WRITING_APP-eng: MakeMKV v1.17.2 linux(x64-release)
      _STATISTICS_WRITING_DATE_UTC-eng: 2023-01-27 07:48:22
      _STATISTICS_TAGS-eng: BPS DURATION NUMBER_OF_FRAMES NUMBER_OF_BYTES SOURCE_ID
      ENCODER         : Lavc59.56.100 ssa
      DURATION        : 00:24:58.596000000
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #0:1 -> #0:1 (copy)
  Stream #0:2 -> #0:2 (copy)
Press [q] to stop, [?] for help
frame=54550 fps=36267 q=-1.0 size=  298240kB time=00:15:10.02 bitrate=2684.7kbits/s speed= 605x  

Patches should be submitted to the ffmpeg-devel mailing list and not this bug tracker.

[migan10]

It looks like you can approximate the same behavior of -map_metadata -1 with "-map_metadata:s -1 -map_metadata:g -1"

It appears "-map_chapters -1" still works, but is equal to "-map_metadata:c -1"

It could be nice to keep -map_metadata -1 functional as a similar shortcut. I don't know how widely it is used but I've sure used it a lot over the years and in lots of scripts.

[Thilo Borgmann]

Your commit was one off, actual regression is from
3c7dd5ed37da6d2de06c4850de5a319ca9cdd47f

Fix sent to the mailing list.

Thanks!

[Thilo Borgmann]

Fixed in 653ee3f159411a1b97c19b96393a39f29569ed99