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• ffmpeg implicitly shifts video and audio

  2 mars 2020, par ynn

  I separated a .mkv file with audio and video into two files by the following command.

  ffmpeg -i input.mkv -vn -codec copy out.wav #extract audio
  
  ffmpeg -i input.mkv -an -codec copy out.mkv #extract video

  And I just merge them into one .mkv file :

  ffmpeg -i out.mkv -i out.wav -codec copy final.mkv #this behaves quite strangely

  I thought the initial input input.mkv and the final output final.mkv should be exactly the same, but, in final.mkv, the video and the audio was shifted by about five seconds. Using ffprobe, I found the cause was the video part (out.mkv) was trimmed off by the length (i.e. five seconds) for no reason.

  What’s happening here ? How can I avoid this strange shift ?

  ---

  Detailed Explanation :

  Hereafter I use this sample input called input.mkv. First, extract video and audio from it.

  $ ffmpeg -i input.mkv -vn -codec copy out.wav
  
  $ ffmpeg -i input.mkv -an -codec copy out.mkv

  Next, check the duration of them.

  $ ffprobe -i out.wav 2>&1 | grep Duration
  
    Duration: 00:00:18.88, bitrate: 1536 kb/s
  
  $ ffprobe -i out.mkv 2>&1 | grep Duration
  
    Duration: 00:00:18.87, start: 0.000000, bitrate: 1877 kb/s

  Then combine them.

  $ ffmpeg -i out.mkv -i out.wav -codec copy final.mkv

  Finally, check the duration of streams.

  $ ffprobe -i final.mkv 
  
  Input #0, matroska,webm, from 'final.mkv':
  
    Metadata:
  
      ENCODER         : Lavf58.29.100
  
    Duration: 00:00:18.88, start: 0.000000, bitrate: 3414 kb/s
  
      Stream #0:0: Video: h264 (High), yuv420p(tv, bt709, progressive), 900x586 [SAR 1:1 DAR 450:293], 30.30 fps, 30.30 tbr, 1k tbn, 60 tbc (default)
  
      Metadata:
  
        DURATION        : 00:00:18.866000000
  
      Stream #0:1: Audio: pcm_s16le, 48000 Hz, 2 channels, s16, 1536 kb/s
  
      Metadata:
  
        DURATION        : 00:00:18.880000000

  Strangely, duration of the video stream has been trimmed off from 18.8700 to 18.8660, though the length of the audio stream is not touched at all.

  It seems the longer the video is, the bigger part is trimmed. (In my case of a one hour video, no less than five seconds were trimmed off.)

  ---

  Version Information :

  ~ $ ffmpeg -version
  
  ffmpeg version n4.2.2 Copyright (c) 2000-2019 the FFmpeg developers
  
  built with gcc 9.2.1 (Arch Linux 9.2.1+20200130-2) 20200130
  
  configuration: --prefix=/usr --disable-debug --disable-static --disable-stripping --enable-fontconfig --enable-gmp --enable-gnutls --enable-gpl --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libdav1d --enable-libdrm --enable-libfreetype --enable-libfribidi --enable-libgsm --enable-libiec61883 --enable-libjack --enable-libmfx --enable-libmodplug --enable-libmp3lame --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libv4l2 --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxcb --enable-libxml2 --enable-libxvid --enable-nvdec --enable-nvenc --enable-omx --enable-shared --enable-version3
  
  libavutil      56. 31.100 / 56. 31.100
  
  libavcodec     58. 54.100 / 58. 54.100
  
  libavformat    58. 29.100 / 58. 29.100
  
  libavdevice    58.  8.100 / 58.  8.100
  
  libavfilter     7. 57.100 /  7. 57.100
  
  libswscale      5.  5.100 /  5.  5.100
  
  libswresample   3.  5.100 /  3.  5.100
  
  libpostproc    55.  5.100 / 55.  5.100

• Revision 36037 : s’assurer que la class ffmpeg_movie est disponible sinon cela ne sert pas ...

  9 mars 2010, par kent1@… — Log

  s’assurer que la class ffmpeg_movie est disponible sinon cela ne sert pas à grand chose

• ffmpeg codec error on audio file

  31 juillet 2013, par foosion

  I have some m4a files that will not play properly using the google music player app on my Android phone, although they play fine on most everything else. I thought the problem was the container and thought "ffmpeg -i bad.m4a -codec copy good.m4a" might help. However, when I run on the problem files, I get error messages. Running this command on non-problem files has not generated error messages.

  Please suggest ways to fix (other than re-encoding).

      [D:\temp\dl]ffmpeg -i "01 - The Day Begins.m4a" -codec copy day.m4a
  
  ffmpeg version N-55066-gc96b3ae Copyright (c) 2000-2013 the FFmpeg developers
  
    built on Jul 29 2013 18:05:45 with gcc 4.7.3 (GCC)
  
    configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-av
  
  isynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enab
  
  le-iconv --enable-libass --enable-libbluray --enable-libcaca --enable-libfreetyp
  
  e --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame --ena
  
  ble-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-l
  
  ibopus --enable-librtmp --enable-libschroedinger --enable-libsoxr --enable-libsp
  
  eex --enable-libtheora --enable-libtwolame --enable-libvo-aacenc --enable-libvo-
  
  amrwbenc --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxavs --
  
  enable-libxvid --enable-zlib
  
    libavutil      52. 40.100 / 52. 40.100
  
    libavcodec     55. 19.100 / 55. 19.100
  
    libavformat    55. 12.102 / 55. 12.102
  
    libavdevice    55.  3.100 / 55.  3.100
  
    libavfilter     3. 82.100 /  3. 82.100
  
    libswscale      2.  4.100 /  2.  4.100
  
    libswresample   0. 17.103 /  0. 17.103
  
    libpostproc    52.  3.100 / 52.  3.100
  
  [mov,mp4,m4a,3gp,3g2,mj2 @ 00000000002da300] stream 0, timescale not set
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '01 - The Day Begins.m4a':
  
    Metadata:
  
      major_brand     : m4a
  
      minor_version   : 0
  
      compatible_brands: M4A mp4isom
  
      creation_time   : 2003-07-06 20:27:46
  
      track           : 1
  
      genre           : Rock
  
      title           : The Day Begins
  
      artist          : Moody Blues
  
      album           : Days of Future Passed
  
      date            : 1967
  
    Duration: 00:05:50.83, start: 0.000000, bitrate: 166 kb/s
  
      Stream #0:0(eng): Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 15
  
  9 kb/s
  
      Metadata:
  
        creation_time   : 2003-07-06 20:27:46
  
        handler_name    : Apple Sound Media Handler
  
      Stream #0:1(eng): Data: none (mp4s / 0x7334706D)
  
      Metadata:
  
        creation_time   : 2003-07-06 20:27:46
  
        handler_name    : Apple MPEG-4 Scene Media Handler
  
      Stream #0:2(eng): Data: none (mp4s / 0x7334706D)
  
      Metadata:
  
        creation_time   : 2003-07-06 20:27:46
  
        handler_name    : Apple MPEG-4 ODSM Media Handler
  
      Stream #0:3: Video: png, rgb24, 240x240 [SAR 2834:2834 DAR 1:1], 90k tbr, 90
  
  k tbn, 90k tbc
  
  [ipod @ 000000000031dd40] track 0: could not find tag, codec not currently suppo
  
  rted in container
  
  Output #0, ipod, to 'day.m4a':
  
    Metadata:
  
      major_brand     : m4a
  
      minor_version   : 0
  
      compatible_brands: M4A mp4isom
  
      date            : 1967
  
      track           : 1
  
      genre           : Rock
  
      title           : The Day Begins
  
      artist          : Moody Blues
  
      album           : Days of Future Passed
  
      encoder         : Lavf55.12.102
  
      Stream #0:0: Video: png, rgb24, 240x240 [SAR 2834:2834 DAR 1:1], q=2-31, 90k
  
   tbn, 90k tbc
  
      Stream #0:1(eng): Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo, 159 kb/s
  
  
  
      Metadata:
  
        creation_time   : 2003-07-06 20:27:46
  
        handler_name    : Apple Sound Media Handler
  
  Stream mapping:
  
    Stream #0:3 -> #0:0 (copy)
  
    Stream #0:0 -> #0:1 (copy)
  
  Could not write header for output file #0 (incorrect codec parameters ?): Error
  
  number -1 occurred