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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

• FFMPEG -filter_complex is not generating desired output

  24 octobre 2017, par Mubbashar

  I am trying to
  embed subtitle at the bottom of video and
  add image/text watermark at the top right corner of video and
  add text at the top and bottom and
  add colored padding at top and bottom of video in the same command

  This following is the command I can get somewhat working. This is adding padding at the bottom but not at the top. It is successfully embedding subtitles in the video though.
  It is also disturbing some parts of the video, pushing them to the top and cropping the top of video (because of padding at the bottom I think) but some parts of the video are in place and are ok.

  I tried to write the command and use filter complex in FFMPEG but i am not sure how to use them correctly. Can somebody guide how to fix this and use filter complex correctly as documentation is too complex

  COMMAND

  ffmpeg -y -i video-orignal.mp4 -i watermark.jpg -filter_complex "[0:v]pad=iw:ih+300:0:0:purple[padded]; [padded]overlay=main_w-overlay_w-5:5[watermarked]; [0:v][watermarked]overlay=W-w-10:H-h-10,subtitles=subtitles-final.ass[out]" -map "[out]" -map 0:a video-final.mp4

• FFMPEG concat causing audio glitches in segments boundaries

  28 mai 2017, par Idan

  I am segmenting a video file to 10sec segments, transcoding each of them and then run a concat to merge them all back together.
  While the whole process works without errors and the final file is valid and playable, I’ve noticed some sort of glitches/interruptions in the audio stream when passing over the original segments boundaries.

  For example, in a 60sec video that was segmented to 10sec segments and stitched back again, the final output will show audio interruptions in 10/20/30/40/50 sec timestamps.

  For segmenting the files I use :

  ffmpeg -y -i $INPUT_FILE -c copy -flags -global_header -segment_time 10 -break_non_keyframes 0 -reset_timestamps 1 -segment_list file_segs.list -segment_list_type ffconcat -write_empty_segments 0 -segment_format mp4  -f segment file_seg-%d.mp4

  And for concat I use :

  ffmpeg -y -f concat -i file_segs.list -c copy -movflags +faststart file_video.mp4

  Transcoding is to libx264 / aac

  What might be the cause ? Is there any way to work around this problem ?