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• Why does calling ffmpeg from python's popen break screen capture functionality ?

  4 mars 2016, par Jabb

  I am trying to create screen captures from mp4 files in python.
  Calling ffmpeg on the command line works fine. But as soon, as I issue the same command through python "popen", functionality breaks with an error that ffmpeg cannot find the moov atom. Can anyone explain this to me ?

  This is how I call ffmpeg from python :

  def ffmpegGetScreenshot(self,inputFilename,index,startTime):
  
      my_env = os.environ.copy()
  
      my_env.update({'PATH': '/bin:/usr/bin:/sbin:/usr/sbin:/usr/local/bin:/bin:/usr/bin:/sbin:/usr/sbin:/usr/local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin'})
  
  
  
      filename = inputFilename.split("/")[1]
  
      directory = inputFilename.split("/")[0]
  
      if os.path.isfile('videoscreenshots/'+filename+"_cs"+str(index)+".jpg"):
  
          return 'videoscreenshots/'+filename+"_cs"+str(index)+".jpg"
  
      print "get screenshots for: " + inputFilename
  
      command = [ FFMPEG_BIN,
  
                  '-y', 
  
                  '-i', inputFilename,
  
                  '-ss', str(int(startTime)),
  
                  '-vframes', '1',
  
                  #'-loglevel','quiet',
  
                  'videoscreenshots/'+filename+"_cs"+str(index)+".jpg"
  
                  ]
  
      pipe = sp.Popen(command, env=my_env,stdin = sp.PIPE,stdout = sp.PIPE, stderr=None)
  
      print command
  
  
  
      return 'videoscreenshots/'+filename+"_cs"+str(index)+".jpg"

  Result :

  ffmpeg version 2.7.2 Copyright (c) 2000-2015 the FFmpeg developers
  
    built with gcc 4.9.2 (Debian 4.9.2-10)
  
    configuration: --enable-gpl --enable-postproc --enable-swscale --enable-avfilter --enable-libmp3lame --enable-libvorbis --enable-libtheora --enable-libx264 --enable-libspeex --enable-shared --enable-pthreads --enable-libopenjpeg --enable-libfaac --enable-nonfree
  
    libavutil      54. 27.100 / 54. 27.100
  
    libavcodec     56. 41.100 / 56. 41.100
  
    libavformat    56. 36.100 / 56. 36.100
  
    libavdevice    56.  4.100 / 56.  4.100
  
    libavfilter     5. 16.101 /  5. 16.101
  
    libswscale      3.  1.101 /  3.  1.101
  
    libswresample   1.  2.100 /  1.  2.100
  
    libpostproc    53.  3.100 / 53.  3.100
  
  [mov,mp4,m4a,3gp,3g2,mj2 @ 0x652120] moov atom not found
  
  videochunks/test.mp4: Invalid data found when processing input
  
  test.mp4

  This is the same command called on the console

  /usr/local/bin/ffmpeg -y -i videochunks/test.mp4 -ss 9 -vframes 1 videoscreenshots/test.mp4_cs2.jpg

  Result :

  root@3:/app# /usr/local/bin/ffmpeg -y -i videochunks/test.mp4 -ss 9 -vframes 1 videoscreenshots/test.mp4_cs2.jpg
  
  ffmpeg version 2.7.2 Copyright (c) 2000-2015 the FFmpeg developers
  
    built with gcc 4.9.2 (Debian 4.9.2-10)
  
    configuration: --enable-gpl --enable-postproc --enable-swscale --enable-avfilter --enable-libmp3lame --enable-libvorbis --enable-libtheora --enable-libx264 --enable-libspeex --enable-shared --enable-pthreads --enable-libopenjpeg --enable-libfaac --enable-nonfree
  
    libavutil      54. 27.100 / 54. 27.100
  
    libavcodec     56. 41.100 / 56. 41.100
  
    libavformat    56. 36.100 / 56. 36.100
  
    libavdevice    56.  4.100 / 56.  4.100
  
    libavfilter     5. 16.101 /  5. 16.101
  
    libswscale      3.  1.101 /  3.  1.101
  
    libswresample   1.  2.100 /  1.  2.100
  
    libpostproc    53.  3.100 / 53.  3.100
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'videochunks/test.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      title           : Test
  
      composer        : Test
  
      album           : Test
  
      encoder         : Lavf56.36.100
  
    Duration: 00:00:10.01, start: 0.000000, bitrate: 520 kb/s
  
      Stream #0:0(und): Video: h264 (Constrained Baseline) (avc1 / 0x31637661), yuv420p, 320x240 [SAR 4:3 DAR 16:9], 436 kb/s, 25 fps, 25 tbr, 25k tbn, 50 tbc (default)
  
      Metadata:
  
        handler_name    : VideoHandler
  
      Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 97 kb/s (default)
  
      Metadata:
  
        handler_name    : SoundHandler
  
  [swscaler @ 0x648260] deprecated pixel format used, make sure you did set range correctly
  
  Output #0, image2, to 'videoscreenshots/test_cs2.jpg':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      title           : Test
  
      composer        : Test
  
      album           : Test
  
      encoder         : Lavf56.36.100
  
      Stream #0:0(und): Video: mjpeg, yuvj420p(pc), 320x240 [SAR 4:3 DAR 16:9], q=2-31, 200 kb/s, 25 fps, 25 tbn, 25 tbc (default)
  
      Metadata:
  
        handler_name    : VideoHandler
  
        encoder         : Lavc56.41.100 mjpeg
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (h264 (native) -> mjpeg (native))
  
  Press [q] to stop, [?] for help
  
  frame=    1 fps=0.0 q=3.9 Lsize=N/A time=00:00:00.04 bitrate=N/A
  
  video:11kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown

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