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• pexpect.run() terminates before ending ffmpeg without finishing the conversion

  24 novembre 2012, par Davisein

  I'm working on a python script that does a custom conversion of videos via ffmpeg.

  My problem is that the execution of ffmpeg stops suddenly after a bit of conversion (usually 3-4 mb out of 100mb) with a None exit code.

  I'm using the pexpect library. Currently I do not check the progress but I will in a close future. It seems that I am right using pexpect regarding these questions FFMPEG and Pythons subprocess and Getting realtime output from ffmpeg to be used in progress bar (PyQt4, stdout). This is the command that I'm running (I have checked that it's exactly this one)

  nice ffmpeg -i '/full/path' -s 640x360 -strict experimental -vcodec libx264
  
     -f mp4 -  coder 0 -bf 0 -refs 1 -flags2 -wpred-dct8x8 -level 30 -crf 26
  
     -bufsize 4000k -maxrate 350k -preset medium -acodec libvo_aacenc
  
     -ar 48000.0 -ab 128K -threads 2 -y '/full/path/out'

  I am using nice but I have tried also without it and the result ends up being the same.

  I'm running pexpect this way :

  output, exit = pexpect.run(self.command(), withexitstatus=True,\
  
                                     logfile=logfile)
  
  print output
  
  print exit

  Of course I have tried the same command on the command line and it works fine.

  Any clue on what might be happening ?

• Getting length of video

  23 février 2017, par MZimmerman6

  I am having trouble finding a simple example of how to get the video length of a file programmatically. Many people say, oh use this library/wrapper or whatever, but do not say how. I have downloaded ffmpeg, but have no clue how to actually use it and there does not seem to be any example of how to use it to get the video duration. I see how you can use it to convert videos, but I simply just want to know the duration of a video. All of the other information does not matter.

  Is there any way of doing this simply, whether it be in C#, python, java, whatever, that will just return a string that indicates the length of a video file.

  Please provide examples if possible. Thanks in advance !

  Assume standard file formats, such as wmv, avi, mp4, mpeg. Stuff that has metadata.

• avcodec_decode_video2 takes long time to decode wmv

  22 février 2013, par Mike Versteeg

  I have written a player using the ffmpeg libraries that plays several avi, mp4 and mpg files fine but not wmv. Debugging has shown that the culprit is avcodec_decode_video2 which for some reason takes half a second to decode a single wmv frame. I have tested and confirmed this with multiple wmv files, even those with much lower resolution then other files that play successfully. Anyone has a clue what I'm doing wrong ?

  PS : log shows "Extra data : 8 bits left, value : 0" and "parser not found for codec wmav2, packets or times may be invalid." for WMV files.

  UPDATE :
  Further examination has shown the call to avcodec_decode_video2 is not slow, instead it seems to return the same frame some 16 times or so, giving the visual impression that it is slow. It does not return an error code so I have no clue why it won't decode all frames in the case of wmv.

  Relevant code :

    AVPacket packet;
  
    av_init_packet(&packet);
  
    done = pOwner->av_read_frame(pFormatCtx, &packet) < 0;
  
    if (!done && packet.stream_index==videostream) 
  
        bool error = pOwner->avcodec_decode_video2(pVCodecCtx, pFrameYUV, &finished, &packet) < 0;