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• Split a movie into 1000+ shots using PyAV in a single pass ?

  3 mai 2019, par Andrew Klaassen

  I need to split a 44 minute MP4 into 1000 shots (i.e. separate MP4s) with ffmpeg. I want to do it quickly (i.e. in a single pass rather than 1000 passes), I need perfect frame accuracy, and I need to do it in Windows.

  The Windows command-line length limit is stopping me from doing this, and I’m wondering if someone could show me an example of how to do this using a library like PyAV or Avpy. (Libraries like ffmpeg-python and ffmpy won’t help, since they simply construct an ffmpeg command line and run it, leading to the same Windows command-line length issue that I already have.)

  After much testing and gnashing of teeth, I’ve learned that the only way to get perfect frame accuracy from ffmpeg, 100% of the time, is to use the "select" filter. ("-ss" in the newest versions of ffmpeg is frame accurate 99% of the time ; unfortunately, that’s not good enough for this application.)

  There are two ways to use "select" for this. There’s the slow way, which I’m doing now, and which requires having ffmpeg open the file 1000 times :

  for (start, end, name) in shots:
  
      audio_start = start / frame_rate
  
      audio_end = end + 1 / frame_rate
  
      cmd = [
  
          path_to_ffmpeg,
  
          '-y',
  
          '-i', input_movie,
  
          '-vf', r'select=between(n\,%s\,%s),setpts=PTS-STARTPTS' % (start, end),
  
          '-af', 'atrim=%s:%s,asetpts=PTS-STARTPTS' % (audio_start, audio_end),
  
          '-c:v', 'libx264',
  
          '-c:a', 'aac',
  
          '-write_tmcd', '0',
  
          '-g', '1',
  
          '-r', str(frame_rate),
  
          name + '.mp4',
  
          '-af', 'atrim=%s:%s' % (audio_start, audio_end),
  
          name + '.wav',
  
      ]
  
      subprocess.call(cmd)

  And there’s the fast way, which causes the Windows command line to explode when there are too many shots. The long command line leads to a failure to run :

  cmd = [
  
      path_to_ffmpeg,
  
      '-y',
  
      '-i',
  
      input_movie,
  
  ]
  
  for (start, end, name) in shots:
  
      audio_start = start / frame_rate
  
      audio_end = end + 1 / frame_rate
  
      cmd.extend([
  
          '-vf', r'select=between(n\,%s\,%s),setpts=PTS-STARTPTS' % (start, end),
  
          '-af', 'atrim=%s:%s,asetpts=PTS-STARTPTS' % (audio_start, audio_end),
  
          '-c:v', 'libx264',
  
          '-c:a', 'aac',
  
          '-write_tmcd', '0',
  
          '-g', '1',
  
          '-r', str(frame_rate),
  
          name + '.mp4',
  
          '-af', 'atrim=%s:%s' % (audio_start, audio_end),
  
          name + '.wav',
  
      ]
  
  subprocess.call(cmd)

  I’ve looked through the documentation of PyAV and Avpy, but I haven’t been able to figure out whether the second form of my function is something I could do there, or how I’d go about doing it. If it is possible, would someone be able to write a function equivalent to my second function, using either library ?

• FFMPEG Increment filename past 1000 and reset from 1

  15 avril 2019, par Eric Gao

  From the documentation :

  ffmpeg -i video.webm image-%03d.png

  This will extract 25 images per second from the file video.webm and save them as image-000.png, image-001.png, image-002.png up to image-999.png. If there are more than 1000 frames then the last image will be overwritten with the remaining frames leaving only the last frame.

  Is there any way to increment this number past 1000, and can I also have this restart from 1 so that we’re not just overwriting the last frame ?

  I have a script that analyzes these images as they come in so I use locally stored images as a buffer/queue. It’s also useful for me to have more images stored so I can go back and debug anything, so being able to do the above would be quite helpful for me.

• Mix more then 1000 mp3's sounds bad / Can I use FFmpeg to merge 1000 mp3s ?

  7 avril 2022, par maesbn

  I am working on a project where everybody has to activate a part of a song. I have about 7000 mp3's, each with the same length of the final mix but with only a small part of audio. So for example you can hear a drum hit at the 15th second and the rest of the mp3 (about 4 min.) is silence.

  



  I use the mix filter to add all the mp3's. I add them 32 mp3s at a time. 
The first test I've run results in the first mixed mp3s to be silenced ? (I set the Volume on the mix to the number of tracks) Also the sound is of poor quality after the mix. Can I fix this ?

  



  Or do you think this can not be done by ffmpeg ? Do you know an alternative program to do this ?

  



  Thanks !
B.