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• Cutting movie with ffmpeg result in audio/video desync

  15 mai 2020, par T4ng10r

  I've concate long ago set of movies taken during some lecture. Now I want to cut them for each question/answer.

  



  I do it like this.

  



  


  ffmpeg -ss 00:00:34.7 -t 00:10:44.6 -y -i input_movie.mp4 -vcodec copy -acodec copy output_1.mp4

  
 


  ffmpeg -ss 00:11:22.2 -y -i input_movie.mp4 -vcodec copy -acodec copy output_2.mp4

  


  



  Yet, for the second part I can't set proper starting point so audio and video would be in sync.
  
Usually I could fix it with small tweeks in cut start time (like .1, .2, and so on). For this case this doesn't work.
  
When I play second cut in mplayer video is few second behind audio (where audio is cut properly). When I jump forward and back - all is again in sync.

  



  Where's the problem ? How to fix it ?

  


• 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 ?

• How to convert jquery animation to movie or gif format ?

  19 avril 2019, par Barış Demirdelen

  How to convert jquery animation to movie or gif format ?
  Animation and screenshot functions call or too slow.
  Help me please

  Animation Function

  function resim1(){
  
      $("#resim-1").animate({ left: leftx}, startEffectTime1);
  
      ......
  
  }

  ScreenShot Function but too slow

  function shot(){
  
            html2canvas($("#main"), {
  
                onrendered: function(canvas) {
  
                    theCanvas = canvas;
  
                    document.body.appendChild(canvas);
  
                    Canvas2Image.saveAsPNG(canvas); 
  
                    $("#img-out").append(canvas);
  
                }
  
            });
  
  }

  Call animation and screenshot functions

  $(document).ready(function() {
  
       resim1(); // Animate start
  
       setInterval(function(){ // Screenshot start
  
            shot();
  
       },500);
  
  
  
  });

  Bottom function call animation breaking :/

  $(document).ready(function() {
  
       resim1(); // Animate start
  
       setInterval(function(){ // Screenshot start
  
            shot();
  
       },500);
  
  
  
  });