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• Split a video to multiple chunks according to multiple starting and ending frame indices

  7 octobre 2015, par Jon

  Are there any tools (like FFmpeg or OpenCV) can split a video into multiple chunks according to some specific starting and ending frame indices ? For example, given (0,20),(21,33),(40,60)..., each tuple means a starting and ending frame indices pair for a chunk, and the neighbor chunks might not adjoin.

  Note that, the number of chunks might be large. For example, given a 1 hour video, there might be 1500 splits.

• Ffmpeg set duration using node-fluent-ffmpeg

  23 mai 2013, par Vprnl

  I'm really new to the world of ffmpeg so please excuses me if this is a stupid queston.

  I'm using the module Node-fluent-ffmpeg to stream a movie and convert it from avi to webm.
  So far so good (it plays the video), but I'm having trouble parsing the duration to the player. My ultimate goal is to be able to skip ahead in the movie. But first the player needs to know how long the video is.

  my code is as followed :

  var stat = fs.statSync(movie);
  
  
  
  var start = 0;
  
  var end = 0;
  
  var range = req.header('Range');
  
  if (range != null) {
  
  start = parseInt(range.slice(range.indexOf('bytes=')+6,
  
    range.indexOf('-')));
  
  end = parseInt(range.slice(range.indexOf('-')+1,
  
    range.length));
  
  }
  
  if (isNaN(end) || end == 0) end = stat.size-1;
  
  if (start > end) return;
  
  
  
  res.writeHead(206, { // NOTE: a partial http response
  
      'Connection':'close',
  
      'Content-Type':'video/webm',
  
      'Content-Length':end - start,
  
      'Content-Range':'bytes '+start+'-'+end+'/'+stat.size,
  
      'Transfer-Encoding':'chunked'
  
  });
  
  
  
  var  proc = new ffmpeg({ source: movie, nolog: true, priority: 1, timeout:15000})
  
      .toFormat('webm')
  
      .withVideoBitrate('1024k')
  
      .addOptions(['-probesize 900000', '-analyzeduration 0', '-bufsize 14000'])
  
      .writeToStream(res, function(retcode, error){
  
      if (!error){
  
          console.log('file has been converted succesfully',retcode);
  
      }else{
  
          console.log('file conversion error',error);
  
      }
  
  });

  I tried to set the header with a start and a end based on this article : http://delog.wordpress.com/2011/04/25/stream-webm-file-to-chrome-using-node-js/

  I also looked in the FFmpeg documentation and found -f duration and -ss.
  But I don't quite know how to convert the byte range to seconds.

  I feel like I'm pretty close to a solution but my inexperience with the subject matter prohibits me from getting it to work. If I'm unclear in any way please let me know. (I have a tendency of explaining things fuzzy.)

  Thanks in advance !

• Converting RGB images into lossless video with avconv / ffmpeg [migrated]

  19 mai 2013, par despens

  I am trying to convert a series of PNG24 images containing a screen animation to a lossless video, so that every pixel is reproduced exactly as it was in the original. But avconv (and ffmpeg) both produce the same, unsatisfying results, which seem to stem from a colospace conversion going wrong.

  This is the version of avconv I am using :

  avconv version 0.8.6-4:0.8.6-0ubuntu0.12.04.1, Copyright (c) 2000-2013 the Libav developers
  
    built on Apr  2 2013 17:02:36 with gcc 4.6.3

  Each of the images is 1280×800 pixels in size. They do not contain any photographic motives, but specially dithered patterns.

  I used the qtrle codec because apparently this is a lossless codec that works very much like animated GIFs or animated PNGs. However, during the conversion to video there seems to happen a color space conversion ("filter") that is messing with the pixels.

  This is the avconv output :

  $ avconv -f image2 -r 30 -i frames.png/wth-%08d.png -vcodec qtrle -pix_fmt rgb24 -t 15 qtrle-30fps-rgb.mov
  
  avconv version 0.8.6-4:0.8.6-0ubuntu0.12.04.1, Copyright (c) 2000-2013 the Libav developers
  
    built on Apr  2 2013 17:02:36 with gcc 4.6.3
  
  Input #0, image2, from 'frames.png/wth-%08d.png':
  
    Duration: 00:11:17.96, start: 0.000000, bitrate: N/A
  
      Stream #0.0: Video: png, bgra, 1280x800, 30 fps, 30 tbr, 30 tbn, 30 tbc
  
  File 'qtrle-30fps-rgb.mov' already exists. Overwrite ? [y/N] y
  
  [buffer @ 0x740a00] w:1280 h:800 pixfmt:bgra
  
  [avsink @ 0x742ac0] auto-inserting filter 'auto-inserted scaler 0' between the filter 'src' and the filter 'out'
  
  [scale @ 0x743680] w:1280 h:800 fmt:bgra -> w:1280 h:800 fmt:rgb24 flags:0x4
  
  Output #0, mov, to 'qtrle-30fps-rgb.mov':
  
    Metadata:
  
      encoder         : Lavf53.21.1
  
      Stream #0.0: Video: qtrle, rgb24, 1280x800, q=2-31, 200 kb/s, 30 tbn, 30 tbc
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (png -> qtrle)
  
  Press ctrl-c to stop encoding
  
  frame=  450 fps= 22 q=0.0 Lsize=  126056kB time=15.00 bitrate=68843.4kbits/s    
  
  video:126052kB audio:0kB global headers:0kB muxing overhead 0.003441%

  This is an original PNG image file :

  

  This is a screenshot of the video being replayed :

  

  Please note that you need to see these images in their original 1280×800 resolution to notice the differences.

  Here is a side-by-side comparison, with the left picture being the original and the right one the outcome after video encoding :

  

  Is there any way I can produce a truly lossless, pixel-perfect video file from a series of PNGs ?