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• Interesting behavior in Media Source Extensions

  28 mai 2020, par newtonian_fig

  I'm trying to build a fairly standard video player using Media Source Extensions ; however, I want the user to be able to control when the player moves on to a new video segment. For example, we might see the following behavior :

  



  

  1. Video player plays 1st segment

  


  2. Source Buffer runs out of data causing the video to appear paused

  


  3. When the user is ready, they click a button that adds the 2nd segment to the Source Buffer

  


  4. The video continues by playing the 2nd segment

  


  



  This works well, except that when the video appears paused during step 2 it doesn't stop at the last frame of the 1st segment. Instead, it stops two frames before the end of the 1st segment. Those last two frames aren't being dropped, they just get played after the user clicks the button to advance the video. This is an issue for my application, and I'm trying to figure out a way to make sure all of the frames from the 1st segment get played before the end of step 2.

  



  I suspect that these last two frames are getting held up in the video decoder buffer. Especially since calling endOfStream() on my Media Source after adding the 1st segment to the Source Buffer causes the 1st segment to play all the way through with no frames left behind.

  



  Additional Info

  



  

  • I created each video segment file from a series of PNGs using the following ffmpeg command

  


  



  ffmpeg -i %04d.png -movflags frag_keyframe+empty_moov+default_base_moof video_segment.mp4

  



  

  • Maybe this is a clue ? End of stream situations not handled correctly (last frames are dropped)

  


  • Another interesting thing to note is that if the video only has 2 frames or less, MSE doesn't play it at all.

  


  • The browser I'm using is Chrome. The code for my MSE player is just taken from the Google Developers example, but I'll post it here for completeness. This code only covers up to step 2 since that's where the issue is.

  


  



  <code class="echappe-js">&lt;script&gt;&amp;#xA;const mediaSource = new MediaSource();&amp;#xA;video.src = URL.createObjectURL(mediaSource);&amp;#xA;mediaSource.addEventListener(&amp;#x27;sourceopen&amp;#x27;, sourceOpen, { once: true });&amp;#xA;&amp;#xA;function sourceOpen() {&amp;#xA;  URL.revokeObjectURL(video.src);&amp;#xA;  const sourceBuffer = mediaSource.addSourceBuffer(&amp;#x27;video/mp4; codecs=&quot;avc1.64001f&quot;&amp;#x27;);&amp;#xA;  sourceBuffer.mode = &amp;#x27;sequence&amp;#x27;;&amp;#xA;&amp;#xA;  // Fetch the video and add it to the Source Buffer&amp;#xA;  fetch(&amp;#x27;https://s3.amazonaws.com/bucket_name/video_file.mp4&amp;#x27;)&amp;#xA;  .then(response =&gt; response.arrayBuffer())&amp;#xA;  .then(data =&gt; sourceBuffer.appendBuffer(data));&amp;#xA;}&amp;#xA;&amp;#xA;&lt;/code&gt;&lt;/pre&gt;&amp;#xA;

• i want to convert a file of images and audio into video

  26 mai 2019, par ÄbdûlBåsįt Älį

  i want the step to use ff-mpeg . i am trying this
  import ffmpeg

  cmd = 'ff mpeg -y -i Audio.wav  -r 30 -i Video.h264  -filter:a aresample=async=1 -c:a flac -c:v copy av.mkv'
  
  subprocess.call(cmd, shell=True)                                     
  
  print('Muxing Done')

• Calculate frames to remove to get timelapse of desired length

  12 juin 2016, par Espen Birk

  I’ve got lots of images stored on a server, and a reference in a MySQL database so that i can easily query it for image from specific dates/time.

  Images is taken with an interval of 7 images/hour.

  Lets say i want to create a timelapse from the last 4 days, and make a 5 sec movie. How can i calculate how to evenly drop frames to get to that desired length of 5 seconds ?

  This is what i got so far.

  Total images : 4 Days * 24 hours * 7 images/hour = 672 images
  Required images at 24 fps : 24 * 5 = 120 images

  Divide the total images with the required images to find out which/every frame i need to keep

  672 / 120 = 5.6

  Then i loop trough all 672 images, and every 5th or 6th time i store a reference to the image in an array.

  Here is my problem. If i round up i get a video thats longer than i want, and if i round down i get a video thats shorter.

  If i keep every 5th image when looping : 134 images / 24 fps = 5.6 sec video
  If i keep every 6th image when looping : 112 images / 24 fps = 4.6 sec video

  Is it possible to get it better, and still skip images evenly ?

  Solved this using xxfelixxx’s answer in PHP
  Heres the code in PHP :

  $start  = 1;
  
  $stop   = 672; // Total Images
  
  
  
  $dur    = 5;   // Video Duration
  
  $n      = 24 * $dur; // Required frames - 24 FPS * Duration
  
  $next   = $start;
  
  $step = ( $stop - $start ) / $n;
  
  
  
  $frames = array();
  
  
  
  for ($i = 1; $i <= $n; $i++) {
  
      $frames[] = round($next);
  
      $next += $step;
  
  };
  
  
  
  var_dump($frames);