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• ffmpeg merge silent video with another video+audio

  4 mars 2016, par Mark Dagger

  I want to create, in a single command, a video from 3 sources :

  1. a silent background video ;
  2. a smaller video to be overlayed (same length of 1), KEEPING its AUDIO ;
  3. a PNG logo to be overlayed

  I can create the video but cannot get the audio track. I don’t understand if -vf is supposed to work in this case. This is what I’ve tried to do :

  ffmpeg.exe -y -i MASTER_SILENT_VIDEO.mp4 -vf "movie=SMALLER_VIDEO_WITH_AUDIO.flv, scale=320:-1[inner];movie=MY_LOGO.png[inner2]; [in][inner] overlay=800:480,amerge [step1]; [step1][inner2] overlay=30:30 [out]" completed.mp4

  The "amerge" filter should do the audio merging job, but of course it doesn’t work. I’ve found similar questions involving -map or filtergraph but they refer to mixing a video source and an audio source ; I tried several filtergraph examples without success. Any idea ?

• Generating random thumbnails with PHP+FFMPEG

  30 décembre 2014, par MrGhost

  I’m trying to generate thumbnails from random points in a movie using FFMPEG and FFMPEG-PHP extension.

  My script works OK.. however takes 20 minutes just to generate 5-10 thumbnails !!

  The script works by generating random numbers which are used as frame numbers later. All numbers generated are within the movies frame count.

  Can you work out why this script is taking 20 mins to finish ?
  If not, a better solution ?

  <?php
  
  
  
  //Dont' timeout
  
  set_time_limit(0);
  
  
  
  //Load the file (This can be any file - still takes ages) 
  
  $mov = new ffmpeg_movie('1486460.mp4');
  
  
  
  //Get the total frames within the movie
  
  $total_frames = $mov->getFrameCount();
  
  
  
  //Loop 5-10 times to generate random frames 5-10 times
  
  for ($i = 1; $i <= 5; ) {
  
      // Generate a number within 200 and the total number of frames.
  
   $frame = mt_rand(200,$total_frames);
  
   $getframe = $mov->getFrame($frame);
  
   // Check if the frame exists within the movie
  
   // If it does, place the frame number inside an array and break the current loop
  
   if($getframe){
  
    $frames[$frame] = $getframe ;
  
    $i++;
  
   }
  
  }
  
  
  
  //For each frame found generate a thumbnail
  
  foreach ($frames as $key => $getframe) {
  
   $gd_image = $getframe->toGDImage();
  
   imagejpeg($gd_image, "images/shot_".$key.'.jpeg');
  
   imagedestroy($gd_image);
  
   echo $key.'<br />';
  
  }
  
  
  
  ?>

  The script SHOULD be generating frame numbers which are valid ? Anything within START - END should be valid frame numbers ? Yet the loop takes ages !

• Converting AC3 to AAC with minimal loss [on hold]

  20 juin 2016, par forthrin

  iPad does not seem to support the ac3 audio codec.

  Therefore, I am converting an mkv/h264/ac3 movie into m4v/m264/aac using ffmpeg to view it on the iPad.

  The video part is simply copied as it is ; my question is how I preserve the audio as best possible.

  1. Is there any way to do the audio conversion losslessly ?

  2. If no to question 1, what is the best way to preserve the audio quality ? If the source audio is 192 kb/s and 48000 Hz, should I simply use 192/48000 for the target too ? Or will I preserve the audio better if I increase the the bit rate somewhat ?

  3. Side question : I noticed that a lot of mkv files have rather poor audio to begin with. Will the loss of ac3/aac re-encoding be negligable compared to the initial quality loss from the source material ? And why isn’t high audio quality more of a priority for movie files ? It’s not like file sizes matter much anymore with today’s storage and bandwidth.