gistfile1.php

<?php

  $GIF_SIZE_WIDTHxHEIGHT = "80x45";
  $DURATION_SECS = 6;
  $FIRST_FRAME_NUM = 41;
  $FRAME_SKIP = 1;
  $PREROLL_SECS = 2;

  foreach (glob("*.{mp4}", GLOB_BRACE) as $named)
    {
      $src = substr($named,0,-4);
      
      MP4ToAnimatedGIF($src, $GIF_SIZE_WIDTHxHEIGHT, $DURATION_SECS, $FIRST_FRAME_NUM, $FRAME_SKIP, $PREROLL_SECS);
    }

  function MP4ToAnimatedGIF ($mp4, $sizeXxY, $duration_seconds, $first_frame, $frame_skip, $preroll_seconds)
    {
      $TMP_DIRECTORY = "anim~";

      mkdir($TMP_DIRECTORY);

      @exec("ffmpeg -ss 0:00:$preroll_seconds -i $mp4.mp4 -t 0:0:".($duration_seconds*2)." -s $sizeXxY -f image2 $TMP_DIRECTORY/%03d.png");

      $cmdline = "convert -coalesce -layers OptimizeTransparency +map ";

      $last_frame = $duration_seconds * 29; // Assume 29.997 NTSC FPS
      
      $frame_files_included = "";
  
      while ($first_frame < $last_frame)
        {
          $frame_files_included .= $TMP_DIRECTORY."/".substr(sprintf('%03d', $first_frame),-3,3).".png ";

          $first_frame += $frame_skip;
        }
    
      $cmdline .= $frame_files_included;

      $cmdline .= "$mp4.gif";
  
      @exec($cmdline);

      rrmdir($TMP_DIRECTORY);
    }

  function rrmdir($dir)
    {
      foreach(glob($dir. "/*") as $file)
        {
          if(is_dir($file))
            rrmdir($file);
          else
            unlink($file);
        }

      rmdir($dir);
    }

?>