PHP从FLV文件获取视频预览图的方法

<?php
// references http://www.longtailvideo.com/support/forum/modules/12661/external-php-with-ffmpeg-using-readfile-
// generate a preview image from an flv file on-the-fly, or to save
// call with: ffmpeg_image.php?file=video.flv&time=00:00:05&browser=true
// call with: ffmpeg_image.php?file=video.flv&percent=75.3&browser=true
// no time defaults to "00:00:01" (one second), no browser defaults to "true"
$videofile = (isset($_get['file'])) ? strval($_get['file']) : 'video.flv';
$image = substr($videofile, 0, strlen($videofile) - 4);
$time = (isset($_get['time'])) ? strval($_get['time']) : '00:00:01';
// debug ("  file: ", $videofile);
// debug (" image: ", $image);
// debug ("  time: ", $time);
// check time format
if (!preg_match('/\d\d:\d\d:\d\d/', $time))
{
  $time = "00:00:00";
}
if (isset($_get['percent']))
{
  $percent = $_get['percent'];
// debug (" percent: ", $percent);
  ob_start();
  exec("/usr/bin/ffmpeg -i \"". $videofile . "\" 2>&1");
  $duration = ob_get_contents();
  ob_end_clean();
  // debug ("duration: ", $duration);
  preg_match('/duration: (.*?),/', $duration, $matches);
  $duration = $matches[1];
// debug ("duration: ", $duration);
  $duration_array = split(':', $duration);
  $duration = $duration_array[0] * 3600 + $duration_array[1] * 60 + $duration_array[2];
  $time = $duration * $percent / 100;
// debug (" time: ", $time);
  $time = intval($time/3600) . ":" . intval(($time-(intval($time/3600)*3600))/60) . ":" . sprintf("%01.3f", ($time-(intval($time/60)*60)));
// debug (" time: ", $time);
}
$browser = (isset($_get['browser'])) ? strval($_get['browser']) : 'true';
// debug (" browser: ", $browser);
if ($browser == "true")
{
  header('content-type: image/png');
  exec("/usr/bin/ffmpeg -vcodec png -i \"" . $videofile . "\" -ss " . $time . " -vframes 1 -f image2 -");
//header('content-type: image/jpeg');
//exec("/usr/bin/ffmpeg -vcodec mjpeg -i \"" . $videofile . "\" -ss " . $time . " -vframes 1 -f image2 -");
}
else
{
  exec("/usr/bin/ffmpeg -vcodec png -i \"" . $videofile . "\" -ss " . $time . " -vframes 1 -f image2 \"" . $image . "\"%d.png");
//exec("/usr/bin/ffmpeg -vcodec mjpeg -i \"" . $videofile . "\" -ss " . $time . " -vframes 1 -f image2 \"" . $image . "\"%d.jpg");
}
?>