To verify download the script available at

http://www.buyscripts.in/tmp/thumb.phps


Find

$ff = $config[basedir]. "/video/90kb_1.wmv";

Replace with any existing video in video folder.

Rename the file to thumb.php, upload to your site and run it.

It should create following files.

thumb/288.jpg
thumb/1_288.jpg
thumb/2_288.jpg
thumb/3_288.jpg

On servers having problem, i have found it some times create thumb, some times not, proper reinstallation of ffmpeg/ffmpeg-php will fix the problem.