If your templates_c/debug.txt shows "Create Thumbnail - START" as last line when uploading a video, the problem is with ffmpeg-php not able to create thumbnail.

To verify, download following script, unzip and upload to your server.

http://www.buyscripts.in/vshare/vshare_test.zip

Now access the url

http://yourdomain.extn/vshare_test/thumb.php