When you upload, video is converted to FLV format for viewing in flash player. This is done by mencoder/ffmpeg.

Id you enabled debug in admin, you will be able to see debug information in templates_c/debug.txt file.

You will see the convertion command used some thing like

/usr/local/bin/mencoder /path/to/video/1.wmv -o /path/to/1.flv -of lavf -oac mp3lame -lameopts abr:br=56 -ovc lavc -lavcopts vcodec=flv:vbitrate=500:mbd=2:mv0:trell:v4mv:cbp:l ast_pred=3 -srate 22050 -lavfopts i_certify_that_my_video_stream_does_not_use_b_fram es
What you need to do is verify if this command works on your server.

If youtube clone requirements are not installed properly, you will see errors, in case of errors, you need to ask your server admin to check and fix youtube clone requirements installed on the server.

Now to run the command, you need to create a PHP file with following content.

Code:
<html>
<body bgcolor="Black" text="White">
<?php

error_reporting(E_ALL);

$convert_command = "REPLACE WITH YOUR CONVERT COMMAND FROM templates_c/debug.txt";

$var = exec($convert_command,$exec_result);

echo "<pre>";
for($i=0;$i<count($exec_result);$i++){
	echo $exec_result[$i] . "
";
}


?>
</body>
</html>

Name is convert.php and upload to your server and call it

http://yourdomain.extn/convert.php

You will see what is going on