try uploading small video, bigger video need more CPU time, that is why youtube itself limit video size to 100 MB.

Since you are on shared hosting, CPU is shared by other sites, so big video convertion may be a problem.

Your php.ini settings are

max_execution_time 300 300
max_input_time 60 60
That is script execute for 200 seconds, if you upload big video it need more time to get converted into FLV format.

You may need to modify other php.ini settings too.