To upload big video files, you need to edit php.ini file in your server.

You can try following values

max_execution_time = 600
max_input_time = 600
memory_limit = 32M
register_globals = On
post_max_size = 800M
file_uploads = On
upload_max_filesize = 800M
If you are on shared hosting with no access to php.ini, try adding following line to .htaccess file

php_value max_input_time 600
php_value max_execution_time 600
php_value post_max_size 200M