Add this code to your functions.php file:

/*-----------------------------------------------------------------------------------*/
/* ADD F4V UPLOADS TO THE WP ADMIN
/*-----------------------------------------------------------------------------------*/
// Add mimi types to function get_allowed_mime_types
function add_allowed_mime_types($mimes) {
 $my_new_mimes = array (
 'f4v' => 'video/mp4'
 );
 return array_merge($mimes,$my_new_mimes);
}
add_filter('upload_mimes','add_allowed_mime_types');

// Add an extension to (2) function wp_ext2type
function add_ext2_ext2type($ext) {
 $my_new_extensions = array (
 'video' => array( 'f4v' )
 );
 return array_merge($ext,$my_new_extensions);
}
add_filter('upload_mimes','add_ext2_ext2type');