regex to get youtube id from embed code php code example

Example: php get youtube code from url

<?php
$url = "http://www.youtube.com/watch?v=C4kxS1ksqtw&feature=relate";
parse_str( parse_url( $url, PHP_URL_QUERY ), $my_array_of_vars );
echo $my_array_of_vars['v'];    
  // Output: C4kxS1ksqtw
?>