$url = 'http://www.youtube.com/watch?v=jNQXAC9IVRw';
 
$parsed_url = parse_url($url);
parse_str($parsed_url['query'], $parsed_query);
echo '<iframe src="http://www.youtube.com/embed/' . $parsed_query['v'] . '" type="text/html" width="400" height="300" frameborder="0"></iframe>';