youtube.php

<?php
/**
 * YouTube Preg Match Test Case.
 *
 * @author Mario "Kuroir" Ricalde
 */

// Regular Expression (the magic).
$youtube_regexp = "/^http:\/\/(?:www\.)?(?:youtube.com|youtu.be)\/(?:watch\?(?=.*v=([\w\-]+))(?:\S+)?|([\w\-]+))$/";

// The test urls, one per line.
$urls = <<<EOF
http://www.youtube.com/watch?v=4-iI6UnKUCs&feature=grec_index
http://www.youtube.com/watch?v=4-iI6UnKUCs
http://www.youtube.com/watch?v=QNnz_ktVggQ&NR=1
http://youtu.be/QNnz_ktVAA
http://youtu.x
EOF;

// Turn each line into one single element in an array.
$urls = explode("\n", $urls);

foreach ($urls as $url) {
	// Match a URL.
	preg_match($youtube_regexp, $url, $matches);
	
	// Remove empty values from the array (regexp shit).
	$matches = array_filter($matches, function($var) {
		return($var !== '');
	});
	
	// If we have 2 elements in array, it means we got a valid url!
	// $matches[2] is the youtube ID!
	if (sizeof($matches) == 2) {
		var_dump($matches);
	}
}