<?php
	
	function replace_embedable_youtube_url($string) {
		$embed_html = "<iframe width=\"640\" height=\"360\" src=\"http://www.youtube.com/embed/%s\" frameborder=\"0\" allowfullscreen></iframe>";
		
		if(strlen($string) <= 0)
			return $string;
		
		$string_parts = explode(" ", $string);
		
		foreach($string_parts as $key => $value) {
			$parsed_string_parts = parse_url($string_parts[$key]);
			
			if(array_key_exists("host", $parsed_string_parts)) {
				switch($parsed_string_parts["host"]) {
					case "youtu.be": {
						$string_parts[$key] = sprintf($embed_html, $parsed_string_parts["path"]);
					} break;
					case ("youtube.com" || "www.youtube.com"): {
						$parsed_url_queries = array();
						$url_query_parts = explode("&", $parsed_string_parts["query"]);
						
						foreach($url_query_parts as $_key => $_value) {
							$query_parts = explode("=", $url_query_parts[$_key]);
							
							$parsed_url_queries[$query_parts[0]] = $query_parts[1];
						}
						
						if(array_key_exists("v", $parsed_url_queries))
							$string_parts[$key] = sprintf($embed_html, $parsed_url_queries["v"]);
					} break;
					default: {
						#@pass
					}
				}
			}
		}
		
		return implode(" ", $string_parts);
	}
	
	$string = "saintx http://youtu.be/zxlVvaIEhy0 http://youtube.com/watch?v=zxlVvaIEhy0 http://www.youtube.com/watch?v=zxlVvaIEhy0 saintx";
	
	print_r(
		array(
			"before" => $string,
			"after" => replace_embedable_youtube_url($string)
		)
	);