$r1 = '/^https?:\/\/(?:youtu\.be)\/([^?&#\/]+)/i';
$r2 = '/^https?:\/\/(?:www\.youtube\.com)\/(?:watch)?[?&#\/]*?v=([^?&#\/]+)[?&#\/]*?/i';

if(preg_match($r1, $this->link_youtube, $m) || preg_match($r2, $this->link_youtube, $m)){
    $this->link_youtube = 'http://www.youtube.com/embed/'.$m[1];
}