$re = '/((?:https?:\/\/)?(?:www\.)?youtu\.?be(?:\.com)?\/(?!.*[?&]v=).*(?:list=)([\w-_]+)[^\s\'\"\.]*)/mi';
$str = 'https://www.youtube.com/playlist?list=PLFgquLnL59akaNTxtgsoKn4c0Q8utjqku
http://www.youtube.com/embed/videoseries?list=PLdwCuEoZ_6l6C47ciTvf6Z2GArUOCHHQ3
https://www.youtube.com/watch?v=VTMcqVFk39s&index=2&list=PLxgKRG5rfVFa067PHSpju_XaTPiyii31L
https://www.youtube.com/watch?v=TpbTkbv4L2Y&list=PLvqxe4XbcSiEzrZm28NjsLXmHkffCJmBY&index=2
https://www.youtube.com/watch?index=2&list=PLxgKRG5rfVFa067PHSpju_XaTPiyii31L&v=VTMcqVFk39s
';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php