$re = '/https?:\/\/(?:[a-z0-9]+\.)?livestream\.com\/(?|(accounts\/[0-9]+\/events\/[0-9]+(?:\/videos\/[0-9]+)?)|[^\s\/]+\/video\?clipId=([^\s&]+)|([^\s\/]+))/';
$str = 'http://original.livestream.com/bethanychurchnh = bethanychurchnh
http://original.livestream.com/bethanychurchnh/video?clipId=flv_b54a694b-043c-4886-9f35-03c8008c23 = flv_b54a694b-043c-4886-9f35-03c8008c23
http://livestream.com/accounts/142499/events/3959775 = accounts/142499/events/3959775
http://livestream.com/accounts/142499/events/3959775/videos/83958146 = /accounts/142499/events/3959775/videos/83958146';
preg_match_all($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