YouTube Regex

youtube-regex.php

<?php
$string = "<iframe width=\"1280\" height=\"720\" src=\"http://www.youtube.com/embed/UoVCqOlWMZg?rel=0&amp;hd=1\" frameborder=\"0\" allowfullscreen></iframe>";
preg_match_all( '~
	# Match non-linked youtube URL in the wild. (Rev:20110825)
	https?://				# Required scheme. Either http or https.
	(?:www\.)?				# Optional www subdomain.
	(?:					# Group host alternatives.
		youtu\.be/			# Either youtu.be,
		| youtube\.com			# or youtube.com followed by
		\S*				# Allow anything up to VIDEO_ID,
		[^\w\-\s]			# but char before ID is non-ID char.
	)					# End host alternatives.
	([\w\-]{11})				# $1: VIDEO_ID is exactly 11 chars.
	(?=[^\w\-]|$)				# Assert next char is non-ID or EOS.
	(?!					# Assert URL is not pre-linked.
		[?=&+%\w]*			# Allow URL (query) remainder.
		(?:				# Group pre-linked alternatives.
			[\'"][^<>]*>		# Either inside a start tag,
			| </a>			# or inside <a> element text contents.
		)				# End recognized pre-linked alts.
	)					# End negative lookahead assertion.
	[?=&+%\w]*				# Consume any URL (query) remainder.
	~ix', $string, $output_var );

print_r( $output_var );