youtube-replace-url

gistfile1.php

function replaceLinkToIframe($text, $width = 480, $height = 390)
{
	$text = preg_replace('~
		# Match non-linked youtube URL in the wild. (Rev:20111012)
		https?://         # Required scheme. Either http or https.
		(?:[0-9A-Z-]+\.)? # Optional 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',
		'<a href="$0">watch video</a><div class="video-youtube" style="display:none"><iframe width="' . $width .'" height="' . $height .'" src="http://www.youtube.com/embed/$1" frameborder="0" allowfullscreen></iframe></div>',
		$text);
	return $text;
}