WordPress: YouTube shortcode

shortcode-youtube.css

// http://embedresponsively.com/
.embed-container { 
	position: relative;
	padding-bottom: 56.25%;
	height: 0;
	overflow: hidden;
	max-width: 100%;
	height: auto;
	margin-bottom: 1.5em;
}
.embed-container iframe,
.embed-container object,
.embed-container embed {
	position: absolute;
	top: 0;
	left: 0;
	width: 100%;
	height: 100%;
}

shortcode-youtube.php

function kj_youtube($a) {
	extract(shortcode_atts(array(
		'url'	=> 'http://www.youtube.com/watch?v=A1P_nRxZXl4'
	), $a));

	// globals for Open Graph use
	global $youtube_id;
	global $youtube_thumbnail;
	global $youtube_url;
	global $youtube_url_secure;

	// http://stackoverflow.com/a/9102270
	preg_match("/^.*(youtu.be\/|v\/|u\/\w\/|embed\/|watch\?v=|\&v=)([^#\&\?]*).*/", $url, $matches);

	if( isset($matches[2]) ){
		$youtube_id = $matches[2];
		$youtube_thumbnail = "http://img.youtube.com/vi/$youtube_id/hqdefault.jpg";
		$youtube_url = "http://www.youtube.com/v/$youtube_id";
		$youtube_url_secure = "https://www.youtube.com/v/$youtube_id";

		$url = "http://www.youtube.com/embed/$youtube_id";
	}
	
	return "<div class='embed-container'><iframe src='$url' frameborder='0' allowfullscreen></iframe></div>";
}

add_shortcode('youtube', 'kj_youtube');