Fluid width YouTube videos of different aspect ratios, by Chris Coyier

jquery.fluid-youtube-videos-original.js

// Original code from http://css-tricks.com/examples/FluidWidthYouTube/iframe.php

$(function() {

	// find all videos
	var allVideos = $("iframe[src^='http://www.youtube.com']"),

	    // The thing that is fluid width
	    body = $("body"),

	    // used to cache "this"
	    el;

	// figure out and save aspect ratio for each video
	allVideos.each(function() {

		// cache
		el = $(this);

		el
			// store aspect ratio as data
			.data('aspectRatio', el.attr('height') / el.attr('width'))

			// and remove the hard coded width/height
			.removeAttr('height')
			.removeAttr('width');

	});

	// when window is resized
	// you'll probably want to debounce this
	$(window).resize(function() {

		// find new width
		var newWidth = body.width();

		allVideos.each(function() {

			el = $(this);

			// resize all videos according to their own aspect ratio
			el
				.width(newWidth)
				.height(newWidth * el.data('aspectRatio'));

		});

	// kick off one resize for good measure
	}).trigger('resize');

});

jquery.fluid-youtube-videos.js

// My rewritten version

$(function() {

	// Find all videos
	var $allVideos = $("iframe[src^='http://www.youtube.com']"),

	    // The thing that is fluid width
	    $fluidEl = $("body");

	// Figure out and save aspect ratio for each video
	$allVideos.each(function() {

		$(this)
			// Store aspect ratio as data
			.data('aspectRatio', this.height / this.width)
			// and remove the hard coded width/height
			.removeAttr('height')
			.removeAttr('width');

	});

	// When the window is resized
	// (You'll probably want to debounce this)
	$(window).resize(function() {

		// Find new width
		var newWidth = $fluidEl.width();

		$allVideos.each(function() {

			var $el = $(this);

			// Resize all videos according to their own aspect ratio
			$el
				.width(newWidth)
				.height(newWidth * $el.data('aspectRatio'));

		});

	// Kick off one resize for good measure
	}).resize();

});

How can you make it expand with just the parent container? Instead of to the size of the entire body?