Make iframes responsive by calculating the correct aspect ratio and filling to the width of the container as it flexes.

responsive-iframes.js

// iframes
var  $iframes = $( document.querySelectorAll( '.videos iframe' ) );

function iframeSizing() {
	var	$this			= $( this ),
		width			= $this.width(),
		height			= $this.height(),
		containerWidth		= $this.parent().width(),
		heightRatio		= height / width,
		newHeight		= heightRatio * containerWidth;

	$this.width( containerWidth );
	$this.height( newHeight );
}

function iframesEachSizing() {
	$iframes.each( iframeSizing );
}

iframesEachSizing();

$( window ).resize( iframesEachSizing );