Make WordPress video embedding responsive

responsive_embed

<?php
// add these lines to your functions file
add_filter( 'embed_oembed_html', 'embed_responsively_oembed_filter', 10, 4 ) ;

// the following function will wrap the embedded code in a responsive frame, where the video is 100% width
function embed_responsively_oembed_filter($html, $url, $attr, $post_ID) {

    $return = "<style>
			.embed-container {
				position: relative;
				padding-bottom: 56.25%;
				height: 0; overflow: hidden; max-width: 100%;
			}
			.embed-container iframe,
			.embed-container object,
			.embed-container embed {
				position: absolute;
				top: 0;
				left: 0;
				width: 100%;
				height: 100%;
			}
		</style>
		<div class='embed-container'>"
			.$html.
		"</div>";
    return $return;
}