Wordpress Responsive YouTube embed

gistfile1.txt

In your themes functions.php:
add_filter( 'embed_oembed_html', 'custom_oembed_filter', 10, 4 ) ;

function custom_oembed_filter($html, $url, $attr, $post_ID) {
    $return = '<div class="video-container">'.$html.'</div>';
    return $return;
}

In your themes css:
.video-container {
    position: relative;
    padding-bottom: 56.25%;
    padding-top: 30px; height: 0; overflow: hidden;
}
 
.video-container iframe,
.video-container object,
.video-container embed {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
}