Wordpress: responsive oembeds - youtube, vimeo, images, etc

functions-oembed.php

/*
  Creates a container around embeds
 */
function responsive_embed_wrapper($content) {
  return '<figure class="oembed-wrap">' . $content . '</figure>';
}
add_filter('embed_oembed_html', 'responsive_embed_wrapper', 10, 3);

styles-oembed.css

/* oembed container */
.oembed-wrap{
  height: 0;
  margin-bottom: 1.35em;
  margin-top: 1.35em;
  padding-bottom: 56.25%;
  position: relative;
  overflow: hidden;
}
.oembed-wrap iframe,
.oembed-wrap object,
.oembed-wrap embed,
.oembed-wrap video{
  height: 100%;
  left: 0;
  position: absolute;
  top: 0;
  width: 100%;
}