Responsive video's

gistfile1.phtml

<?php 
function mytheme_wrap_oembed_with_div( $html ) {
     return '<div class="oembed-container">' . $html . '</div>';
}
add_filter( 'embed_oembed_html', 'mytheme_wrap_oembed_with_div', 10, 3);
add_filter( 'video_embed_html', 'mytheme_wrap_oembed_with_div' );
?>

.oembed-container {
	display: block;
	max-width: 100%;
	margin-bottom: 0.75em;
}
.oembed-container embed,
.oembed-container iframe,
.oembed-container object,
.oembed-container video {
          position: absolute;
          top: 0;
          left: 0;
          width: 100%;
          height: 100%;
}
.oembed-container {
          position: relative;
          padding-bottom: 56.25%;
          height: 0;
          overflow: hidden;
}