Para hacer responsive todo tipo de videos:
CSS:
.flex-video {
position: relative;
padding-top: 1.5625rem;
padding-bottom: 55.5%;
height: 0;
margin-bottom: 1rem;
overflow: hidden; }
.flex-video.widescreen {
padding-bottom: 57.25%; }
.flex-video.vimeo {
padding-top: 0; }
.flex-video iframe,
.flex-video object,
.flex-video embed,
.flex-video video {
position: absolute;
top: 0;
left: 0;
width: 100%;
height: 100%; }
HTML: (iframe, object, embed, video(html5))
<div class="flex-video">
<iframe src="http://flashservice.xvideos.com/embedframe/10572421" scrolling="no" frameborder="0" height="450" width="600"> /iframe>
</div>
<div class="flex-video">
<iframe scrolling="no" src="http://videomega.tv/cdn.php?ref=068067057048056057067051048049049048051067057056048057067068&width=700&height=430" allowfullscreen="" frameborder="0" height="430" width="700"></iframe>
</div>