.iframe-wrap {
overflow: hidden;
padding-bottom: 56.25%;
position: relative;
height: 0;
}
.iframe-wrap iframe {
left: 0;
top: 0;
height: 100%;
width: 100%;
position: absolute;
}
<div class="iframe-wrap">
<iframe width="560" height="315" src="https://www.youtube.com/embed/pEIu-WG-D-s" frameborder="0" allowfullscreen=""></iframe>
</div>