.video-wrapper {
position: relative;
padding-bottom: 56.25%;
padding-top: 25px;
height: 0;
iframe {
position: absolute;
top: 0;
left: 0;
width: 100%;
height: 100%;
}
}
<div class="video-wrapper">
<iframe width="560" height="349" src="http://www.youtube.com/embed/n_dZNLr2cME?rel=0&hd=1" frameborder="0" allowfullscreen></iframe>
</div>