gistfile1.html

<style>
  .video-container {
    position: relative;
    padding-bottom: 50%;
    padding-top: 30px; height: 0; overflow: hidden;
  }
   
  .video-container iframe,
  .video-container object,
  .video-container embed {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
  }
</style>

<div class="video-container">
  <iframe width="100%" height="653" src="//www.youtube.com/embed/<video_id>" frameborder="0" allowfullscreen></iframe>
</div>