Responsive video. Blog post: http://www.miguelmota.com/blog/responsive-video

responsive-video.js

(function() {
  // Responsive Video
  function responsiveVideo(selector) {
    // Get videos
    var videos = document.querySelectorAll(selector);

    // Loop through videos
    for (var i = 0; i < videos.length; i++) {
      var video = videos[i];

      // Get aspect ratio
      var videoRatio = (video.height / video.width) * 100;

      // Stretch video
      video.style.position = 'absolute';
      video.style.top = 0;
      video.style.left = 0;
      video.setAttribute('width','100%');
      video.setAttribute('height','100%');

      // Add a wrapper to contain video
      var wrapper = document.createElement('div');
      wrapper.className = 'video-wrap';
      wrapper.style.width = '100%';
      wrapper.style.position = 'relative';
      wrapper.style.paddingTop = videoRatio + '%';

      // Add it to the DOM
      var parentNode = video.parentNode;
      parentNode.insertBefore(wrapper, video);
      wrapper.appendChild(video);
    }
  }

  // Initialize. Make sure it's after DOMContentLoaded.
  responsiveVideo('.video');
})();