<!DOCTYPE html>
<html>
<head>
  <title>Progressive Demo</title>
  <style>
    body {
      background-color: rgb(255, 255, 255);
      color: #0047ab;
      font-size: 100px;
    }
    .small {
      margin: 100px;
      border: 10px solid blue;
      width: 960px;
      height: 540px;
    }
    .big {
      margin: 10px;
      border: 10px solid blue;
      width: 1280px;
      height: 720px;
    }
  </style>
</head>
<body>
  <div>Progressive Demo</div>
  <video autoplay loop id="v" class="small" src="progressive.mp4"></video>
  <script>
    window.setInterval(function() {
      if (document.getElementById('v').className === 'big')
        document.getElementById('v').className = 'small';
      else
        document.getElementById('v').className = 'big';
    }, 3000);
  </script>
</body>
</html>