index.html

<html>
<head>
  <style type="text/css">
    body {
      padding: 0;
      margin: 0;
    }
    button {
      width: 40vmin;
      height: 40vmin;
      font-size: 11vmin;
      margin: 5%;
    }
    iframe {
      width: 1px;
      height: 1px;
      top: -10px;
      position: absolute;
    }
  </style>
  <script type="text/javascript">
    var iframe;
    function play(idx) {
      iframe.src = '';
      iframe.src = '/play/' + idx;
    }
    window.onload = function() {
      iframe = document.getElementById('iframe');
      for (idx=0; idx<6; idx++) {
        var button = document.createElement('button');
        button.onclick = play.bind(window, idx);
        button.innerHTML = 'PING!';
        document.body.appendChild(button);
     }
    }
  </script>
</head>
<body>
  <iframe id="iframe" src=""></iframe>
</body></html>