<!DOCTYPE HTML>
<html>
<head>
  <meta http-equiv="content-type" content="text/html; charset=utf-8" />
  <script type="text/javascript" charset="utf-8" src="dist/clappr.min.js"></script>
  <script type="text/javascript" charset="utf-8" src="dist/playbackname.js"></script>
  <title>clappr-playback-name-plugin Test Page</title>
  <script type="text/javascript" charset="utf-8">
window.onload = function() {
  var player = new Clappr.Player({
    sources: ['http://www.html5rocks.com/en/tutorials/video/basics/devstories.mp4'],
    plugins: {
      container: [PlaybackName]
    },
    width: 640, height: 360,
  });
  player.attachTo(document.getElementById('player-wrapper'));
}
  </script>
</head>
<body>
  <div align="center">
    <div id="player-wrapper">
  </div>
  </div>
</body>
</html>


<!DOCTYPE HTML>
<html>
<head>
  <meta http-equiv="content-type" content="text/html; charset=utf-8" />
  <script type="text/javascript" charset="utf-8" src="dist/clappr.min.js"></script>
  <script type="text/javascript" charset="utf-8" src="dist/playbackname.js"></script>
  <title>clappr-playback-name-plugin Test Page</title>
  <script type="text/javascript" charset="utf-8">
window.addEventListener('DOMContentLoaded', function() {
  var player = new Clappr.Player({
    sources: ['http://www.html5rocks.com/en/tutorials/video/basics/devstories.mp4'],
    plugins: {
      container: [PlaybackName]
    },
    width: 640, height: 360,
  });
  player.attachTo(document.getElementById('player-wrapper'));
});
  </script>
</head>
<body>
  <div align="center">
    <div id="player-wrapper">
  </div>
  </div>
</body>
</html>


Use DOMContentLoaded to instantiate player
Use DOMContentLoaded to instantiate player

Listen to `DOMContentLoaded` instead of overwriting `window.onload` handler.