youtube infinite repeater

youtube-repeat.js

(function() {
  if (!/youtube.com$/i.test(location.host)) {
    alert("hostname does not match 'youtube.com'");
    return;
  }

  var timeout;
  var resume;
  var repeat = function repeat() {
    clearTimeout(timeout);
    var play_button = document.querySelector('.ytp-button.ytp-button-play');
    // paused
    if (play_button) {
      resume = function() {
        play_button.removeEventListener('click', resume);
        setTimeout(repeat, 50);
      };
      play_button.addEventListener('click', resume);
      return;
    }

    var progress_bar = document.querySelector('.html5-progress-bar.ytp-force-transform.red');
    var replay_button = document.querySelector('.ytp-button.ytp-button-replay');
    var current = +progress_bar.getAttribute('aria-valuenow');
    var max = +progress_bar.getAttribute('aria-valuemax');
    var countdown = ((max - current) * 1000) + 50;
    if (replay_button) {
      replay_button.click();
    }
    timeout = setTimeout(repeat, countdown);
  }
  repeat();
})();

Bookmarklet: http://jsfiddle.net/lchau/55L68j45/