function sync() {
    /*
    Gets all of the playback speed classes.
    */
    var playbackSpeedClasses = document.getElementsByClassName("amplitude-playback-speed");

    /*
    Iterates over all of the playback speed classes
    applying the right speed class for visual purposes.
    */
    for (var i = 0; i < playbackSpeedClasses.length; i++) {
      /*
      Removes all of the old playback speed classes.
      */
      playbackSpeedClasses[i].classList.remove("amplitude-playback-speed-10");
      playbackSpeedClasses[i].classList.remove("amplitude-playback-speed-15");
      playbackSpeedClasses[i].classList.remove("amplitude-playback-speed-20");

      /*
      Switch the current playback speed and apply the appropriate
      speed class.
      */
      switch (_config2.default.playback_speed) {
        case 1:
          playbackSpeedClasses[i].classList.add("amplitude-playback-speed-10");
          break;
        case 1.5:
          playbackSpeedClasses[i].classList.add("amplitude-playback-speed-15");
          break;
        case 2:
          playbackSpeedClasses[i].classList.add("amplitude-playback-speed-20");
          break;
      }
    }
  }
Sets all of the visual playback speed buttons to have the right class
to display the background image that represents the current playback
speed.

@access public