start() {
    this.timer_.tickEvery(shakaDemo.Visualizer.updateFrequency_);
    this.div_.classList.remove('hidden');
    // Start out as though an automatic screenshot had been taken, so that it
    // doesn't take a screenshot during the initial buffering.
    this.autoScreenshotTaken_ = true;
  }
Starts the visualizer updating, and un-hides it.