onYTReady() {
    this.videos.forEach(video => {
      const player = new Player(video);

      if (typeof video.dataset.autoplay !== 'undefined') {
        const {i} = Slide.getSectionFromEl(player.el);
        const slide = this.ws_.slides[i - 1];

        slide.player = player;

        slide.el.addEventListener(SlideEvents.ENABLE, YouTube.onSlideEvent);
        slide.el.addEventListener(SlideEvents.DISABLE, YouTube.onSlideEvent);
        slide.el.addEventListener(SlideEvents.ENTER, YouTube.onSlideEvent);
        slide.el.addEventListener(SlideEvents.LEAVE, YouTube.onSlideEvent);

        if (this.ws_.currentSlide_ === slide) {
          YouTube.onSectionEnabled(slide);
        }
      }
    });
  }
Once the YouTube API is ready this gets called so we can start the videos.