See New Features Rolling Out Soon
by 01nfinity on the Google Sites forum
1. Create a Google Slides presentation with one slide.
2. Insert > Video > "Find your video on youtube"
3. Size your video in the slide
4. Right click on the video and select "Video Options..."
5. Select "Autoplay when presenting"
6. Now go to the New Google Sites
7. Insert > Slides and select the Google slides you just created.
8. Position your slides and then click on the gear icon
9. Turn on the "Auto Start" switch.
10. Preview and enjoy!!!