Viewport Height YouTube

The widget displays a viewport height poster image on page load so that the video file doesn't have to download until played.
The video player is responsive rather than viewport size. It is centered horizontally and vertically inside the viewport height container. Play the video and adjust the browser width and height to see how it reacts to these changes.
Autoplay
Autoplay should only be used if the video is the first item on the page and the page will not be available to mobile phone users.