Since Youtube changed embeded videos to only be able to be played in an iframe or by using their API, not put directly in a browser window, you must now implement Youtube with an iframe. Howerver, you cannot let videos played automatically unmuted. Only muted. This is due to restrictions of the browser engine. But you can turn this feature off and allow autoplay with sound. It is a flag. SL should run the internal browser with this flag so you can create TVs again which autoplay youtube videos with sound.