Yea but if someone sends me a link to one to look at later, I still don’t want it to start autoplaying in class.

Maybe have an obvious ?autoplay=true param.

I don't disagree with you, but I personally think it's a poor design choice. Why not let the user decide which content to watch?

If twitch offers an option for sound on embedded videos to be muted, that would be perfect -- at least on the home page where people who are checking out a site for the first time are most likely to land, getting blasted by unexpected sound is annoying.