It appears that youtube.com can play videos over airplay somehow. With some research, it looks like it is using:
x-webkit-airplay
https://medium.com/@WebDevLiberty/push-to-airplay-button-for-html5-video-tag-ef19019eba87
It would be cool to see in caniuse.com which browsers support that. Thanks for your awesome site!