Yeah that's on YouTube. I get why it's hard for them, as unlike in Casting, you can only deploy media types that can be natively played back in order to support Airplay, because you are passing a media reference, not a web page. But HLS is ubiquitous and Airplay supports it, so just serve the HLS and be done with it. I've been very happy with how easy it is to support this as someone who has built a number of web media apps.