Facebook’s new music service actually knows when Spotify is playing a song in your browser:

Was kinda curious as to why this worked. It was very responsive and didn’t seem to be using a uri scheme. So I investigated some:

Looks like Facebook is actually polling for a server on the local machine listening on a particular port to control it. This really makes me want to instigate web sockets more.

EDIT:

Looking into it some more you can see it’s just a json get request. Not necessarily a web socket connection: