So, something very strange recently happened. I have a late 2010 Macbook Air. I was under the impression that this model was incompatible with AirPlay to an Apple TV because it didn't have the proper hardware. At some point since upgrading to El Capitan, I've now noticed that I can stream audio to my Apple TV (3rd generation) from iTunes or basically anywhere and, far more importantly, it seems like all YouTube videos now give me the option to stream to my Apple TV using AirPlay. So, this is awesome and all. But here's my question: is there any way to get this to work system wide? The AirPlay button does not show up in the menu bar. When I go in to Display, unselect the the "Show mirroring options..." box, and then reselect it, I see the AirPlay icon for all of like a half second before it displays again. Is there any way to go deep into some system files or something to get this to always display? Is there any other way to get mirroring system wide? I had long ago given up on this until suddenly AirPlay started working on YouTube. Anybody have any idea what's going on and how I can take even more advantage of this?