Since OS X 10.9 Mavericks owners of the Apple TV have been able to wirelessly mirror their Mac screen to the big screen TV with an AirPlay feature called AirDisplay. There was just one slight problem: you couldn't stream individual videos without mirroring the whole screen.
Apple has solved this annoyance with OS X 10.11 El Capitan, which introduced richer AirPlay support permitting you to send video from Safari and other apps to the Apple TV.