Purchased Mac (Retina 5K, 27-inch, Late 2015) July 2nd and decided to try the High Sierra Beta. Has been an eye opening experience. Dutifully complete Feedback when issues occur, and fortunately haven't developed any of the major issues I've seen other experience on the forums. Have been trying to get my Apple TV to mirror from the mac, without success. Have gone online and reviewed all the steps that I've found to no avail. I feel it is something to do dierctly with the Mac, as I have 4 different iphones and an Ipad in the home and all work, immediately. Using the Systems Preferences, I go into Display optins and toggle the AirPlay Display to Apple TV and almost immediately get the message as above, with "Apple TV" being the name of my Apple TV. It's as though the mac can't send any signal out to even look for it. Clicking on the icon at the top of the screen you can see the greyed out area 'air play: looking for Apple TV' and then changing to 'Air Play: Off'. Wondering if anyone else having the same problems. As I mentioned, I've done everything to rectify the problem that I could find online. Power cycle, check for same network (both are on ethernet, and I've tried Wi-Fi), Firewall...the list goes on. Any help or other ideas would be appreciated. 2nd gen Apple TV, up to date software.
Could not connect to "Apple TV"
May be a problem, with ATV Gen.2, and downscaling your Screen from 5K to 720p.
The 2.gen, only give HDReady, FullHD are possible on Gen3 and 4.
You should try with ATV Gen 3 or 4.
I assume, that High Sierra uses Airplay 2. This is not compatible with ATV 2.Gen. It will also not work with IOS 11 Beta, which I tested.
I hope, that Apple will bring an update for ATV 2nd Gen. to support Airplay 2.
I have this problem with a 2017 MacBook Pro and a gen 3 ATV.
My 'Could no connect to "Apple TV"' message comes up after about 3 seconds of ostensibly trying to connect to the ATV whether it is turned on or left off: it never turns on when I am trying to connect, only if I use the ATV remote.