The problem is not with you AppleTV or your Mac. Your problem is the network. I had the same problem and finally solved it.
airplay makes screen mirroring, there is a lot more data to be sent from you mac than from your iPhone or iPad
-> airplay can be okay from the small monitor, but jumpy/lag from your mac->Network handles the smaller data sufficiently enough.
"five bars on my wifi" does not mean you get great signal strength.
-->press "alt"-key on your keyboard and then click on the WiFi symbol on your mac to get more data.
You want to look at "RSSI" and "Noise".
- RSSI (=received signal strength indication) can go from 0 to -100 (on apple). Closer to 0 is better, closer to -100 is worse. My RSSI is -54dBm meaning that the signal strength is 54dBm less powerful when it reaches my mac than when it left the base station. For WiFi normal range is from -45 to -87. Below -85 is more or less unusable (for example -90 is just horrible).
- Noise is a combination of all unwanted interfering signal sources (your wifi is not the only one in the neighbourhood, radio frequencies interference etc). this is valued form 0 to -120dBm. Closer to -120 is better(little to no ninterference), closer to 0 is worse. My Noise is -94dBm.
Calculate your SNR margin by doing the following:
SNR margin = RSSI(dBm) - Noise(dBm)
for example my RSSI is -54dBm and my Noise is -94dBm and thus
my SNR margin = -54dBm - (-94dBm)= +40 --> the higher the better.
SNR over 40 excellent, 25 to 40 good, 15 to 25 airplay probably will lag, under 15 is just horrible.
What can you do to get better SNR margin which means of course no lag/jumpy video on airplay form you mac to AppleTV.
1. You can use a router that has 5Ghz instead of "the normal 2.4GHz"
-5GHz is faster with a good signal, but 2,4GHz will go through walls better. A couple of walls(even thin walls) will kill 5GHz quickly, distance also kills it more quicker than a 2,4GHz. Most people use 2.4 GHz and the channels on 2.4GHz are more crowded.
2. You can use ethernet cables to connect either your mac or your apple tv to you router. Beware there are different ethernet cables though, I tried an old ethernet cable which i got in 2000, but boy did my internet connection (internet speed test) get worse readings than through WiFi.
3. You can buy a powerline adapters (sends your network to your power line)
What did I do?
a) My router is upstairs (I get internet from 4g antenna mounted on my outer wall). ->Airplay really bad (new AppleTV 3rd gen, new 27' iMac).
b) I bought a router that handles 2.4gHz and 5Ghz (TP-Link Archer C7, cheap & got lots of awards), connected it with a new ethernetcable to my upstairs router. Connected appleTV and iMac to the new router on the 5Ghz bandwidth. -> Airplay got better but still bad.
c) put my MacBook Pro into use, pressed "alt" key and then pressed the WiFI symbol on the top right corner, looked at my RSSI and Noise and noticed that next to my apple TV my SNR margin was a lot better than next to my iMac, so the problem was the WiFi connection between my iMac to router rather than between my router and appleTV.
d) Used a longer ethernet cable so that my Archer was upstairs above the room my iMac is in-> SNR margin got better-> airplay got better ->still not watchable enough.
e) bought power line adapters (didn't know they existed, didn't believe they were good, my brother recommended them, the shop offered a 30 days trial & return policy) (Netgear powerline AV500 (XAVB5401)). Now I get internet through 4g to my original upstairs router. Upstairs router to Netgear powerline via ethernetcable. Downstairs the internet comes from my power outlet via the second Netgear powerline through ethernet cable to my Archer C7 router. iMac and appleTv are connected to Archer-router via 5Ghz WiFi. ->Airplay works wonderfully with VLC,iDVD,Quicktime,iTunes, from a movie DVD connected to my iMac.
One could of course just use router to powerline via ethernet cable and then powerline to mac and another poweline to appleTv that would have been the neater solution.
You can also look what channels your neighbors use (press "alt"-key + click on WiFI symbol). there are some charts in the net that show what channels interfere , what channel should you put your router on.
An easy test should be to put your router, computer and Apple TV next to each others and try airplay (hey your router doesn't have to be connected to the internet to be able to do this), if that solves the lag, then your network is definately the problem (SNR margin remember?).
Hope this helped, i cursed that I didn't find an explanation like this, people just say "bad apple", "why doesn't apple fix this", "I have 5 bars on my Wifi so the network can not be my problem" "solved it by lowering my resolution (=less data to be send so they had almost enough of SNR margin, enough for low resolution(less data), not enough for higher resolution or something like that)! !
Click "this helped me" if this really helped, you so more people find this lengthy text easier ! !