My jailbroken Apple TV plays media files from my NAS. Together with the Airplay from other apple devices this is my home entertainment system.
But bigger files and higher bit rates caused problems. Multiple buffering and loading breaks during playback and sometimes lost connections which meant game-over back to the main menu. This vacation I would solve it.

Using Blackmagic Disk Speed Test as my testing tool, I found that the read speed over the network was very low. (first row in table below) The direct/wired connection from my router to the Apple TV (second row) was more stable but not without problems. Unfortunately the specs of the Apple TV stated an 10/100Mbit LAN connection. Nothing to gain on that route.

But wait, the Airport Express I was using only has an 100Mbit Lan connection. I replaced it with an Airport Extreme which has an 1Gbit connection. (last row) Now playback is smooth, no more buffering or endless loading.

* bigger is better, tests performed with my macbook

Be sure to measure your setup to see the affects of changes. My wired connection did not do the trick which left me puzzled. Using an 1Gbit connection upstream solved my problems.