"I just ordered two 80mm x 80mm heat sinks and some thermal tape from amazon for very cheap. I’ll stick one to the top and bottom and hopefully that will help! Running the same test as originally, same file, same Plex app and tvOS version, etc. AppleTV is on its side, cabinet is closed up, no fan. So far it’s been running 48min and still cumulative 0 frames dropped!"
Source: Plex forum
