OK have a strange issue...... Hardware - Livingroom AppleTV - 3rd Gen AppleTV (1080p) - v5.2.1 - Ethernet connected 100Mbit/s - Bedroom AppleTV - 3rd Gen AppleTV (1080p) - v5.2.1 - Ethernet connected 100Mbit/s - iTunes Library - Mac Mini (Mid 2001) ML 10.8.3 / iTunes 11.0.2 - Ethernet connected 100Mbit/s - Router/switch - Sky Hub SR101 - Location Livingroom Problem I have 1080p locally stored content in iTunes that plays perfectly on the Livingroom ATV. I'll supply one example file for reference. 1920x800 @ 8754kbps, low complexity, file size around 9GB. This example starts playing after about 1 - 2 seconds, and plays perfectly on the Livingroom ATV. Flicking between chapters is almost instant. If I attempt to play the same 1080p file (or any other 1080p files) on the Bedroom ATV then it sits with the spinning wheel and does nothing. I assume it would start playing eventually but i've never waited long enough to find out. SD and 720p content plays perfectly on this Bedroom ATV (see attached image). At first I though it might be a cable issue, so I tested the bandwidth across the ethernet link (using iperf) and the results are 95Mbps, so bandwidth across the ethernet link isn't a problem. I also tested the link using a different device and it was able to stream HD content no problems at all. I also tested the bandwidth on the link the Livingroom ATV uses and that also gives 95Mbps (an expected result for a 100Mbps link). Next test was to swap the ATV's location around to see if the fault followed the ATV or stayed at the location. The fault stayed at the location, so the Livingroom ATV is now in the bedroom and that ATV now can't play 1080p content from iTunes. Bedroom ATV now situated in the livingroom can play the 1080p content fine. So that would suggest a problem with the ethernet link in the bedroom, but the bandwidth tests suggest otherwise. I also connecte my MBP to the bedroom ethernet link and the same 1080p file played fine on the MBP via Quicktime. The cable run from the bedroom to the router (which is in the livingroom next to the Livingroom ATV) is around 20 meters (Cat5E cable terminated to wall sockets). So...... any thoughts?