I now have my a UHD video (from the one UHD 4K disc I own) and also the HD version. Impressively, Emby Theater on Windows 10 plays the UHD video pretty well. Audio and Video in my brief check played without stuttering or losing sync. That's cool and unexpected for me.
But I noticed on a scene with large white region (the Hockey rink in Deadpool, about 1:02:00 (hh:mm:ss) in) there was large macro-blocking visible. It's not there in the HD version, so it's from the on-the-fly conversion of 4K down to HD.
What, if anything, can I tweak in Emby Theater or Server to get better playback of 4K material on my 2K system? It would be a bonus if I could start collecting 4K media and only have to keep the 4K file saved, trusting Emby to play it perfectly on my HD system. That might be not practical, but it's worth a check.
My Emby Server (and playback PC) is a 6th Gen Core i5-6500 with Intel HD Graphics 530 (integrated graphics).
Thanks for any insights into how UHD is played back at HD from Emby and tips to improve that performance!