Let’s not mix things up.
I cannot comment on the remarks Bphilipson is throwing into this without further context. Reading a lot of other forum posts I tend to strongly disagree with the attitude this is just a general issue and things not getting fixed.
4K transcoding is quite demanding… even for modern systems. There’s an entire thread on the caveats and things to consider when going there.
This will highly depend on the exact details of your file. Keep in mind that hw-accelerated transcoding does not support burning in of subtitles … whenever that’s a part of the game, the heavy lifting is left to CPU. And even a gen 9 i7 can get to its limits with a complex stream.
I recommend you take a look at the 4K thread I’ve mentioned above:
As for what is/isn’t supported by GPU/CPU:
https://support.plex.tv/articles/201774043-what-kind-of-cpu-do-i-need-for-my-server/
(side note: 4K transcoding requires a PassMark score of approx. 12000 or 17000 for SDR/HDR respectively… I have not yet seen updated numbers for the newly added HDR tone mapping — I’ve found a number of gen 9 i7s that deliver a PassMark score in the area of 14-15k… that might just be not enough power)
https://support.plex.tv/articles/115002178853-using-hardware-accelerated-streaming/
