x265 is not using HW for decoding so it's very heavy on the CPU.
Please don't confuse "x265" and "H.265 / HEVC"
At least on paper, some hardware h.265 decoding is supported on Intel since Haswell (2013), on nVidia since Maxwell 2-nd gen (2015), on AMD since Polaris (2016).
Is it possible to (ab)use that hardware support to do other tasks by mapping them to a decoding task?
Dunno. Why would you want to? You can already compute lots of stuff on GPUs.
Couple generations ago, AMD did the other way, they used GPU shader ALUs for video encoding/decoding. They stopped doing that because power efficiency is worse than custom silicon that’s now in all modern GPUs, even in mobile SoCs.
However, it doesn't handle X.265 videos very well - pauses every few frames.
How come? I'm assuming its because 265 is much more CPU intensive.
What's the typical compression benefit of using x.265 vs x.264?
-----------------------------------
Update: noticed this comment below from @Causality1 "devices from over a decade ago have hardware h264 decoders. Extremely low powered modern devices can play very large 265 videos, if they have a hardware decoder."