[DJ_Izumi]

To my knowledge R9 390X has UVD 6 that does support hevc.

Also possible that LAVFilters, which is used by MPC-HC, adds some additional capabilities.

You're wrong about the 390X but so was I when I bought it. The 390 and 390X has UVD 4.2 as it's a GCN 1.1 chip. However the 380, 380X, have UVD 5.0 via their GCN 1.2 architecture and the Nano/Fury and beyond have UVD 6 also with GCN 1.2 architecture. So my 390X can't do anything beyond 4K H264. Yeah, the 390 and 390X have the crappiest secondary features, almost funny except that it's not.

Looking closely at MPC, it's using it's own software decoder, which is FFMPEG that it's built on, I even set the renderer to the old one that doesn't even support DXVA, and the 4930K is still spitting out buttery smooth 4K HEVC 60fps and 'Sofware Decoding' is what it's status screen is reporting. I'm pretty certain that MPC-HC is not doing any form of hybrid decoding and this system has no DXVA support for HEVC in it for any software to accidently use.

So why does Kodi seem to have a heart attack on the same files when the decoding core of both pieces of software are built around the same open source project. This isn't a small variation, this is 40% CPU usage full frame rate vs 100% CPU usage and 2/3rd frame rate. That difference is MASSIVE.

Using VLC, which is purely self-contained and again uses FFMPEG I get the same approximate results as MPC-HC gets.

So... Why?

Why does Kodi seem to be massively inefficient at this in comparison to something else using FFMPEG?