This is a my fork of softhddevice plugin, which is working with vdpau (4K 8 bit output). You can use ffmpeg from 3.2x to git version.
I tested ffmpeg 3.2.10, 3.4.5, and version from git, ubuntu 18.04, Nvidia GT1030 and Radeon HD5450.
HEVC vdpau you can use with latest ffmpeg and newest video cards. Nvidia cards can works with 4xx driver, Radeon must work too.
For Nvidia with 3xx driver you can use cuvid decoder (thanks Jojo), start plugin with -w cuvid-hevc-hw-decoder or -w cuvid-hw-decoder (need make ffmpeg with cuvid decoder, not need CUDA sdk).
For oldest video cards you can disable hevc decoder with -w no-hevc-decoder.
Try who wants.