It works great in MPV, I don't use VLC so I can't comment on that. The major problem right now with video acceleration is that Chromium (or maybe it's my distribution's build of it) seems to have enabled VA-API acceleration, but the Mesa VA-API state tracker (I think, I'd be glad to be corrected on this) I think is missing the API that would tell Chromium which pixel format to expect the decoder's output in; so Chromium assumes that it'll be in a certain format which it turns out not to be, and this leads to hideous corruption.

I suspect that if and when there is any significant amount of HEVC content on the web, this issue will probably be resolved by then. For now there are configuration parameters which can be used to work around the issue by disabling the pixel format Chromium defaults to, and do so just in chromium, but a fix (which will be in Mesa 19) is required for that configuration to work with Chromium (due to its unusual process naming).

I have used the MJPEG UVD decoder through ffmpeg to decode my 4K webcam's output and it works a treat.