[fritsch]

Success. From a short test #0321 works HW accelerated with Radeon RX 550 and AMD C-60/HD 6290. The RX 550 decodes 4k HEVC10 video as expected.

Only when playing MPEG2 SD there are many artifacts on both platforms.

 You can disable mpeg2 for VAAPI. So then post a Debug Log / screenshot?      

Log: http://ix.io/12Aq

Looks more a "feature" of the AMD drivers with low quality mpeg streams than a bug. The artifacts are there with VPAU too, but less visible: https://imgur.com/a/2nBNO 

 Yeah, sadly. bugs.freedesktop.org is then the next place.