Try please test branch of softhddevice
I have never built softhddevice before, but I hope I can get it to work.
I think I now understand your comment:
but I always thought that AMD broken vaapi in their GPU.
I have tested the brand new radeon driver 20.20 LINK
va-api does not work, not with vdr or kodi, vdpau with vdr is ok, kodi has recognized it, but do not use it.
Maybe I will test again with a fresh Ubuntu, but I don't hink it is working very well.