Has anyone actually managed to get some sort of xvmc working with xvba (Radeon HD with UVD2)?

It seems to be required to use XvMCW as wrapper because we don't have any header files for xvba available, but even with XvMCW installed (and /etc/X11/XvMCConfig in place) I can't get mplayer or xine working.

xvmcinfo reports:
Xv version 2.2
XvMC version 1.1

screen number 0
info for adaptor 0 [ATI Radeon AVIVO Video]
number of XvMC surface types: 1

info about surface 0:
max_width=1920
max_height=1080
subpicture_max_width=1920
subpicture_max_height=1080
chroma_format:
XVMC_CHROMA_FORMAT_420
mc_type:
format : MPEG2
accelaration start from : IDCT
flags:
XVMC_BACKEND_SUBPICTURE
But mplayer ist just outputting garbage (green and pink dots) while xine is even segfaulting.

This is on a Gentoo x86_64 system using a Radeon HD 4870 with Catalyst 9.5


Thanks for any hints!