Needless to say, this sort of mixing requires that you know what you are doing-and that you fish downloaded packages out of /var/cache/apt/archives and save them in some organized way so rollback versions can always be found. I've done this for many years now with few more issues than the ones that come up with alpha releases anyway.
I've had VDPAU support on my systems and used it on system images running on single-core machines to play 1080p video since it first became available for radeon, at first using a Red Hat package as a tarball to extract to get the necessary libraries before libg3dvl-mesa was packaged as a .deb anywhere I knew of. Worked fine all the way back to the first DRM-next kernel to support it, with just one bug then and now: 1080p AVCHD files from my camera usually play just fine, but occasionally crash the GPU so a reboot is needed to get OpenGL running again. This never happens with mp4 files containing normal H264 streams, there is something almost but not properly supported in the files my camera makes. Nvidia's blog and cards won't support those files at all, while Radeon with VDPAU plays them most of the time on every r600/Evergreen card I've tested. Normal H264 playback is fantastic, even on a 2300MHZ AMD Athlon 64 single core.