Even with the following extraPackages, VDPAU was not working:
# VDPAU driver with OpenGL/VAAPI backend
pkgs.libvdpau-va-gl
# VDPAU driver for the VAAPI library
pkgs.vaapiVdpau
According to the Arch wiki, VDPAU might need configuration [3]. This did the trick for me:
env VDPAU_DRIVER=radeonsi nix-shell -p vdpauinfo --run vdpauinfo
display: :0 screen: 0
API version: 1
Information string: G3DVL VDPAU Driver Shared Library version 1.0
Video surface:
name width height types
-------------------------------------------
420 16384 16384 NV12 YV12
...
Edit: I just confirmed that VDPAU still works without (redundantly) providing those extraPackages. The only thing that is missing is the environment variable VDPAU_DRIVER with the correct driver in use.
This seems to be an older issue, see e.g. Vdpau through vaapi - #2 by ony