When using ATI it's a little awkward at times because the initial setup can be a little bit of trouble. The first step is to confirm the driver is working properly, and to do that you need to run this command from xorg:
if this is working it should output something similar to this: (The sample is for an old system, but current systems have similar outputs )
This should be enough to confirm that the system has OpenGL Information, however if you want to verify more in depth, use the command "glxinfo"
display: :0.0 screen: 0
OpenGL vendor string: ATI Technologies Inc.
OpenGL renderer string: Radeon X1600 Series
OpenGL version string: 2.1.7415 Release
Now the next step is easy enough... Configure everything to use OpenGL for rendering ( this should provide performance boosts).
However, the only other suggestion is to look into installing the xvba driver for vaapi.