Re: VDPAU and studio levels (16-235) possible?
The standard (default) CSC matrices provided by VDPAU (as part of VdpVideoMixerRender) do convert the video to PC pixel value ranges. You can either use brightness/contrast controls (as you have done) to adjust the CSC matrix, or explicitly provide your own CSC matrix (which would be a good option for an app to have; either explicit TV level option, or custom CSC option). With the appropriate brightness/contrast values, or custom CSC matrix, this should create no loss of original video pixel values.
Hope this helps.