[VDPAU] Fake VDPAU library

[Vincent Bernat]

Hi!

For platforms where a platform-specific library does not exist, does it
exist a fake library that would output nothing but that could still be
used with the tracing library? It would help testing applications using
libvdpau without having the appropriate hardware (when the rendering is
not the main point of the application to be tested).

Or maybe a VAAPI backend? The other way around exists but some
applications only support libvdpau.

Thanks.
-- 
Avoid multiple exits from loops.
            - The Elements of Programming Style (Kernighan & Plauger)