It just doesn't work and returns random chunks of video memory!? (scary!) Many, many hours wasted on this. It seems that for whatever reason, it just cannot be made to work.
r5683 tries to avoid using the nvidia
OpenCL implementation. It is unfortunate since RGB to YUV does work and could be used server-side... but at initialisation time, we don't know which is going to get used.
Enough time wasted already, I'm not going to fix this.
csc opencl has been removed in 2.0
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/525