VRAM capture property issue in avstream driver(for camera)


I have been trying to expose the VRAM property set -> KSPROPSETID_VramCapture, in my avstream minidriver for camera. And I am using media foundation as the framework.

I am modifying the sample avstream driver provided by microsoft which is - “avshws” (http://code.msdn.microsoft.com/windowshardware/AVSHwS-AVStream-Simulated-7953991d).

I have exposed all the properties within this set.

According to documentation given by microsoft on this page -> http://msdn.microsoft.com/en-us/library/windows/hardware/ff568780(v=vs.85).aspx, KSPROPERTY_PREFERRED_CAPTURE_SURFACE get property request should be received. But, what I have observed is that, instead of the above step taking place, KSPROPERTY_CURRENT_CAPTURE_SURFACE set property request with KS_CAPTURE_ALLOC_SYSTEM as its value. So, I return STATUS_UNSUCCESSFUL as HRESULT for the set request, but still I am unable to get a KSPROPERTY_PREFERRED_CAPTURE_SURFACE get property request.

Can anyone tell me what could be the possible reason for this anomaly?