Source code and descriptions of two sample AVStream minidrivers are provided in the MSDN Code Gallery:
AVStream Filter-Centric Simulated Capture Driver (Avssamp)
A pin-centric capture driver for a simulated piece of hardware that shows how to implement DMA through AVStream.
AVStream Simulated Hardware Sample Driver (AVSHwS)
A filter-centric capture driver that does not perform direct memory access (DMA).
These samples demonstrate many of the concepts that are described in this documentation, and the samples can be tailored to a driver developer's needs.