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Initializing an AVStream Minidriver

An AVStream minidriver that does not handle device initialization on its own calls KsInitializeDriver from the minidriver's DriverEntry routine. KsInitializeDriver initializes the driver object of an AVStream driver, in addition to IRP dispatching, PnP add device messages, and unloading.

In calling KsInitializeDriver, the minidriver passes a pointer to the driver object to initialize a pointer to the registry path, and optionally, a device descriptor object. Note that passing the KSDEVICE_DESCRIPTOR object is not required. If the minidriver does pass a device descriptor, AVStream creates a device with the specified characteristics at AddDevice time.

The device descriptor object contains a pointer to a KSDEVICE_DISPATCH structure as well as an array of filter descriptors. Provide a KSFILTER_DESCRIPTOR for each filter type that your minidriver supports. When the minidriver calls KsInitializeDriver, AVStream creates a filter factory object for each type of filter exposed by the minidriver. Individual filters are then instantiated by the filter factory upon receipt of a create IRP for the associated create item. Each filter descriptor contains a pointer to an array of KSPIN_DESCRIPTOR_EX objects. AVStream creates a pin factory on the relevant filter for each type of pin the minidriver exposes through that filter.

When a connection is made to a given pin type on a filter, the AVStream pin factory creates a pin object. Note that each filter must expose at least one pin. The minidriver uses the InstancesNecessary member of KSPIN_DESCRIPTOR_EX to identify the number of instances of this pin type that are necessary for the filter to function correctly. Similarly, the minidriver can impose a maximum on the number of pins that the pin factory can instantiate by using the InstancesPossible member of this structure.

AVStream supports two types of processing: filter-centric processing, and pin-centric processing. When laying out the descriptors, decide which type of processing each filter type will perform.

Installing an AVStream Minidriver

An AVStream minidriver must have an INF file that the system uses to install the driver. An AVStream INF file is based on the common INF format, which is described in Creating an INF File. You can also refer to the INF files supplied with AVStream sample drivers in the Windows Driver Kit (WDK). Keep in mind the following AVStream-specific guidelines.

If you are writing a minidriver for a parent device, the AddReg section of your INF file should contain:


If you are writing a minidriver for a child device, the AddReg section should contain:


Note that "AVStream" would be "Stream" for a stream class driver.

For all AVStream minidrivers, the filter-specific reference string in the INF file must match the ReferenceGuid member of the KSFILTER_DESCRIPTOR structure.

For more information about descriptors, see AVStream Descriptors.



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