The IUnknown interface is the OLE interface from which AVIFile and AVIStream interfaces are derived. Interfaces used with AVI files rely on definitions of the QueryInterface, AddRef, and Release methods from this interface.
Windows NT: Requires version 3.1 or later.
Windows: Requires Windows 95 or later.
Windows CE: Unsupported.
Header: Declared in unknwn.h.
Custom File and Stream Handlers Overview, Custom File and Stream Handler Interfaces