A source plug-in is an option available to developers who wish to implement their own storage system for Windows Media® files. A source plug-in enables this through the implementation of a COM interface called IStream, which is a standard interface for providing data.
The source plug-in should be written as a dll, and its presence is made known to the SDK through a registry entry. There can be any number of source plug-ins implemented this way. The source plug-in must export the WMCreateStreamForURL function.
To register a source plug-in, the following registry entry should be added:
Name = "any unique name"
Value = pathname of the source plug-in dll
Once the dll has been registered, the application can use the IWMReader::Open method (with the appropriate URL as a parameter) to access stream data, which can be stored in files or user-defined data containers.