About IWMPPlugin
Windows Media Player calls the IWMPPlugin methods to provide the plug-in with information about the state of the connection between the plug-in and the Player. The Player calls IWMPPlugin::Init and IWMPPlugin::Shutdown to notify the plug-in about when the Player is connecting to and disconnecting from the plug-in. Rendering plug-ins also use IWMPPlugin::Init and IWMPPlugin::Shutdown to create and destroy the rendering window because these calls will always happen on the same thread. Init also provides a playback context id to allow the plug-in to determine which DirectShow graph contains it. IWMPPlugin::AdviseWMPServices and IWMPPlugin::UnAdviseWMPServices manage a pointer to IWMPServices to allow the plug-in to call methods on that interface. The Player can retrieve the class id of the plug-in by calling IWMPPlugin::GetID.