The engine object receives notifications from the audio-destination object about the status of audio being played, such as whether the audio-destination object has space available for more text.
The engine object can notify the application about events that pertain to text-to-speech, such the time that audio starts or stops playing. To receive notifications, the application calls the ITTSCentral::Register member function on the engine object and passes the address of the notification interface. The application must create a COM object that supports the ITTSNotifySink interface. The application developer determines how the application responds to notifications.