TPositionEvent = procedure ( Sender: TObject; Index: Longint ) of
object;
property OnPosition: TPositionEvent;
OnPosition occurs when the play position reaches an offset specified in one of the positions defined through the SetNotificationPositions method. The Index identifies the array's notification position that triggered this event.
To use notify on playback buffers, specify the DSBCAPS_CTRLPOSITIONNOTIFY flag on buffer creation.