The MCIWNDM_NOTIFYMODE message notifies the parent window of an application that the operating mode of the MCI device has changed.
MCIWNDM_NOTIFYMODE 
wParam = (WPARAM) (HWND) hwnd; 
lParam = (LPARAM) (LONG) mode; 
 You can enable notification of mode changes of an MCI device by specifying the MCIWNDF_NOTIFYMODE window style.
  Windows NT: Requires version 3.1 or later.
  Windows: Requires Windows 95 or later.
  Windows CE: Unsupported.
  Header: Declared in vfw.h.
MCIWnd Window Class Overview, MCIWnd Messages