The MCIWNDM_NOTIFYMEDIA message notifies the parent window of an application that the media has changed.
MCIWNDM_NOTIFYMEDIA
wParam = (WPARAM) (HWND) hwnd;
lParam = (LPARAM) (LPSTR) lp;
You can enable notification of media changes by specifying the MCIWNDF_NOTIFYMEDIA 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