The MCIWNDM_GETZOOM message retrieves the current zoom value used by an MCI device. You can send this message explicitly or by using the MCIWndGetZoom macro.
MCIWNDM_GETZOOM 
wParam = 0; 
lParam = 0; 
 Returns the most recent values used with MCIWNDM_SETZOOM.
A return value of 100 indicates the image is not zoomed. A value of 200 indicates the image is enlarged to twice its original size. A value of 50 indicates the image is reduced to half its original size.
  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, MCIWndGetZoom, MCIWNDM_SETZOOM