The MCIWNDM_GETLENGTH message retrieves the length of the content or file currently used by an MCI device. You can send this message explicitly or by using the MCIWndGetLength macro.
MCIWNDM_GETLENGTH
wParam = 0;
lParam = 0;
Returns the length. The units for the length depend on the current time format.
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, MCIWndGetLength