The MCI_OPEN_DRIVER message requests an MCI driver to open a driver instance.
If the operation succeeds, the driver returns zero. Otherwise, the driver returns one of the MCIERR error codes defined in mmsystem.h.
A client sends the message by calling the driver’s DriverProc entry point, passing the specified parameters. When an application sends an MCI_OPEN message, winmm.dll intercepts it and sends MCI_OPEN_DRIVER to the driver.