MCI_OPEN_DRIVER

dwFlags = (DWORD) lParam1; // MCI flags 
lpMCI_OPEN_PARMS = 
    (LPMCI_OPEN_PARMS) lParam2; // Pointer to MCI_OPEN_PARMS 
                                // structure.
 

This message is the version of the MCI_OPEN command sent by MCI to an MCI device.

lParam1
Contains the flags specified in the MCI_OPEN message.
lParam2
Specifies a far pointer to the MCI_OPEN_PARMS structure. This structure contains the information passed by the MCI_OPEN call from the application.

An MCI internal procedure intercepts the MCI_OPEN message sent by an application. After processing, the procedure calls the device with DRV_OPEN and MCI_OPEN_DRIVER.