Syntax of Command Messages

MCI command messages consist of the following three elements:

    A constant message value

    A structure containing parameters for the command

    A set of flags specifying options for the command and validating fields in the parameter block

The following example sends the MCI_PLAY12F75V. command to the device identified by a device identifier.

mciSendCommand(wDeviceID,            // device identifier

    MCI_PLAY,                        // command message

    0,                               // flags

    (DWORD)(LPVOID) &mciPlayParms);  // parameter block

The device identifier given in the first parameter is retrieved when the device is opened using the MCI_OPEN12F69Z1 command. The last parameter is the address of an MCI_PLAY_PARMSA2RY01 structure, which might contain information about where to begin and end playback. Many MCI command messages use a structure to contain parameters of this kind. The first member of each of these structures identifies the window that receives an MM_MCINOTIFY26GL_KY message when the operation finishes.