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_PLAY 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_OPEN command. The last parameter is the address of an MCI_PLAY_PARMS 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_MCINOTIFY message when the operation finishes.

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