The command-message interface is designed to be used by applications requiring a C-language interface to control multimedia devices. It uses a message-passing paradigm to communicate with MCI devices. You can send a command by using the mciSendCommand function.
The mciSendCommand function returns zero if successful. If the function fails, the low-order word of the return value contains an error code. You can pass this error code to the mciGetErrorString function to get a text description of the error.
Syntax of Command Messages
MCI command messages consist of the following 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
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.