The MMSYSTEM.H header file defines data types and function prototypes for MCI. You must include this header file in any source module that uses MCI functions.
The following list contains data types for parameter blocks used with extended MCI commands related to audio. For a complete list of all MCI data types, see the chapter on data types in the Multimedia Programmer's Reference.
| Type | Description |
| MCI_SEQ_SET_PARMS | ||
| A data structure for specifying a parameter block for the MCI_SET command for MIDI sequencer devices. | ||
| MCI_WAVE_OPEN_PARMS | ||
| A data structure for specifying a parameter block for the MCI_OPEN command for waveform audio devices. | ||
| MCI_WAVE_SET_PARMS | ||
| A data structure for specifying a parameter block for the MCI_SET command for waveform audio devices. | ||