Windows communicates with MCI device drivers through messages it sends to the driver. The driver processes these messages with its DriverProc entry-point function. This section contains an alphabetical list of the messages that an MCI device driver can receive. Each MCI message contains the prefix MCI_ to identify the type of the message.
A message consists of three parts: a message number, and two LPARAM parameters. Message numbers are identified by predefined message names. The two LPARAM parameters contain message-dependent values.
MCI command messages can have extensions for specific types of MCI devices.
The extensions include additional flags for parameters and are identified by one of
the following headings in the “Parameters” section of the entry for the message:
| Heading | Description |
| Animation Extensions | Extensions for animation devices |
| CD Audio Extensions | Extensions for compact disc audio devices |
| Sequencer Extensions | Extensions for MIDI sequencer devices |
| Videodisc Extensions | Extensions for videodisc player devices |
| Video Overlay Extensions | Extensions for video overlay devices |
| Wave Audio Extensions | Extensions for waveform audio devices |