The MMSYSTEM.H file defines data types and function prototypes for all of the low-level audio functions. MMSYSTEM.H defines the following data types for low-level MIDI input functions:
HMIDIIN
A handle to a MIDI input device.
MIDIHDR
A data structure that is a header for a block of MIDI system-exclusive data. This data structure is used for input as well as output.
MIDIINCAPS
A data structure used to inquire about the capabilities of a MIDI input device.