The MMSYSTEM.H file defines data types and function prototypes for all of the audio functions. You must include this header file in any source module that uses these functions. MMSYSTEM.H defines the following data types for waveform-input functions:
| Function | Description |
| HWAVEIN | A handle to an open waveform input device. |
| WAVEINCAPS | A data structure used to inquire about the capabilities of a particular waveform input device. |
| WAVEFORMAT | A data structure that specifies the data formats supported by a particular waveform input device. This data structure is also used for waveform output devices. |
| WAVEHDR | A data structure that is a header for a block of waveform input data. This data structure is also used for waveform output devices. |