Each message received by the widMessage function comes with two DWORD parameters. For some messages, one of these parameters points to a data structure containing additional information from the client, or to an empty data structure for the driver to fill with information for the client.
Waveform input device drivers use the data structures listed in the following table. See “Audio Device Driver Reference,” later in this chapter, for details on these data structures.
A client-filled structure providing specific information about the format for PCM waveform data.
A client-filled structure providing general information about the format of waveform data.
A client-filled structure identifying a waveform data block.
A client-filled structure providing information about opening a waveform device.
A driver-filled structure providing a client with information about the capabilities of a waveform input device.
With the exception of WAVEINCAPS, these are the same data structures used by waveform output drivers.