WIDM_PREPARE

This message is used in an MMDRV_MESSAGE_PARAMS structure passed to the WAV_IOControl function to request a waveform input driver to prepare a system-exclusive data buffer for input.

Parameters

uDeviceId

Device identifier—0, 1, 2, and so on—for the target device.

uMsg

Specifies this message.

dwUser

Specifies a device instance identifier.

dwParam1

Specifies a pointer to a WAVEHDR structure identifying the buffer.

dwParam2

Specifies the size, in bytes, of WAVEHDR.

Return Values

MMSYSERR_NOERROR indicates success. Otherwise, the driver returns one of the MMSYSERR or WAVEERR error values declared in the Mmsystem.h header file.

Remarks

The ACM sends this message by calling the audio driver’s WAV_IOControl entry point through the DeviceIoControl function.

Support for this message by drivers is optional. However, if the driver supports this message, it must support WIDM_UNPREPARE.

If the driver returns MMSYSERR_NOTSUPPORTED, Waveapi.dll prepares the buffer for use. For most drivers, this behavior is sufficient. If the driver performs buffer preparation, it must set WHDR_PREPARED in the dwFlags member of WAVEHDR and return MMSYSERR_NOERROR.