WIDM_UNPREPARE

This message is used in an MMDRV_MESSAGE_PARAMS structure passed to the WAV_IOControl function to request a waveform input driver to undo the buffer preparation that was performed in response to a WIDM_PREPARE message.

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

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 WAVERR 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 user-mode drivers is optional. However, if the driver supports WIDM_PREPARE, it must support this message.

If the driver returns MMSYSERR_NOTSUPPORTED, the ACM removes the buffer preparation. For most drivers, this behavior is sufficient. If the driver supports WODM_UNPREPARE, it must clear WHDR_PREPARED in the dwFlags member of WAVEHDR and return MMSYSERR_NOERROR.