ACMDM_STREAM_PREPARE (Compact 2013)

3/26/2014

This message requests an ACM driver to prepare the buffers associated with an ACMDRVSTREAMHEADER structure.

Parameters

• dwDeviceID
  Value that specifies a driver instance identifier. The driver returns this value in response to the ACM_Open (ACM Driver) function.

• hDriver
  Handle to a driver.

• uMsg
  Value that specifies this message.

• lParam1
  Pointer to an ACMDRVSTREAMINSTANCE structure.

• lParam2
  Pointer to an ACMDRVSTREAMHEADER structure.

Return Values

A return value of MMSYSERR_NOERROR indicates success. Otherwise, the driver returns one of the MMSYSERR error values declared in the Mmsystem.h header file or one of the ACMERR error values declared in the Msacm.h header file.

Remarks

The ACM (Waveapi.dll) sends this message by calling the ACM driver's ACM_IOControl entry point through the DeviceIoControl function. The ACM sends this message when an application calls acmStreamPrepareHeader. Support for this message is optional. However, if a driver supports this message, it must support ACMDM_STREAM_UNPREPARE.

If the driver returns MMSYSERR_NOTSUPPORTED, the ACM prepares the buffers for use. For most drivers, this behavior is sufficient. If the driver performs buffer preparation, it should return MMSYSERR_NOERROR. In either case, the ACM sets ACMSTREAMHEADER_STATUSF_PREPARED in the fdwStatus memberof ACMDRVSTREAMHEADER. The driver never modifies this flag. If you want both your driver and the ACM to perform buffer preparation operations, the driver should return MMSYSERR_NOTSUPPORTED after performing its preparation activity. The ACM can then perform its preparation operation.

Before calling the driver's ACM_IOControl function, the ACM verifies that the following conditions have been met:

• ACMDRVSTREAMHEADER is readable and writable.
• The cbStruct member of ACMDRVSTREAMHEADER contains a size value that is at least as large as the structure's defined size.
• The specified buffers have not already been prepared.

Requirements

Header

msacmdrv.h

See Also

Reference

ACM Driver Messages
ACM_Open (ACM Driver)
ACMDRVSTREAMINSTANCE
ACMDRVSTREAMHEADER
ACM_IOControl