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This message requests an ACM driver to prepare the buffers associated with an ACMDRVSTREAMHEADERstructure.
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.
The ACM (Waveapi.dll) sends this message by calling the ACM driver's ACM_IOControlentry point through the DeviceIoControlfunction. 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 fdwStatusmember of 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_IOControlfunction, the ACM verifies the following conditions:
For more information about the use of this message, see the Windows NT DDK.
|Runs on||Versions||Defined in||Include||Link to|
|Windows CE OS||1.0 and later|
Note This API is part of the complete Windows CE OS package as provided by Microsoft. The functionality of a particular platform is determined by the original equipment manufacturer (OEM) and some devices may not support this API.
Last updated on Tuesday, July 13, 2004