acmStreamUnprepareHeader function (msacm.h)

Article
06/24/2021

The acmStreamUnprepareHeader function cleans up the preparation performed by the acmStreamPrepareHeader function for an ACM stream. This function must be called after the ACM is finished with the given buffers. An application must call this function before freeing the source and destination buffers.

Syntax

MMRESULT ACMAPI acmStreamUnprepareHeader(
  HACMSTREAM        has,
  LPACMSTREAMHEADER pash,
  DWORD             fdwUnprepare
);

Parameters

has

Handle to the conversion steam.

pash

Pointer to an ACMSTREAMHEADER structure that identifies the source and destination buffers to be unprepared.

fdwUnprepare

Reserved; must be zero.

Return value

Returns zero if successful or an error otherwise. Possible error values include the following.

Return code	Description
ACMERR_BUSY	The stream header specified in pash is currently in use and cannot be unprepared.
ACMERR_UNPREPARED	The stream header specified in pash is currently not prepared by the acmStreamPrepareHeader function.
MMSYSERR_INVALFLAG	At least one flag is invalid.
MMSYSERR_INVALHANDLE	The specified handle is invalid.
MMSYSERR_INVALPARAM	At least one parameter is invalid.

Remarks

Unpreparing a stream header that has already been unprepared is an error. An application must specify the source and destination buffer lengths (cbSrcLength and cbDstLength, respectively) that were used during a call to the corresponding acmStreamPrepareHeader. Failing to reset these member values will cause acmStreamUnprepareHeader to fail with an MMSYSERR_INVALPARAM error.

The ACM can recover from some errors. The ACM will return a nonzero error, yet the stream header will be properly unprepared. To determine whether the stream header was actually unprepared, an application can examine the ACMSTREAMHEADER_STATUSF_PREPARED flag. If acmStreamUnprepareHeader returns success, the header will always be unprepared.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Target Platform	Windows
Header	msacm.h
Library	Msacm32.lib
DLL	Msacm32.dll