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ACMSTREAMHEADER structure (msacm.h)

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The ACMSTREAMHEADER structure defines the header used to identify an ACM conversion source and destination buffer pair for a conversion stream.

Syntax

typedef struct tACMSTREAMHEADER {
  DWORD     cbStruct;
  DWORD     fdwStatus;
  DWORD_PTR dwUser;
  LPBYTE    pbSrc;
  DWORD     cbSrcLength;
  DWORD     cbSrcLengthUsed;
  DWORD_PTR dwSrcUser;
  LPBYTE    pbDst;
  DWORD     cbDstLength;
  DWORD     cbDstLengthUsed;
  DWORD_PTR dwDstUser;
  DWORD     dwReservedDriver[_DRVRESERVED];
} ACMSTREAMHEADER, *PACMSTREAMHEADER, *LPACMSTREAMHEADER;

Members

cbStruct

Size, in bytes, of the ACMSTREAMHEADER structure. This member must be initialized before the application calls any ACM stream functions using this structure. The size specified in this member must be large enough to contain the base ACMSTREAMHEADER structure.

fdwStatus

Flags giving information about the conversion buffers. This member must be initialized to zero before the application calls the acmStreamPrepareHeader function and should not be modified by the application while the stream header remains prepared.

Name Description
ACMSTREAMHEADER_STATUSF_DONE
 Set by the ACM or driver to indicate that it is finished with the conversion and is returning the buffers to the application.
ACMSTREAMHEADER_STATUSF_INQUEUE
 Set by the ACM or driver to indicate that the buffers are queued for conversion.
ACMSTREAMHEADER_STATUSF_PREPARED
 Set by the ACM to indicate that the buffers have been prepared by using the acmStreamPrepareHeader function.

dwUser

User data. This can be any instance data specified by the application.

pbSrc

Pointer to the source buffer. This pointer must always refer to the same location while the stream header remains prepared. If an application needs to change the source location, it must unprepare the header and reprepare it with the alternate location.

cbSrcLength

Length, in bytes, of the source buffer pointed to by pbSrc. When the header is prepared, this member must specify the maximum size that will be used in the source buffer. Conversions can be performed on source lengths less than or equal to the original prepared size. However, this member must be reset to the original size when an application unprepares the header.

cbSrcLengthUsed

Amount of data, in bytes, used for the conversion. This member is not valid until the conversion is complete. This value can be less than or equal to cbSrcLength. An application must use the cbSrcLengthUsed member when advancing to the next piece of source data for the conversion stream.

dwSrcUser

User data. This can be any instance data specified by the application.

pbDst

Pointer to the destination buffer. This pointer must always refer to the same location while the stream header remains prepared. If an application needs to change the destination location, it must unprepare the header and reprepare it with the alternate location.

cbDstLength

Length, in bytes, of the destination buffer pointed to by pbDst. When the header is prepared, this member must specify the maximum size that will be used in the destination buffer.

cbDstLengthUsed

Amount of data, in bytes, returned by a conversion. This member is not valid until the conversion is complete. This value can be less than or equal to cbDstLength. An application must use the cbDstLengthUsed member when advancing to the next destination location for the conversion stream.

dwDstUser

User data. This can be any instance data specified by the application.

dwReservedDriver[_DRVRESERVED]

Reserved; do not use. This member requires no initialization by the application and should never be modified while the header remains prepared.

Remarks

Before an ACMSTREAMHEADER structure can be used for a conversion, it must be prepared by using the acmStreamPrepareHeader function. When an application is finished with an ACMSTREAMHEADER structure, it must call the acmStreamUnprepareHeader function before freeing the source and destination buffers.

Requirements

Requirement Value
Minimum supported client Windows 2000 Professional [desktop apps only]
Minimum supported server Windows 2000 Server [desktop apps only]
Header msacm.h

See also

Audio Compression Manager

Audio Compression Structures

acmStreamPrepareHeader

acmStreamUnprepareHeader