The acmStreamConvert function requests the ACM to perform a conversion on the specified conversion stream. A conversion may be synchronous or asynchronous, depending on how the stream was opened.

MMRESULT acmStreamConvert(
  HACMSTREAM has,          
  DWORD fdwConvert         



Handle to the open conversion stream.


Pointer to a stream header that describes source and destination buffers for a conversion. This header must have been prepared previously by using the acmStreamPrepareHeader function.


Flags for doing the conversion. The following values are defined.

Value Meaning
ACM_STREAMCONVERTF_BLOCKALIGN Only integral numbers of blocks will be converted. Converted data will end on block-aligned boundaries. An application should use this flag for all conversions on a stream until there is not enough source data to convert to a block-aligned destination. In this case, the last conversion should be specified without this flag.
ACM_STREAMCONVERTF_END ACM conversion stream should begin returning pending instance data. For example, if a conversion stream holds instance data, such as the end of an echo filter operation, this flag will cause the stream to start returning this remaining data with optional source data. This flag can be specified with the ACM_STREAMCONVERTF_START flag.
ACM_STREAMCONVERTF_START ACM conversion stream should reinitialize its instance data. For example, if a conversion stream holds instance data, such as delta or predictor information, this flag will restore the stream to starting defaults. This flag can be specified with the ACM_STREAMCONVERTF_END flag.

Return Values

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

Value Description
ACMERR_BUSY The stream header specified in pash is currently in use and cannot be reused.
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.


You must use the acmStreamPrepareHeader function to prepare the source and destination buffers before they are passed to acmStreamConvert.

If an asynchronous conversion request is successfully queued by the ACM or driver and the conversion is later determined to be impossible, the ACMSTREAMHEADER structure is posted back to the application's callback function with the cbDstLengthUsed member set to zero.


  Windows NT/2000/XP: Included in Windows NT 3.1 and later.
  Windows 95/98/Me: Included in Windows 95 and later.
  Header: Declared in Msacm.h.
  Library: Use Msacm32.lib.

See Also

Audio Compression Manager, Audio Compression Functions, acmStreamPrepareHeader, ACMSTREAMHEADER