acmStreamConvert function

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 ACMAPI 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 value

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

Return code Description
The stream header specified in pash is currently in use and cannot be reused.
The stream header specified in pash is currently not prepared by the acmStreamPrepareHeader function.
At least one flag is invalid.
The specified handle is invalid.
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 ACMSTREAMHEADERa> structure is posted back to the application's callback function with the cbDstLengthUsed member set to zero.


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

See also

Audio Compression Functions

Audio Compression Manager