The acmFilterEnum function enumerates waveform-audio filters available for a given filter tag from an ACM driver. This function continues enumerating until there are no more suitable filters for the filter tag or the callback function returns FALSE.

MMRESULT acmFilterEnum(
  HACMDRIVER         had,        
  ACMFILTERENUMCB    fnCallback, 
  DWORD_PTR          dwInstance, 
  DWORD              fdwEnum     



Handle to the ACM driver to query for waveform-audio filter details. If this parameter is NULL, the ACM uses the details from the first suitable ACM driver.


Pointer to the ACMFILTERDETAILS structure that contains the filter details when it is passed to the function specified by fnCallback. When your application calls acmFilterEnum, the cbStruct, pwfltr, and cbwfltr members of this structure must be initialized. The dwFilterTag member must also be initialized to either WAVE_FILTER_UNKNOWN or a valid filter tag.


Procedure-instance address of the application-defined callback function.


A 32-bit (DWORD), 64-bit (DWORD_PTR) application-defined value that is passed to the callback function along with ACM filter details.


Flags for enumerating the filters for a given filter tag. The following values are defined.

Value Meaning
ACM_FILTERENUMF_DWFILTERTAG The dwFilterTag member of the WAVEFILTER structure pointed to by the pwfltr member of the ACMFILTERDETAILS structure is valid. The enumerator will enumerate only a filter that conforms to this attribute. The dwFilterTag member of the ACMFILTERDETAILS structure must be equal to the dwFilterTag member of the WAVEFILTER structure.

Return Values

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

Value Description
ACMERR_NOTPOSSIBLE The details for the filter cannot be returned.
MMSYSERR_INVALFLAG At least one flag is invalid.
MMSYSERR_INVALHANDLE The specified handle is invalid.
MMSYSERR_INVALPARAM At least one parameter is invalid.


The acmFilterEnum function will return MMSYSERR_NOERROR (zero) if no suitable ACM drivers are installed. Moreover, the callback function will not be called.

The following functions should not be called from within the callback function: acmDriverAdd, acmDriverRemove, and acmDriverPriority.


  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.
  Unicode: Implemented as Unicode and ANSI versions on Windows NT/2000/XP.

See Also

Audio Compression Manager, Audio Compression Functions, WAVEFILTER, ACMFILTERDETAILS, acmDriverAdd, acmDriverRemove, acmDriverPriority