ACM Wrapper Filter

The ACM Wrapper filter enables Audio Compression Manager (ACM) codecs to join a filter graph. It can act either as a decompression filter or as a compression filter.

As a decompression filter, the ACM Wrapper appears in the "DirectShow Filters" category (CLSID_LegacyAmFilterCategory) and has a merit of MERIT_NORMAL. The connection media type on the input pin determines which codec the filter uses. Typically, the application does not need to add the filter to the filter graph; it is pulled in automatically by the Filter Graph Manager when needed. Decompression is only to PCM audio.

As a compression filter, the ACM Wrapper appears in the "Audio Compressors" category (CLSID_AudioCompressorCategory) and has a merit of MERIT_DO_NOT_USE. Each codec appears as a separate instance. For compression, you cannot directly create the filter with CoCreateInstance. Instead, you must use the system device enumerator. For more information, see Using the System Device Enumerator.

Filter interfaces IBaseFilter, IPersist, IPersistPropertyBag
Input pin media typesMEDIATYPE_Audio, MEDIASUBTYPE_NULL, FORMAT_WaveFormatEx
Input pin interfaces IMemInputPin, IPin, IQualityControl
Output pin media typesMEDIATYPE_Audio, MEDIASUBTYPE_PCM, FORMAT_WaveFormatEx.

Any combination of the following are possible:

  • Samples per second (kHz): 44.1, 22.05, 11.025, or 8.0.
  • Channels: Stereo or mono.
  • Bits per sample: 8 or 16.
Output pin interfaces IAMStreamConfig, IMediaPosition, IMediaSeeking, IPin, IQualityControl
Filter CLSIDCLSID_ACMWrapper
Property Page CLSIDNo property page.
ExecutableQuartz.dll
Merit MERIT_NORMAL or MERIT_DO_NOT_USE
Filter Category CLSID_LegacyAmFilterCategory or CLSID_AudioCompressorCategory

 

Related topics

DirectShow Filters

 

 

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