Windows Media Audio Decoder

The Windows Media Audio decoder decodes audio streams that were encoded by the Windows Media Audio Encoder. The encoder and decoder support three categories of encoded audio: Windows Media Audio Standard, Windows Media Audio Professional, and Windows Media Audio Lossless.

Class Identifier

The class identifier (CLSID) for the Windows Media Audio decoder is represented by the constant CLSID_CWMADecMediaObject. You can create an instance of the audio decoder by calling CoCreateInstance.

Input Formats

The following table shows the audio format tags that represent the input categories supported by the Windows Media Audio decoder. For information about how to set the input and output types for the decoder, see Configuring Audio Decoding.

Format tag constantFormat tag valueAudio format
WAVE_FORMAT_WMAUDIO20x0161Windows Media Audio Standard
WAVE_FORMAT_WMAUDIO30x0162Windows Media Audio Professional
WAVE_FORMAT_WMAUDIO_LOSSLESS0x0163Windows Media Audio Lossless

 

Output Formats

The following table shows the audio format tags that represent the output types supported by the Windows Media Audio Decoder. For information about how to set the input and output types for the decoder, see Configuring Audio Encoding.

Format tag constantFormat tag valueAudio format
WAVE_FORMAT_PCM 0x0001PCM format
WAVE_FORMAT_IEEE_FLOAT0x0003IEEE floating point
WAVE_FORMAT_EXTENSIBLE0xFFFEPCM/IEEE format in WAVEFORMATEXTENSIBLE structure

 

Interfaces

An audio decoder object exposes the IMediaObject interface so that the object can be used as a DirectX Media Object (DMO), and it exposes the IMFTransform interface so that the object can be used as a Media Foundation Transform (MFT).

A Windows Media Audio decoder behaves as a DMO or an MFT depending on which interfaces you obtain and which version of Windows is running. The following table shows the conditions under which an audio decoder behaves as a DMO or an MFT.

Operating system Decoder behavior
Windows XPA Windows Media Audio decoder always behaves as a DMO.
Windows VistaBy default, a Windows Media Audio decoder behaves as a DMO. If you obtain an IMFTransform interface or an IPropertyStore interface on an audio decoder, it behaves as an MFT.
Windows 7By default, a Windows Media Audio decoder behaves as a DMO. If you obtain an IMFTransform interface on an audio decoder, it behaves as an MFT.

 

Properties

The Windows Media Audio decoder supports the following properties.

Property Description
MFPKEY_Decoder_MaxNumPCMSamplesWithPaddedSilence

Specifies the maximum number of additional PCM samples that might be returned at the end of decoding a file.

Windows Vista and later.
Standard, Professional, Lossless.
Read-only.
MFPKEY_WMADEC_DRCMODE

Specifies the dynamic-range control mode that the audio decoder will use.

Windows XP and later.
Standard, Professional, Lossless.
Write-only.
MFPKEY_WMADEC_FOLDDOWN_MATRIX

Specifies the author-supplied fold-down coefficients for decoding multichannel audio for fewer channels than the encoded stream contains.

Windows XP and later.
Professional
Write-only.
MFPKEY_WMADEC_HIRESOUTPUT

Specifies whether the audio decoder should deliver high-resolution output.

Windows XP and later.
Professional, Lossless.
Write-only.
MFPKEY_WMADEC_LTRTOUTPUT

Specifies whether the audio decoder should perform Lt-Rt fold down.

Windows Vista and later.
Professional.
Write-only.
MFPKEY_WMADEC_SPKRCFG

Specifies the speaker configuration on the client computer.

Windows XP and later.
Professional.
Write-only.
MFPKEY_WMADRC_AVGREF

Specifies the average volume level of audio content.

Windows XP and later.
Professional, Lossless.
Read/write.
MFPKEY_WMADRC_AVGTARGET

Specifies the desired average volume level of output audio content.

Windows XP and later.
Professional, Lossless.
Write-only.
MFPKEY_WMADRC_PEAKREF

Specifies the highest volume level occurring in audio content.

Windows XP and later.
Professional, Lossless.
Read/write.
MFPKEY_WMADRC_PEAKTARGET

Specifies the desired maximum volume level of output audio content.

Windows XP and later.
Professional, Lossless.
Write-only.

 

Requirements

Client

Windows XP, Windows Vista, or Windows 7

Header

Wmcodecdsp.h

DLL

Wmadmod.dll

See also

Codec Objects
Codec Implementation

 

 

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