Windows Media Audio Decoder

Article
03/22/2021

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 constant	Format tag value	Audio format
WAVE_FORMAT_WMAUDIO2	0x0161	Windows Media Audio Standard
WAVE_FORMAT_WMAUDIO3	0x0162	Windows Media Audio Professional
WAVE_FORMAT_WMAUDIO_LOSSLESS	0x0163	Windows 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 constant	Format tag value	Audio format
WAVE_FORMAT_PCM	0x0001	PCM format
WAVE_FORMAT_IEEE_FLOAT	0x0003	IEEE floating point
WAVE_FORMAT_EXTENSIBLE	0xFFFE	PCM/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 XP	A Windows Media Audio decoder always behaves as a DMO.
Windows Vista	By 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 7	By 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

Requirement	Value
Client	Windows XP, Windows Vista or Windows 7
Header	Wmcodecdsp.h
DLL	Wmadmod.dll

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