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 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.
Standard, Professional, Lossless. Read-only. |
| MFPKEY_WMADEC_DRCMODE | Specifies the dynamic-range control mode that the audio decoder will use.
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.
Professional Write-only. |
| MFPKEY_WMADEC_HIRESOUTPUT | Specifies whether the audio decoder should deliver high-resolution output.
Professional, Lossless. Write-only. |
| MFPKEY_WMADEC_LTRTOUTPUT | Specifies whether the audio decoder should perform Lt-Rt fold down.
Professional. Write-only. |
| MFPKEY_WMADEC_SPKRCFG | Specifies the speaker configuration on the client computer.
Professional. Write-only. |
| MFPKEY_WMADRC_AVGREF | Specifies the average volume level of audio content.
Professional, Lossless. Read/write. |
| MFPKEY_WMADRC_AVGTARGET | Specifies the desired average volume level of output audio content.
Professional, Lossless. Write-only. |
| MFPKEY_WMADRC_PEAKREF | Specifies the highest volume level occurring in audio content.
Professional, Lossless. Read/write. |
| MFPKEY_WMADRC_PEAKTARGET | Specifies the desired maximum volume level of output audio content.
Professional, Lossless. Write-only. |
Requirements
| Requirement | Value |
|---|---|
| Client |
Windows XP, Windows Vista or Windows 7 |
| Header |
|
| DLL |
|
See also
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