Windows Media Audio 9 Codec
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The Windows Media Audio 9 encoder object is instantiated using the class identifier CLSID_CWMAEncMediaObject. The decoder object is instantiated using the class identifier CLSID_CWMADecMediaObject. Windows Media Audio 9 encoded content is identified by the audio tag 0x161.
Encoder Properties
The following properties can be set on the Windows Media Audio 9 encoder.
| Property | Description |
| MFPKEY_BAVG | Specifies the buffer window, in milliseconds, of a constrained variable-bit-rate (VBR) stream at its average bit rate (specified by MFPKEY_RAVG). |
| MFPKEY_BMAX | Specifies the buffer window, in milliseconds, of a constrained variable-bit-rate (VBR) stream at its peak bit rate (specified by MFPKEY_RMAX). |
| MFPKEY_DECODERCOMPLEXITYPROFILE | Specifies the device conformance template to which the encoded content conforms. |
| MFPKEY_ENDOFPASS | Specifies the end of an encoding pass. |
| MFPKEY_MAXENCLATENCYMS | Specifies the maximum latency for the encoder, in milliseconds. |
| MFPKEY_PASSESRECOMMENDED | Specifies the maximum number of passes supported by the codec. |
| MFPKEY_PASSESUSED | Specifies the number of passes that the codec will use to encode the content. |
| MFPKEY_RAVG | Specifies the average bit rate, in bits per second, used for 2-pass variable-bit-rate (VBR) encoding. |
| MFPKEY_RMAX | Specifies the peak bit rate, in bits per second, used for constrained 2-pass variable-bit-rate (VBR) encoding. |
| MFPKEY_VBRENABLED | Specifies whether the codec will use variable-bit-rate (VBR) encoding. |
| MFPKEY_WMAENC_AVGBYTESPERSEC | Specifies the average bytes per second in a quality-based variable-bit-rate (VBR) audio stream. |
| MFPKEY_WMAENC_ORIGWAVEFORMAT | Specifies the WAVEFORMATEX structure describing the input audio content. |
Decoder Properties
The following properties can be read on the Windows Media Audio 9 decoder.
| Property | Description |
| MFPKEY_Decoder_MaxNumPCMSamplesWithPaddedSilence | Specifies the maximum number of additional PCM samples that might be returned at the end of decoding a file. |
The following properties can be set on the Windows Media Audio 9 decoder.
| Property | Description |
| MFPKEY_BMAX | Specifies the buffer window, in milliseconds, of a constrained variable-bit-rate (VBR) stream at its peak bit rate (specified by MFPKEY_RMAX). |
| MFPKEY_ENDOFPASS | Specifies the end of an encoding pass. |
| MFPKEY_MAXDECLATENCYMS | Specifies the maximum latency for the decoder, in milliseconds. |
| MFPKEY_PASSESRECOMMENDED | Specifies the maximum number of passes supported by the codec. |
| MFPKEY_PASSESUSED | Specifies the number of passes that the codec will use to encode the content. |
| MFPKEY_RMAX | Specifies the peak bit rate, in bits per second, used for constrained 2-pass variable-bit-rate (VBR) encoding. |
| MFPKEY_VBRENABLED | Specifies whether the codec will use variable-bit-rate (VBR) encoding. |
Remarks
An audio encoder or decoder object exposes the IMediaObject interface so that the object can be used as a DirectX Media Object (DMO), and the IMFTransform interface so that the object can be used as a Media Foundation Transform (MFT).
A Windows Media Audio 9 encoder or 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 9 encoder or decoder behaves as a DMO or an MFT.
| Operating system | Encoder or decoder behavior |
| Windows XP | A Windows Media Audio 9 encoder or decoder always behaves as a DMO. |
| Windows Vista | By default, a Windows Media Audio 9 encoder or decoder behaves as a DMO. If you obtain an IMFTransform interface or an IPropertyStore interface on an Audio 9 encoder or decoder, it behaves as an MFT. |
| Windows 7 | By default, a Windows media Audio 9 encoder or decoder behaves as a DMO. If you obtain an IMFTransform interface on an Audio 9 encoder or decoder, it behaves as an MFT. |
Requirements
Client: Requires Windows 7, Windows Vista, or Windows XP.
Header: Include wmcodecdsp.h.
Library: Use wmadmoe.dll for the encoder or wmadmod.dll for the decoder.
See Also