Windows Media Audio 9 Codec

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 XP, Windows Vista, or Windows 7.
Header Declared in Wmcodecdsp.h.
Library Use Wmadmoe.dll for the encoder or wmadmod.dll for the decoder.

See Also

Codec Objects
Codec Implementation
Using the Windows Media Audio 9 Codec

Send comments about this topic to Microsoft

Build date: 1/27/2009