Windows Media Audio Encoder

Article
03/22/2021

The Windows Media Audio encoder encodes audio streams. The encoder supports three categories of encoded output: Windows Media Audio Standard, Windows Media Audio Professional, and Windows Media Audio Lossless.

Class Identifier

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

Input Formats

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

Output Formats

The following table shows the audio format tags that represent the output categories supported by the Windows Media Audio encoder.

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

Interfaces

An audio endoder 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 encoder 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 encoder behaves as a DMO or an MFT.

Operating system	Encoder behavior
Windows XP	A Windows Media Audio encoder always behaves as a DMO.
Windows Vista	By default, a Windows Media Audio encoder behaves as a DMO. If you obtain an IMFTransform interface or an IPropertyStore interface on an audio encoder, it behaves as an MFT.
Windows 7	By default, a Windows Media Audio encoder behaves as a DMO. If you obtain an IMFTransform interface on an audio encoder, it behaves as an MFT.

Encoder Properties

The Windows Media Audio encoder supports the following properties.

Property	Description
MFPKEY_AVGCONSTRAINED	Specifies whether the encoder uses average-controllable VBR encoding. Windows Vista and later. Standard, Professional, Lossless. Read/write.
MFPKEY_BMAX	Specifies the buffer window, in milliseconds, of a constrained variable-bit-rate (VBR) stream at its peak bit rate. Windows XP and later. Standard, Professional. Read/write.
MFPKEY_CHECKDATACONSISTENCY2P	Specifies whether the encoder should check for data consistency across passes when performing two-pass VBR encoding. Windows Vista and later. Standard, Professional, Lossless. Read-only.
MFPKEY_CONSTRAINDECLATENCY	Specifies whether the encoder is constrained by a maximum decoder latency requirement. Windows Vista and later. Standard, Professional, Lossless. Read/write.
MFPKEY_CONSTRAINENCCOMPLEXITY	Specifies whether the complexity of the encoding algorithm is constrained. Windows Vista and later. Standard, Professional, Lossless. Read/write.
MFPKEY_CONSTRAINENCLATENCY	Specifies whether the encoder is constrained by a maximum latency requirement. Windows Vista and later. Standard, Professional, Lossless. Read/write.
MFPKEY_CONSTRAIN_ENUMERATED_VBRQUALITY	Specifies whether modes enumerated by the encoder are limited to those that meet a quality requirement. Windows Vista and later. Standard, Professional, Lossless. Read/write.
MFPKEY_DECODERCOMPLEXITYPROFILE	Specifies the complexity profile of the encoded content. Windows XP and later. Standard, Professional, Lossless. Read-only.
MFPKEY_DESIRED_VBRQUALITY	Specifies the desired quality level for VBR encoding. Windows Vista and later. Standard, Professional, Lossless. Write-only.
MFPKEY_DYN_ALLOW_NOISESUB	Specifies whether the encoder uses noise substitution. Windows Vista and later. Standard, Professional, Lossless. Read/write.
MFPKEY_DYN_ALLOW_PCMRANGELIMITING	Specifies whether the encoder uses PCM range limiting. Windows Vista and later. Standard, Professional, Lossless. Read/write.
MFPKEY_DYN_BANDTRUNC_BWCEIL	Specifies the maximum coded bandwidth allowed by band truncation in the encoder. Windows Vista and later. Standard, Professional, Lossless. Read/write.
MFPKEY_DYN_BANDTRUNC_BWFLOOR	Specifies the minimum coded bandwidth allowed by band truncation in the encoder. Windows Vista and later. Standard, Professional, Lossless. Read/write.
MFPKEY_DYN_BANDTRUNC_QCEIL	Specifies the quality at which minimum coded bandwidth is allowed. Windows Vista and later. Standard, Professional, Lossless. Read/write.
MFPKEY_DYN_BANDTRUNC_QFLOOR	Specifies the quality at which maximum coded bandwidth is allowed. Windows Vista and later. Standard, Professional, Lossless. Read/write.
MFPKEY_DYN_BANDTRUNCATION	Specifies whether the encoder performs band truncation. Windows Vista and later. Standard, Professional, Lossless. Read/write.
MFPKEY_DYN_SIMPLEMASK	Specifies whether the encoder uses the style of mask computation performed by version 7 of the Windows Media Audio encoder. Windows Vista and later. Standard, Professional, Lossless. Read/write.
MFPKEY_DYN_STEREO_PREPROC	Specifies whether the encoder performs stereo image processing. Windows Vista and later. Standard, Professional, Lossless. Read/write.
MFPKEY_DYN_VBR_BAVG	Specifies the buffer window, in milliseconds, for an encoder that is configured to use average-controllable VBR encoding. Windows Vista and later. Standard, Professional, Lossless. Read/write.
MFPKEY_DYN_VBR_RAVG	Specifies the average bit rate, in bits per second, for an encoder that is configured to use average-controllable VBR encoding. Windows Vista and later. Standard, Professional, Lossless. Read/write.
MFPKEY_ENCCOMPLEXITY	Specifies the complexity of the encoding algorithm. Windows Vista and later. Standard, Professional, Lossless. Read/write.
MFPKEY_ENDOFPASS	Specifies the end of an encoding pass. Windows XP and later. Standard, Professional. Write-only.
MFPKEY_ENHANCED_WMA	Specifies whether the core encoder uses the "Plus" feature. Windows Vista and later. Professional. Read/write.
MFPKEY_MAXDECLATENCYMS	Specifies the maximum latency for the decoder, in milliseconds. Windows Vista and later. Standard, Professional, Lossless. Write-only.
MFPKEY_MAXENCLATENCYMS	Specifies the maximum latency for the encoder, in milliseconds. Windows Vista and later. Standard, Professional, Lossless. Write-only.
MFPKEY_MOST_RECENTLY_ENUMERATED_VBRQUALITY	Specifies the VBR quality level of the most recently enumerated output type. Windows Vista and later. Standard, Professional, Lossless. Read-only.
MFPKEY_PASSESRECOMMENDED	Specifies the maximum number of passes supported by the encoder. Windows XP and later. Standard, Professional, Lossless. Read-only.
MFPKEY_PASSESUSED	Specifies the number of passes that the encoder will use to encode the content. Windows XP and later. Standard, Professional, Lossless. Read/write.
MFPKEY_PEAKCONSTRAINED	Specifies whether the encoder is constrained by a peak bit rate. Windows Vista and later. Standard, Professional. Read/write.
MFPKEY_PREFERRED_FRAMESIZE	Specifies the preferred number of samples per frame. Windows Vista and later. Professional. Read/write.
MFPKEY_REQUESTING_A_FRAMESIZE	Specifies whether the encoder should use a preferred frame size. Windows Vista and later. Professional. Read/write.
MFPKEY_RMAX	Specifies the peak bit rate, in bits per second, used for constrained 2-pass variable-bit-rate (VBR) encoding. Windows XP and later. Standard, Professional. Read/write.
MFPKEY_STAT_BAVG	Specifies the average buffer window, in milliseconds, of an encoded stream. Windows XP and later. Standard, Professional, Lossless. Read-only.
MFPKEY_STAT_BMAX	Specifies the maximum buffer window, in milliseconds, of an encoded stream. Windows XP and later. Standard, Professional, Lossless. Read-only.
MFPKEY_STAT_RAVG	Specifies the average bit rate, in bits per second, of an encoded stream. Windows XP and later. Standard, Professional, Lossless. Read-only.
MFPKEY_STAT_RMAX	Specifies the maximum bit rate, in bits per second, of an encoded stream. Windows XP and later. Standard, Professional, Lossless. Read-only.
MFPKEY_VBRENABLED	Specifies whether the encoder uses VBR encoding. Windows XP and later. Standard, Professional, Lossless. Read/write.
MFPKEY_WMA_ELEMENTARY_STREAM	This property is currently not used by the Windows Media Audio codec.
MFPKEY_WMADRC_AVGREF	Specifies the average volume level of audio content. Windows XP and later. Standard, Professional, Lossless. Read-only.
MFPKEY_WMADRC_PEAKREF	Specifies the highest volume level occurring in audio content. Windows XP and later. Standard, Professional, Lossless. Read-only.
MFPKEY_WMAENC_AVGBYTESPERSEC	Specifies the average bytes per second for VBR encoded audio. Windows XP and later. Standard, Professional, Lossless. Read-only.
MFPKEY_WMAENC_BUFFERLESSCBR	Specifies whether the encoder should produce 1 WMA packet per frame. Windows Vista and later. Standard, Professional, Lossless. Read/write.
MFPKEY_WMAENC_GENERATE_DRC_PARAMS	Specifies whether the encoder should generate dynamic range control parameters. Windows Vista and later. Standard, Professional, Lossless. Read/write.
MFPKEY_WMAENC_ORIGWAVEFORMAT	Specifies the WAVEFORMATEX structure describing the input audio content. Windows XP and later. Standard, Professional. Read/write.
MFPKEY_WMAENC_RTSPDIF	Specifies whether the encoder should enable real-time S/PDIF encoding . Windows Vista and later. Professional. Read/write.

Requirements

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

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