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MPEG Audio Decoder

The Microsoft MPEG Audio Decoder is a synchronous Media Foundation Transform (MFT) that enables decoding MPEG audio elementary stream formats using the Media Foundation (MF) pipeline.

The decoder supports the following MPEG elementary stream formats.

  • MPEG-1 audio layers I and II (ISO/IEC 11172-3). 2. MPEG-2 backward-compatible, layers I and II (ISO

  • MPEG-2 backward-compatible, layers I and II (ISO/IEC 13818-3), mono and stereo only

Class Identifier

The class identifier (CLSID) of the MPEG Audio decoder is CLSID_MSMPEGAudDecMFT, defined in the header file wmcodecdsp.h.

Input Media Types

The MPEG Audio decoder supports the following input media type attributes.

AttributeValue
MF_MT_MAJOR_TYPE MFMediaType_Audio
MF_MT_SUBTYPE MFAudioFormat_MPEG
MF_MT_AUDIO_NUM_CHANNELS

(Optional) Usually 1 for mono or 2 for stereo, but can be up to 6 channels.

MF_MT_AUDIO_CHANNEL_MASK

(Optional) Usually 0x4 for mono or 0x3 for stereo, but can also be any one of the channel masks associated with up to 6 channels (3/2/1, 3/2, 3/1, 2/2, 2/1). If present, the channel mask must be consistent with the specified input number of channels.

MF_MT_AUDIO_SAMPLES_PER_SECOND

(Optional) One of the following: 16000, 22050, 24000, 32000, 44100, 48000. If specified, the input sampling rate must be one of the valid MPEG sampling rates.

 

Output Media Types

The MPEG Audio decoder will support up to four output media subtypes, in the following order.

1. Stereo, floating point.

2. Stereo, 16-bit PCM.

3. Mono, floating point (only if the input is mono or dual-mono).

4. Mono, 16-bit PCM (only if the input is mono or dual-mono).

The decoder always supports stereo output and it is enumerated as the first output media type.

The decoder supports the following output media type attributes.

AttributeValue
MF_MT_MAJOR_TYPE MFMediaType_Audio
MF_MT_SUBTYPE Either MFAudioFormat_PCM or MFAudioFormat_Float
MF_MT_AUDIO_BITS_PER_SAMPLE 16 or 32
MF_MT_AUDIO_NUM_CHANNELS 1 or 2
MF_MT_AUDIO_CHANNEL_MASK 0x4 for mono or 0x3 for stereo
MF_MT_AUDIO_SAMPLES_PER_SECOND

One of the following: 16000, 22050, 24000, 32000, 44100, 48000.

 

Transform Attributes

The MPEG Audio decoder implements the IMFTransform::GetAttributes method. Applications can use this method to get or set the following attributes.

AttributeDescription
CODECAPI_AVDecAudioDualMono Specifies whether 2-channel audio being decoded is dual mono or not. Read-only. Set by the MFT. For more information see eAVDecAudioDualMono.
CODECAPI_AVDecAudioDualMonoReproMode

Specifies how the decoder reproduces dual mono audio. The default value is eAVDecAudioDualMonoReproMode_LEFT_MONO.

Read/Write. Applications can set this property to change the default behavior. For more information see eAVDecAudioDualMono.

CODECAPI_AVEncCommonMeanBitRate Specifies the compressed stream bit rate. Read-only. Set by the MFT.

 

 

 

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