Windows Media MP3 Decoder

The Windows Media MP3 decoder decodes audio files that have been encoded in the following formats.

  • ISO/IEC 11172-3 (MPEG-1 Audio) Layer 3
  • ISO/IEC 13818-3 (MPEG-2 Audio) Layer 3, low sampling frequency extension

Class Identifier

The class identifier (CLSID) for the Windows Media MP3 decoder is represented by the constant CLSID_CMP3DecMediaObject. You can create an instance of the MP3 decoder by calling CoCreateInstance.

Interfaces

An MP3 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 MP3 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 a Windows Media MP3 decoder behaves as a DMO or an MFT.

Operating system Decoder behavior
Windows XP A Windows Media MP3 decoder always behaves as a DMO.
Windows Vista By default, a Windows Media MP3 decoder behaves as a DMO. If you obtain an IMFTransform interface or an IPropertyStore interface on a Windows Media MP3 decoder, it behaves as an MFT.
Windows 7 By default, a Windows Media MP3 decoder behaves as a DMO. If you obtain an IMFTransform interface on a Windows Media MP3 decoder, it behaves as an MFT.

 

Input Formats

The following table shows the audio format tag that represents the input type supported by the Windows Media MP3 decoder.

Format tag constant Format tag value Audio format
WAVE_FORMAT_MPEGLAYER3 0x55 ISO MPEG Layer 3

 

Output Formats

The following table shows the audio format tags that represent the output types supported by the Windows Media MP3 decoder.

Format tag constant Format tag value Audio format
WAVE_FORMAT_PCM 0x0001 PCM format (when used as a DMO or an MFT)
WAVE_FORMAT_IEEE_FLOAT 0x0003 IEEE floating point (when used as an MFT)
WAVE_FORMAT_EXTENSIBLE 0xFFFE PCM/IEEE format in WAVEFORMATEXTENSIBLE structure (when used as an MFT)

 

The Windows Media MP3 decoder supports and enumerates the following output media types.

  • An output type that has the same sampling rate and number of channels as the input type.
  • Mono output for stereo input.
  • Output types with bit depths of 8 and 16.
  • Floating point output, if the decoder is behaving as an MFT.

The Windows Media MP3 decoder supports, but does not enumerate, the following output media types.

  • An output type that has half the sampling rate of the input type.
  • An output type that has one fourth the sampling rate of the input type.

Requirements

Client
Windows XP, Windows Vista or Windows 7
Header
Wmcodecdsp.h
DLL
Mp3dmod.dll

See also

Codec Objects

Codec Implementation