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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
| Requirement | Value |
|---|---|
| Client |
Windows XP, Windows Vista or Windows 7 |
| Header |
|
| DLL |
|
See also