Using High-Definition Audio

High-definition audio, in the context of the Windows Media Audio codecs, is any audio type with more than two channels or more than 16 bits per sample. High-definition audio is supported by the Windows Media Audio Professional codec and the Windows Media Audio Lossless codec.

Uncompressed high-definition audio types are defined using the WAVEFORMATEXTENSIBLE structure. WAVEFORMATEXTENSIBLE is a structured extension of the WAVEFORMATEX structure. The formattype member of DMO_MEDIA_TYPE structure that describes a high-definition audio type is set to WMCFORMAT_WaveFormatEx, just as it is for normal audio; there is no special format identifier for WAVEFORMATEXTENSIBLE. If a format uses WAVEFORMATEXTENSIBLE , the cbSize member of the WAVEFORMATEX structure is set to 22.

The multi-channel output types supported by the Windows Media Audio Professional codec do not use WAVEFORMATEXTENSIBLE, but report the correct number of channels and bits per sample in the WAVEFORMATEX structure. As with all audio types describing compressed Windows Media Audio content, there is additional information appended to the WAVEFORMATEX structure that is used by the decoder for decompression.

Decoding High-Definition Audio

To decode high-definition audio, you must set the MFPKEY_WMADEC_HIRESOUTPUT property to TRUE. If this property is not set, the decoder will deliver stereo content with a maximum of 16 bits per sample, regardless of the compressed format.

Note   High-definition audio is only supported for Microsoft Windows XP. Windows Media Audio content encoded with high-definition is rendered as two-channel audio with a maximum of 16 bits per sample on earlier versions of Windows.

See Also

• Using the Windows Media Audio Professional Codec
• Working with Audio