Specifies the WAVEFORMATEX structure describing the input audio content.

Constant for IPropertyBag


Data Type

VT_ARRAY | VT_UI1 (WAVEFORMATEX as an array of bytes)


When transcoding Windows Media Audio-based content to a lower bit rate, you can pass the WAVEFORMATEX structure of the content to the codec to enable the codec to optimize its algorithms. This feature, called smart recompression, provides better results than decompressing the content and then feeding the reconstructed PCM samples back through the codec.

When passing the WAVEFORMATEX structure, include any extra bytes at the end of the structure specified by WAVEFORMATEX.cbSize.

The audio encoder accepts only inputs and outputs for which the number of channels, bits per sample, and sample rate are identical. You can transcode content only to a lower bit rate within those parameters. In any case, you must decode the content and pass the uncompressed samples as input to the encoder. Setting this property gives the encoder some information about the processing that has already been performed on the content.


Minimum supported client
Windows XP [desktop apps only]
Minimum supported server
Windows Server 2003 [desktop apps only]

See also

Media Foundation Properties