A RIFF file is just a sort of tagged file thing for Multimedia stuff, rather like a TIFF is for images. WAV files _are_ RIFF files. If you put an MP3 file inside a RIFF file with the right header then you get a WAV file that is actually an MP3 file. Other compression mechanisms are also used. This is why you need to have the right codecs installed to play certain WAV files.

I believe that Windows comes with a codec from Fraunhofer that plays MP3 inside WAV files. You can probably find it in Control Panel.

WAV is not synonymous with PCM.

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Mike Crowe
I may not be speaking on behalf of empeg above :-)