Ronald Bultje has been a long-time contributor to a variety of open source multimedia projects. He was keen to try his hand at reverse engineering and implementing an undiscovered codec. Most people start simple, but Ronald went for a vocoder (significantly more complex than the piddly little ADPCM codecs I started with). He has completed his reverse engineering of the Windows Media Audio 9 Voice algorithm and committed a decoder for FFmpeg. If you’re interested in the technical details, check out Ronald’s blog posts on the matter: Codec Woes and WMA Voice Codec Dissection.
Here is a WMA Voice file being played in FFplay using Michael’s spectrum visualization (now the default audio visualization):