Musepack is an audio compression format with a strong emphasis on high quality.
It's not lossless, but it is designed for transparency, so that you won't be
able to hear differences between the original wave file and the much smaller
MPC file.

It is based on the MPEG-1 Layer-2 / MP2 algorithms, but has rapidly developed
and vastly improved and is now at an advanced stage in which it contains
heavily optimized and patentless code.

WWW: http://www.musepack.net/