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 since 1997 it has
rapidly developed and vastly improved and is now at an advanced stage in which
it contains heavily optimized and patentless code.