Musepack or MPC is an open source lossy audio codec, specifically optimized for transparent compression of stereo audio at bitrates of 160–180 (manual set allows bitrates up to 320) kbit/s. It was formerly known as MPEGplus, MPEG+ or MP+.
Development of MPC was initiated in 1997 by Andree Buschmann and later taken over by Frank Klemm, and is currently maintained by the Musepack Development Team (MDT) with assistance from Frank Klemm and Andree Buschmann. Encoders and decoders are available for Microsoft Windows, Linux and Mac OS X, along with plugins for several third-party media players available from the Musepack website, licensed under the LGPL or BSD licenses, and an extensive list of programs supporting the format.
The psychoacoustic model of MPC is based on MPEG ISO model 2, but is extended by CVD (clear voice detection). The quantization algorithm of the MPC encoder performs spectral shaping of the noise, called adaptive noise shaping (ANS), in order to overcome the low frequency resolution of the polyphase quadrature filter bands.
In the past, MPC has been under suspicion of violating multiple patents (MP2, PNS, subband). According to the developers of MPC, all patented code has been removed and it is now believed to be free of patent encumbrance. However, one PNS patent application is still active, and it is not trivial to know if MPC's own "noise substitution techniques" avoid its scope or not. Only a careful examination by a patent lawyer would say whether Musepack is truly patentless or not.
Musepack is mainly optimized for transparent encoding at the "--standard" preset (175-185 kbit/s). Very few optimisations have been made at lower bitrates (like 128 kbit/s). Nevertheless, various listening tests have been conducted in which Musepack has performed well at both lower and higher bitrates.
Despite being optimized for 100% transparency at moderately high bitrates, MPC has scored highly on many 128 kbit/s tests. In May 2004, a series of double-blind listening tests (as reported on Slashdot) suggested that Musepack and Ogg Vorbis (which was the 1.1 "aoTuV" fork at the time) were the two best available codecs for high-quality audio compression at bitrates around 128kbit/s, beating MP3, AAC, WMA, and ATRAC.
Listening tests of MPC:
Musepack distributes the libmpcdec library for decoding MPC content. Various plugins have been developed, using that library, including for the XMMS player.
Software players capable of using DirectShow filters also can play Musepack files, for example by Monogram's DS filters. If you need to convert audio from Musepack to other audio formats you can use for example Audio Transcoder
There is a list of applications (players, taggers, frontends, CD rippers and burners etc.) supporting Musepack at the official website.