Musepack or MPC is an open source lossy audio codec, specifically optimized for transparent compression of stereo audio at bitrates of 160-180 kbit/s. It was formerly known as MPEGplus, MPEG+ or MP+. Open source refers to projects that are open to the public and which draw on other projects that are freely available to the general public. ... Note: This article is about audio data compression, which reduces the data rate of digital audio signals. ... In data compression or psychoacoustics, transparency is the ideal result of lossy data compression. ... In telecommunications and computing, bit rate (sometimes written bitrate) is the frequency at which bits are passing a given (physical or metaphorical) point. It is quantified using the bit per second (bit/s) unit. ...

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. 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. Microsoft Windows is a series of popular proprietary operating environments and operating systems created by Microsoft for use on personal computers and servers. ... Tux is the official Linux mascot. ... Mac OS X is the operating system that is included with all currently shipping Apple Macintosh computers in the education, the consumer, and in the business markets. ... GNU logo The GNU Lesser General Public License (formerly the GNU Library General Public License) is an FSF approved free software license designed as a compromise between the GNU General Public License and simple permissive licenses such as the BSD license and the MIT License. ... The BSD license is an acronym for the Berkeley Software Distribution license agreement, and is one of the most widely used licenses for free software (a subset of open source software). ...

Technical details

Musepack was developed using the MP2 codec as a starting point, but many features have since been added, including: MP2 (sometimes incorrectly named Musicam) is a short form of MPEG-1 Audio Layer II, and it is also used as a file extension for files containing audio data of this type. ...

• subband-wise selectable M/S encoding (as in AAC)
• Huffman coding (as in MP3 and AAC, but more efficient)
• noise substitution techniques (as in ATSC A-52 and MPEG-4 AAC V2)
• pure variable bitrate between 3 and 1300 kbit/s (when needed)

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. To meet Wikipedias quality standards, this article or section may require cleanup. ... In computer science, Huffman coding is an entropy encoding algorithm used for lossless data compression. ... MPEG Audio Layer 3, more commonly referred to as MP3, is a popular digital audio encoding and lossy compression format invented and standardized in 1991 by a team of engineers directed by the Fraunhofer Institute in Germany. ... MPEG-4, introduced in late 1998, is the designation for a group of audio and video coding standards and related technology agreed upon by the ISO/IEC Moving Picture Experts Group (MPEG). ... Psychoacoustics is the study of subjective human perception of sounds. ... A polyphase quadrature filter, or PQF is a filter bank, which splits an input signal into a given number N (mostly a power of 2) of equidistant sub-bands. ...

In the past, MPC has been under suspicion of violating multiple patents (MP2, PNS, subband) [1]. 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 [2], 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.

MPC uses the APEv2 tag metadata container. The APEv2 tag format is a modification of the APE tag format that is used by default for the WavPack (WV), Musepack (MPC) and Monkeys Audio file format as a metadata container for such information as the title, artist, album, track number or other information about the file to... Metadata (Greek: meta-+ Latin: data information), literally data about data, is information that describes another set of data. ...

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. A codec listening test is a scientific study designed to compare two or more lossy audio codecs, usually with respect to perceived fidelity and/or compression efficiency. ...

Unlike other lossy codecs, the current Stream Version (7) of Musepack does not specifically support seeking within a file (with, eg, seektables or similar constructs). Software players that support seeking do so through brute force decoding of the data between start and end seekpoints. According to Musepack developers, the next Stream Version (7.5) will aim at solving this, the format's main hurdle. In computer science, a brute-force search consists of systematically enumerating every possible solution of a problem until a solution is found, or all possible solutions have been exhausted. ...

Test results

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 [3] (as reported on Slashdot [4]) 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, or ATRAC. High Fidelity is also the title of a book by Nick Hornby and a film directed by Stephen Frears, based upon Hornbys book. ... This page is about the audio compression codec. ... MPEG Audio Layer 3, more commonly referred to as MP3, is a popular digital audio encoding and lossy compression format invented and standardized in 1991 by a team of engineers directed by the Fraunhofer Institute in Germany. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Windows Media Audio (WMA) is a proprietary compressed audio file format developed by Microsoft. ... ATRAC (Adaptive TRansform Acoustic Coding) is a proprietary audio compression algorithm used to store information on Minidiscs and other Sony-branded audio players. ...

Listening tests of MPC:

• 2005 - 185 kbit/s test [5] based on 18 classical music samples – MPC comes second to Vorbis aoTuV. (Note: Doubtful. Unlike previous tests, performed by a single person.)
• 2004 - rjamorim's second 128 kbit/s group listening test [6] - between 14 and 27 listeners. MPC and Vorbis tied for first.
• 2004 - High bitrate tests [7] (thread by a Musepack developer)
• 2003 - rjamorim's first 128 kbit/s group listening test [8] - between 14 and 29 listeners. AAC, MPC, Vorbis, and WMA tied for first.
• 2002 - ff123's second 128 kbit/s group listening test [9]
• 2001 - ff123's 128 kbit/s group listening test [10]

Hardware support

Devices supporting The Core Pocket Media Player are capable of MPC playback - those include the PocketPC and devices running Palm OS, Symbian OS, Windows, Windows CE or Windows Mobile. All devices with software audio decoding that are supported by Rockbox can also play Musepack files. Playback on Roku Photobridge HD is supported with a plugin. The Core Pocket Media Player (TCPMP) is the most versitile and dual license Media Player available today. ... A Pocket PC is a computer in a handheld size that runs a variation of the operating system Windows CE. It has many capabilities of modern desktop PCs. ... Palm OS is an operating system made by PalmSource, Inc. ... It has been suggested that EPOC (computing) be merged into this article or section. ... Microsoft Windows is a series of popular proprietary operating environments and operating systems created by Microsoft for use on personal computers and servers. ... Windows CE for Handheld PC 3. ... Windows Mobile is a compact operating system for mobile devices based on the Microsoft Win32 API. Devices which run Windows Mobile include Pocket PCs, Smartphones, and Portable Media Centers. ... Rockbox is a GPL open source operating system for digital audio players (DAPs). ... Roku, founded in 2002, is a Palo Alto based consumer electronics firm which specialises in home digital media products. ...

External links

• Musepack.net – Official website/forums of the Musepack project (encoders, decoders, plugins for XMMS, Beep Media Player and Winamp)
• Frank Klemm's MPC page
• Musepack forum at Hydrogenaudio.org