MP3
MP3 (formally MPEG-1 Audio Layer III or MPEG-2 Audio Layer III)[4] is a coding format for digital audio developed largely by the Fraunhofer Society in Germany under the lead of Karlheinz Brandenburg,[11][12] with support from other digital scientists in other countries. Originally defined as the third audio format of the MPEG-1 standard, it was retained and further extended—defining additional bit rates and support for more audio channels—as the third audio format of the subsequent MPEG-2 standard. A third version, known as MPEG-2.5—extended to better support lower bit rates—is commonly implemented but is not a recognized standard.
For other uses, see MP3 (disambiguation).Filename extension
.mp3.bit (before 1995)[1]
Karlheinz Brandenburg, Ernst Eberlein, Heinz Gerhäuser, Bernhard Grill, Jürgen Herre and Harald Popp (all of Fraunhofer Society),[5] and others
6 December 1991[6]
April 1998
Yes[9]
Expired patents[10]
MP3 (or mp3) as a file format commonly designates files containing an elementary stream of MPEG-1 Audio or MPEG-2 Audio encoded data, without other complexities of the MP3 standard.
Concerning audio compression (the aspect of the standard most apparent to end-users and for which it is best known), MP3 uses lossy data compression to encode data using inexact approximations and the partial discarding of data. This allows a large reduction in file sizes when compared to uncompressed audio. The combination of small size and acceptable fidelity led to a boom in the distribution of music over the Internet in the mid-to-late 1990s, with MP3 serving as an enabling technology at a time when bandwidth and storage were still at a premium. The MP3 format soon became associated with controversies surrounding copyright infringement, music piracy, and the file-ripping and sharing services MP3.com and Napster, among others. With the advent of portable media players, a product category also including smartphones, MP3 support remains near-universal.
MP3 compression works by reducing (or approximating) the accuracy of certain components of sound that are considered (by psychoacoustic analysis) to be beyond the hearing capabilities of most humans. This method is commonly referred to as perceptual coding or psychoacoustic modeling.[13] The remaining audio information is then recorded in a space-efficient manner using MDCT and FFT algorithms. Compared to CD-quality digital audio, MP3 compression can commonly achieve a 75–95% reduction in size. For example, an MP3 encoded at a constant bit rate of 128 kbit/s would result in a file approximately 9% the size of the original CD audio.[14] In the early 2000s, compact disc players increasingly adopted support for playback of MP3 files on data CDs.
The Moving Picture Experts Group (MPEG) designed MP3 as part of its MPEG-1, and later MPEG-2, standards. MPEG-1 Audio (MPEG-1 Part 3), which included MPEG-1 Audio Layer I, II, and III, was approved as a committee draft for an ISO/IEC standard in 1991,[15][16] finalized in 1992,[17] and published in 1993 as ISO/IEC 11172-3:1993.[7] An MPEG-2 Audio (MPEG-2 Part 3) extension with lower sample and bit rates was published in 1995 as ISO/IEC 13818-3:1995.[8][18] It requires only minimal modifications to existing MPEG-1 decoders (recognition of the MPEG-2 bit in the header and addition of the new lower sample and bit rates).
Licensing, ownership, and legislation[edit]
The basic MP3 decoding and encoding technology is patent-free in the European Union, all patents having expired there by 2012 at the latest. In the United States, the technology became substantially patent-free on 16 April 2017 (see below). MP3 patents expired in the US between 2007 and 2017. In the past, many organizations have claimed ownership of patents related to MP3 decoding or encoding. These claims led to several legal threats and actions from a variety of sources. As a result, in countries that allow software patents, uncertainty about which patents must have been licensed to create MP3 products without committing patent infringement was common in the early stages of the technology's adoption.
The initial near-complete MPEG-1 standard (parts 1, 2, and 3) was publicly available on 6 December 1991 as ISO CD 11172.[95][96] In most countries, patents cannot be filed after prior art has been made public, and patents expire 20 years after the initial filing date, which can be up to 12 months later for filings in other countries. As a result, patents required to implement MP3 expired in most countries by December 2012, 21 years after the publication of ISO CD 11172.
An exception is the United States, where patents in force but filed before 8 June 1995 expire after the later of 17 years from the issue date or 20 years from the priority date. A lengthy patent prosecution process may result in a patent issued much later than normally expected (see submarine patents). The various MP3-related patents expired on dates ranging from 2007 to 2017 in the United States.[97] Patents for anything disclosed in ISO CD 11172 filed a year or more after its publication are questionable. If only the known MP3 patents filed by December 1992 are considered, then MP3 decoding has been patent-free in the US since 22 September 2015, when U.S. patent 5,812,672, which had a PCT filing in October 1992, expired.[98][99][100] If the longest-running patent mentioned in the aforementioned references is taken as a measure, then the MP3 technology became patent-free in the United States on 16 April 2017, when U.S. patent 6,009,399, held[101] and administered by Technicolor,[102] expired. As a result, many free and open-source software projects, such as the Fedora operating system, have decided to start shipping MP3 support by default, and users will no longer have to resort to installing unofficial packages maintained by third party software repositories for MP3 playback or encoding.[103]
Technicolor (formerly called Thomson Consumer Electronics) claimed to control MP3 licensing of the Layer 3 patents in many countries, including the United States, Japan, Canada, and EU countries.[104] Technicolor had been actively enforcing these patents.[105] MP3 license revenues from Technicolor's administration generated about €100 million for the Fraunhofer Society in 2005.[106] In September 1998, the Fraunhofer Institute sent a letter to several developers of MP3 software stating that a license was required to "distribute and/or sell decoders and/or encoders". The letter claimed that unlicensed products "infringe the patent rights of Fraunhofer and Thomson. To make, sell or distribute products using the [MPEG Layer-3] standard and thus our patents, you need to obtain a license under these patents from us."[107] This led to the situation where the LAME MP3 encoder project could not offer its users official binaries that could run on their computer. The project's position was that as source code, LAME was simply a description of how an MP3 encoder could be implemented. Unofficially, compiled binaries were available from other sources.
Sisvel S.p.A., a Luxembourg-based company, administers licenses for patents applying to MPEG Audio.[108] They, along with its United States subsidiary Audio MPEG, Inc. previously sued Thomson for patent infringement on MP3 technology,[109] but those disputes were resolved in November 2005 with Sisvel granting Thomson a license to their patents. Motorola followed soon after and signed with Sisvel to license MP3-related patents in December 2005.[110] Except for three patents, the US patents administered by Sisvel[111] had all expired in 2015. The three exceptions are: U.S. patent 5,878,080, expired February 2017; U.S. patent 5,850,456, expired February 2017; and U.S. patent 5,960,037, expired 9 April 2017. As of around the first quarter of 2023, Sisvel's licensing program has become a legacy.[112]
In September 2006, German officials seized MP3 players from SanDisk's booth at the IFA show in Berlin after an Italian patents firm won an injunction on behalf of Sisvel against SanDisk in a dispute over licensing rights. The injunction was later reversed by a Berlin judge,[113] but that reversal was in turn blocked the same day by another judge from the same court, "bringing the Patent Wild West to Germany" in the words of one commentator.[114] In February 2007, Texas MP3 Technologies sued Apple, Samsung Electronics and Sandisk in eastern Texas federal court, claiming infringement of a portable MP3 player patent that Texas MP3 said it had been assigned. Apple, Samsung, and Sandisk all settled the claims against them in January 2009.[115][116]
Alcatel-Lucent has asserted several MP3 coding and compression patents, allegedly inherited from AT&T-Bell Labs, in litigation of its own. In November 2006, before the companies' merger, Alcatel sued Microsoft for allegedly infringing seven patents. On 23 February 2007, a San Diego jury awarded Alcatel-Lucent US $1.52 billion in damages for infringement of two of them.[117] The court subsequently revoked the award, however, finding that one patent had not been infringed and that the other was not owned by Alcatel-Lucent; it was co-owned by AT&T and Fraunhofer, who had licensed it to Microsoft, the judge ruled.[118] That defense judgment was upheld on appeal in 2008.[119]