{{Short description|Digital audio format}} {{Other uses}} {{Distinguish|MPEG-3}} {{Use dmy dates|date=August 2025}} {{Use American English|date=September 2023}} {{Infobox file format | name = MP3 | icon = Mp3 format logo.svg{{!}}class=skin-invert | icon_size = 200px | _noextcode = on | extension = {{code|.mp3}}<br />{{code|.mpga}} (rarely)<ref>{{cite web | title=About MP3 Audio Coding & ID3 Metadata | website=The Broadcast Bridge | date=2024-08-30 | url=https://www.thebroadcastbridge.com/content/entry/20759/standards-part-16-about-mp3-audio-coding-id3-metadata | access-date=2025-08-15}}</ref><br />{{code|.bit}} (before 1995)<ref name="mp3-name" /> | _nomimecode = on | mime = {{plainlist| * {{code|audio/mpeg}}<ref name="rfc3003" /> * {{code|audio/MPA}}<ref name="rfc3555" /> * {{code|audio/mpa-robust}}<ref name="rfc5219" /> }} | type code = | uniform type = | owner = Moving Picture Experts Group | released = {{start date and age|df=y|1991|12|06}}<ref>{{Cite book |vauthors=Patel K, Smith BC, Rowe LA |title=Proceedings of the first ACM international conference on Multimedia – MULTIMEDIA '93 |chapter=Performance of a software MPEG video decoder |date=1993-09-01 |chapter-url=https://dl.acm.org/doi/10.1145/166266.166274 |series=ACM Multimedia |location=New York City |publisher=Association for Computing Machinery |pages=75–82 |doi=10.1145/166266.166274 |isbn=978-0-89791-596-0 |s2cid=3773268 |access-date=15 December 2021 |archive-date=15 December 2021 |archive-url=https://web.archive.org/web/20211215125939/https://dl.acm.org/doi/10.1145/166266.166274 |url-status=live }} Reference 3 in the paper is to Committee Draft of Standard ISO/IEC 11172, December 6, 1991.</ref> | latest release version = ISO/IEC 13818-3:1998 | latest release date = {{Start date and age|1998|04|df=y}} | type = Lossy audio | container for = | contained by = MPEG-ES | extended from = | extended to = | standards = {{ubl |ISO/IEC 11172-3<ref name="11172-3" /> |ISO/IEC 13818-3<ref name="13818-3" />}} | open = Yes<ref>{{Cite web|url=https://www.iis.fraunhofer.de/en/ff/amm/consumer-electronics/mp3.html|title=MP3 technology at Fraunhofer IIS|archive-url=https://web.archive.org/web/20210815043015/https://www.iis.fraunhofer.de/en/ff/amm/consumer-electronics/mp3.html |archive-date=2021-08-15 |website=Fraunhofer IIS|access-date=12 June 2020}}</ref> | free = Expired patents<ref>{{cite tech report |publisher=Library of Congress |location=Washington, D.C. |series=Sustainability of Digital Formats |type=Full draft |title=MP3 (MPEG Layer III Audio Encoding) |date=3 May 2017 |url=https://www.loc.gov/preservation/digital/formats/fdd/fdd000012.shtml |access-date=1 December 2021}}</ref> | url = }}
'''MP3''' (formally '''MPEG-1 Audio Layer III''' or '''MPEG-2 Audio Layer III''')<ref name="rfc5219" /> is an audio coding format developed largely by the Fraunhofer Society in Germany under the lead of Karlheinz Brandenburg.<ref>{{Cite web|url=https://www.youtube.com/watch?v=cuU16whZ-Fs|title=73. "Father" of the MP3, Karlheinz Brandenburg|date=13 July 2015 |via=www.youtube.com|access-date=2 January 2023|archive-date=2 January 2023|archive-url=https://web.archive.org/web/20230102160404/https://www.youtube.com/watch?v=cuU16whZ-Fs|url-status=live}}</ref><ref>{{Cite web|url=https://www.internethistorypodcast.com/2015/07/on-the-20th-birthday-of-the-mp3-an-interview-with-the-father-of-the-mp3-karlheinz-brandenburg/|title=On the 20th Birthday of the MP3, An Interview With The "Father" of the MP3, Karlheinz Brandenburg|access-date=2 January 2023|archive-date=2 January 2023|archive-url=https://web.archive.org/web/20230102160403/https://www.internethistorypodcast.com/2015/07/on-the-20th-birthday-of-the-mp3-an-interview-with-the-father-of-the-mp3-karlheinz-brandenburg/|url-status=live}}</ref> It was designed to greatly reduce the amount of data required to represent audio, yet still sound like a faithful reproduction of the original uncompressed audio to most listeners; for example, compared to CD-quality digital audio, MP3 compression can commonly achieve a 75–95% reduction in size, depending on the bit rate.<ref>{{cite web |date=27 July 2017 |title=MP3 (MPEG Layer III Audio Encoding) |url=https://www.loc.gov/preservation/digital/formats/fdd/fdd000012.shtml |url-status=live |archive-url=https://web.archive.org/web/20170814015755/https://www.loc.gov/preservation/digital/formats/fdd/fdd000012.shtml |archive-date=14 August 2017 |access-date=9 November 2017 |publisher=The Library of Congress}}</ref> In popular usage, ''MP3'' often refers to files of sound or music recordings stored in the MP3 file format (<code>.mp3</code>) on consumer electronic devices.
MPEG-1 Audio Layer III was originally defined in 1991 as one of the three possible audio codecs of the MPEG-1 standard (along with MPEG-1 Audio Layer I and MPEG-1 Audio Layer II). All three options were retained and further extended—defining additional bit rates and support for more audio channels (supporting surround sound—in the subsequent MPEG-2 standard).
MP3 as a file format commonly designates files containing an elementary stream of MPEG-1 Audio or MPEG-2 Audio encoded data. Concerning audio compression, which is its most apparent element to end-users, MP3 uses lossy compression to reduce precision of encoded data and to partially discard data, allowing for 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 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 (including "MP3 players"), a product category also including smartphones, MP3 support became near-universal and it remains a ''de facto'' standard for digital audio despite the creation of newer coding formats such as AAC.
== History == 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,<ref name="cd-1991" /><ref name="neuron2-cd-1991" /> finalized in 1992,<ref name="dis-1992" /> and published in 1993 as ISO/IEC 11172-3:1993.<ref name="11172-3" /> 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.<ref name="13818-3" /><ref name="mpeg-audio-faq-bc" /> 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).
=== Background === {{Further|Linear predictive coding|Modified discrete cosine transform}}
The MP3 lossy compression algorithm takes advantage of a perceptual limitation of human hearing called auditory masking. In 1894, the American physicist Alfred M. Mayer reported that a tone could be rendered inaudible by another tone of lower frequency.<ref name="Mayer1894" /> In 1959, Richard Ehmer described a complete set of auditory curves regarding this phenomenon.<ref name="Ehmer1959" /> Between 1967 and 1974, Eberhard Zwicker did work in the areas of tuning and masking of critical frequency-bands,<ref name="Zwicker" /><ref name="Eberhard" /> which in turn built on the fundamental research in the area from Harvey Fletcher and his collaborators at Bell Labs.<ref name="Fletcher" />
Perceptual coding was first used for speech coding compression with linear predictive coding (LPC),<ref name="Schroeder2014">{{cite book |last1= Schroeder |first1= Manfred R. |title= Acoustics, Information, and Communication: Memorial Volume in Honor of Manfred R. Schroeder |date= 2014 |publisher= Springer |isbn= 978-3-319-05660-9 |chapter= Bell Laboratories |page= 388 |chapter-url= https://books.google.com/books?id=d9IkBAAAQBAJ&pg=PA388}}</ref> which has origins in the work of Fumitada Itakura (Nagoya University) and Shuzo Saito (Nippon Telegraph and Telephone) in 1966.<ref>{{cite journal |last1= Gray |first1= Robert M. |title= A History of Realtime Digital Speech on Packet Networks: Part II of Linear Predictive Coding and the Internet Protocol |journal= Found. Trends Signal Process. |date= 2010 |volume= 3 |issue= 4 |pages= 203–303 |doi= 10.1561/2000000036 |url= https://ee.stanford.edu/~gray/lpcip.pdf |issn= 1932-8346 |doi-access= free |access-date= 14 July 2019 |archive-date= 9 October 2022 |archive-url= https://ghostarchive.org/archive/20221009/https://ee.stanford.edu/~gray/lpcip.pdf |url-status= live }}</ref> In 1978, Bishnu S. Atal and Manfred R. Schroeder at Bell Labs proposed an LPC speech codec, called adaptive predictive coding, that used a psychoacoustic coding-algorithm exploiting the masking properties of the human ear.<ref name="Schroeder2014"/><ref>{{cite book |last1= Atal |first1= B. |last2= Schroeder |first2= M. |title= ICASSP '78. IEEE International Conference on Acoustics, Speech, and Signal Processing |chapter= Predictive coding of speech signals and subjective error criteria |date= 1978 |volume= 3 |pages= 573–576 |doi= 10.1109/ICASSP.1978.1170564}}</ref> Further optimization by Schroeder and Atal with J.L. Hall was later reported in a 1979 paper.<ref name="Schroeder1979"/> That same year, a psychoacoustic masking codec was also proposed by M. A. Krasner,<ref name="Krasner" /> who published and produced hardware for speech (not usable as music bit-compression), but the publication of his results in a relatively obscure Lincoln Laboratory Technical Report<ref>{{cite web|last1= Krasner|first1= M. A.|title= Digital Encoding of Speech Based on the Perceptual Requirement of the Auditory System (Technical Report 535)|url= https://apps.dtic.mil/dtic/tr/fulltext/u2/a077355.pdf|ref= Lincoln Laboratory, MIT|date= 18 June 1979|url-status= live|archive-url= https://web.archive.org/web/20170903070321/https://www.dtic.mil/dtic/tr/fulltext/u2/a077355.pdf|archive-date= 3 September 2017}}</ref> did not immediately influence the mainstream of psychoacoustic codec-development.
The discrete cosine transform (DCT), a type of transform coding for lossy compression, proposed by Nasir Ahmed in 1972, was developed by Ahmed with T. Natarajan and K. R. Rao in 1973; they published their results in 1974.<ref>{{cite journal |last= Ahmed |first= Nasir |author-link= N. Ahmed |title= How I Came Up With the Discrete Cosine Transform |journal= Digital Signal Processing |date= January 1991 |volume= 1 |issue= 1 |pages= 4–5 |doi= 10.1016/1051-2004(91)90086-Z |bibcode= 1991DSP.....1....4A |url= https://www.scribd.com/doc/52879771/DCT-History-How-I-Came-Up-with-the-Discrete-Cosine-Transform |access-date= 19 November 2019 |archive-date= 10 June 2016 |archive-url= https://web.archive.org/web/20160610013109/https://www.scribd.com/doc/52879771/DCT-History-How-I-Came-Up-with-the-Discrete-Cosine-Transform |url-status= live |url-access= subscription }}</ref><ref>{{Citation |first1= Nasir |last1= Ahmed |author1-link= N. Ahmed |first2= T. |last2= Natarajan |first3= K. R. |last3= Rao |title= Discrete Cosine Transform |journal= IEEE Transactions on Computers |date= January 1974 |volume= C-23 |issue= 1 |pages= 90–93 |doi= 10.1109/T-C.1974.223784|bibcode= 1974ITCmp.100...90A |s2cid= 149806273 }}</ref><ref>{{Citation |last1= Rao |first1= K. R. |author-link1= K. R. Rao |last2= Yip |first2= P. |title= Discrete Cosine Transform: Algorithms, Advantages, Applications |publisher= Academic Press |location= Boston |year= 1990 |isbn= 978-0-12-580203-1}}</ref> This led to the development of the modified discrete cosine transform (MDCT), proposed by J. P. Princen, A. W. Johnson and A. B. Bradley in 1987,<ref>J. P. Princen, A. W. Johnson und A. B. Bradley: ''Subband/transform coding using filter bank designs based on time domain aliasing cancellation'', IEEE Proc. Intl. Conference on Acoustics, Speech, and Signal Processing (ICASSP), 2161–2164, 1987</ref> following earlier work by Princen and Bradley in 1986.<ref>John P. Princen, Alan B. Bradley: ''Analysis/synthesis filter bank design based on time domain aliasing cancellation'', IEEE Trans. Acoust. Speech Signal Processing, ''ASSP-34'' (5), 1153–1161, 1986</ref> The MDCT later became a core part of the MP3 algorithm.<ref name="Guckert">{{cite web |last1= Guckert |first1= John |title= The Use of FFT and MDCT in MP3 Audio Compression |url= http://www.math.utah.edu/~gustafso/s2012/2270/web-projects/Guckert-audio-compression-svd-mdct-MP3.pdf |website= University of Utah |date= Spring 2012 |access-date= 14 July 2019 |archive-date= 12 February 2021 |archive-url= https://web.archive.org/web/20210212022237/http://www.math.utah.edu/~gustafso/s2012/2270/web-projects/Guckert-audio-compression-svd-mdct-MP3.pdf |url-status= live }}</ref>
Ernst Terhardt and other collaborators constructed an algorithm describing auditory masking with high accuracy in 1982.<ref name="Terhardt1982" /> This work added to a variety of reports from authors dating back to Fletcher, and to the work that initially determined critical ratios and critical bandwidths.
In 1985, Atal and Schroeder presented code-excited linear prediction (CELP), an LPC-based perceptual speech-coding algorithm with auditory masking that achieved a significant data compression ratio for its time.<ref name="Schroeder2014"/> IEEE's refereed ''Journal on Selected Areas in Communications'' reported on a wide variety of (mostly perceptual) audio compression algorithms in 1988.<ref name="Voice Coding for Communications" /> The "Voice Coding for Communications" edition published in February 1988 reported on a wide range of established, working audio bit compression technologies,<ref name="Voice Coding for Communications" /> some of them using auditory masking as part of their fundamental design, and several showing real-time hardware implementations.
=== Development === The genesis of the MP3 technology is fully described in a paper from Professor Hans Musmann,<ref name="musmann">Genesis of the MP3 Audio Coding Standard in IEEE Transactions on Consumer Electronics, IEEE, Vol. 52, Nr. 3, pp. 1043–1049, August 2006</ref> who chaired the ISO MPEG Audio group for several years. In December 1988, MPEG called for an audio coding standard. In June 1989, 14 audio coding algorithms were submitted. Because of certain similarities between these coding proposals, they were clustered into four development groups. The first group was ASPEC, by Fraunhofer Gesellschaft, AT&T, CNET(France Telecom) and Thomson.<ref>{{Cite conference |last1=Brandenburg |first1=K. |last2=Herre |first2=J. |last3=Johnston |first3=J. D. |last4=Mahieux |first4=Y. |last5=Schroeder |first5=E. F. |date=1991 |title=ASPEC. Adaptive Spectral Perceptual Entropy Coding of high quality music signals |url=https://publica.fraunhofer.de/handle/publica/319261 |language=en |publisher=AES |conference=Audio Engineering Society}}</ref> The second group was MUSICAM, by Matsushita, CCETT, ITT and Philips. The third group was ATAC (ATRAC Coding), by Fujitsu, JVC, NEC and Sony. And the fourth group was SB-ADPCM, by NTT and BTRL.<ref name="musmann"/>
The immediate predecessors of MP3 were "Optimum Coding in the Frequency Domain" (OCF),<ref name="Brandenburg" /> and Perceptual Transform Coding (PXFM).<ref name="Johnston1988" /> These two codecs, along with block-switching contributions from Thomson-Brandt, were merged into a codec called ASPEC, which was submitted to MPEG and won the quality competition, but which was rejected as too complex to implement.{{citation needed|date=March 2026}} The first practical implementation of an audio perceptual coder (OCF) in hardware (Krasner's hardware was too cumbersome and slow for practical use), was an implementation of a psychoacoustic transform coder based on Motorola 56000 DSP chips.{{citation needed|date=March 2026}}
Another predecessor of the MP3 format and technology was the perceptual codec MUSICAM based on an integer arithmetics 32 sub-bands filter bank, driven by a psychoacoustic model. It was primarily designed for Digital Audio Broadcasting (digital radio) and digital TV, and its basic principles were disclosed to the scientific community by CCETT (France) and IRT (Germany) in Atlanta during an IEEE-ICASSP conference in 1991,<ref>Y.F. Dehery, et al. (1991) A MUSICAM source codec for Digital Audio Broadcasting and storage Proceedings IEEE-ICASSP 91 pages 3605–3608 May 1991</ref> after having worked on MUSICAM with Matsushita and Philips since 1989.<ref name="musmann"/>
This codec incorporated into a broadcasting system using COFDM modulation was demonstrated on air and in the field<ref>{{cite web |title=A DAB commentary from Alan Box, EZ communication and chairman NAB DAB task force |url=https://www.worldradiohistory.com/Archive-BC/BC-1991/BC-1991-04-15.pdf}}</ref> with Radio Canada and CRC Canada during the NAB show (Las Vegas) in 1991. The implementation of the audio part of this broadcasting system was based on a two-chip encoder (one for the subband transform, one for the psychoacoustic model designed by the team of G. Stoll (IRT Germany), later known as psychoacoustic model I) and a real-time decoder using one Motorola 56001 DSP chip running an integer arithmetics software designed by Y.F. Dehery's team (CCETT, France). The simplicity of the corresponding decoder together with the high audio quality of this codec using for the first time a 48 kHz sampling rate, a 20 bits/sample input format (the highest available sampling standard in 1991, compatible with the AES/EBU professional digital input studio standard) were the main reasons to later adopt the characteristics of MUSICAM as the basic features for an advanced digital music compression codec.
During the development of the MUSICAM encoding software, Stoll and Dehery's team made thorough use of a set of high-quality audio assessment material<ref>{{cite book | url = https://tech.ebu.ch/publications/sqamcd | title = EBU SQAM CD Sound Quality Assessment Material recordings for subjective tests | date = 2008-10-07 | access-date = 8 February 2017 | archive-date = 11 February 2017 | archive-url = https://web.archive.org/web/20170211162447/https://tech.ebu.ch/publications/sqamcd | url-status = live }}</ref> selected by a group of audio professionals from the European Broadcasting Union, and later used as a reference for the assessment of music compression codecs. The subband coding technique was found to be efficient, not only for the perceptual coding of high-quality sound materials but especially for the encoding of critical percussive sound materials (drums, triangle,...), due to the specific temporal masking effect of the MUSICAM sub-band filterbank (this advantage being a specific feature of short transform coding techniques).
As a doctoral student at Germany's University of Erlangen-Nuremberg, Karlheinz Brandenburg began working on digital music compression in the early 1980s, focusing on how people perceive music. He completed his doctoral work in 1989.<ref name="BusinessWeek_2007" /> MP3 is directly descended from OCF and PXFM, representing the outcome of the collaboration of Brandenburg — working as a postdoctoral researcher at AT&T-Bell Labs with James D. Johnston ("JJ") of AT&T-Bell Labs — with the Fraunhofer Institute for Integrated Circuits, Erlangen (where he worked with Bernhard Grill and four other researchers – "The Original Six"<ref>{{Cite book|title=How Music Got Free: The End of an Industry, the Turn of the Century, and the Patient Zero of Piracy|last=Witt|first=Stephen|publisher=Penguin Books|year=2016|isbn=978-0-14-310934-1|location=United States of America|page=13|quote=Brandenburg and Grill were joined by four other Fraunhofer researchers. Heinz Gerhauser oversaw the institute´s audio research group; Harald Popp was a hardware specialist; Ernst Eberlein was a signal processing expert; Jurgen Herre was another graduate student whose mathematical prowess rivaled Brandenburg´s own. In later years this group would refer to themselves as "the original six".}}</ref>), with relatively minor contributions from the MP2 branch of psychoacoustic sub-band coders. In 1990, Brandenburg became an assistant professor at Erlangen-Nuremberg. While there, he continued to work on music compression with scientists at the Fraunhofer Society's Heinrich Herz Institute. In 1993, he joined the staff of Fraunhofer IIS in Erlangen.<ref>{{Cite web |title=Karlheinz Brandenburg |url=https://www.tu-ilmenau.de/universitaet/fakultaeten/fakultaet-elektrotechnik-und-informationstechnik/profil/institute-und-fachgebiete/fachgebiet-elektronische-medientechnik/team/karlheinz-brandenburg |access-date=2025-08-10 |website=Technische Universität Ilmenau |language=de}}</ref><ref name="BusinessWeek_2007" /> An acapella version of the song "Tom's Diner" by Suzanne Vega was the first song used by Brandenburg to develop the MP3 format. It was used as a benchmark to see how well MP3's compression algorithm handled the human voice. Brandenburg adopted the song for testing purposes, listening to it again and again each time he refined the compression algorithm, making sure it did not adversely affect the reproduction of Vega's voice.<ref name="Sterne2012_Vega" /> Accordingly, he dubbed Vega the "Mother of MP3".<ref name="motherofmp3" /> Instrumental music had been easier to compress, but Vega's voice sounded unnatural in early versions of the format. Brandenburg eventually met Vega and heard Tom's Diner performed live.
=== Standardization === In 1991, two available proposals were assessed for an MPEG audio standard: MUSICAM (<u>M</u>asking pattern adapted <u>U</u>niversal <u>S</u>ubband <u>I</u>ntegrated <u>C</u>oding <u>A</u>nd <u>M</u>ultiplexing) and ASPEC (<u>A</u>daptive <u>S</u>pectral <u>P</u>erceptual <u>E</u>ntropy <u>C</u>oding). The MUSICAM technique, proposed by Philips (Netherlands), CCETT (France), the Institute for Broadcast Technology (Germany), and Matsushita (Japan),<ref>Digital Video and Audio Broadcasting Technology: A Practical Engineering Guide (Signals and Communication Technology) {{ISBN|3-540-76357-0}} p. 144: "In the year 1988, the MASCAM method was developed at the Institut für Rundfunktechnik (IRT) in Munich in preparation for the digital audio broadcasting (DAB) system. From MASCAM, the MUSICAM (masking pattern universal subband integrated coding and multiplexing) method was developed in 1989 in cooperation with CCETT, Philips and Matsushita."</ref> was chosen due to its simplicity and error robustness, as well as for its high level of computational efficiency.<ref name="santa-clara-1990" /> The MUSICAM format, based on sub-band coding, became the basis for the MPEG Audio compression format, incorporating, for example, its frame structure, header format, sample rates, etc.
While much of MUSICAM technology and ideas were incorporated into the definition of MPEG Audio Layer I and Layer II, the filter bank alone and the data structure based on 1152 samples framing (file format and byte-oriented stream) of MUSICAM remained in the Layer III (MP3) format, as part of the computationally inefficient hybrid filter bank. Under the chairmanship of Professor Musmann of the Leibniz University Hannover, the editing of the standard was delegated to Leon van de Kerkhof (Netherlands), Gerhard Stoll (Germany), and Yves-François Dehery (France), who worked on Layer I and Layer II. ASPEC was the joint proposal of AT&T Bell Laboratories, Thomson Consumer Electronics, Fraunhofer Society, and CNET.<ref name="Aspec" /> It provided the highest coding efficiency.
A working group consisting of van de Kerkhof, Stoll, Leonardo Chiariglione (CSELT VP for Media), Yves-François Dehery, Karlheinz Brandenburg (Germany) and James D. Johnston (United States) took ideas from ASPEC, integrated the filter bank from Layer II, added some of their ideas such as the joint stereo coding of MUSICAM and created the MP3 format, which was designed to achieve the same quality at {{nowrap|128 kbit/s}} as MP2 at {{nowrap|192 kbit/s}}.
The algorithms for MPEG-1 Audio Layer I, II and III were approved in 1991<ref name="cd-1991" /><ref name="neuron2-cd-1991" /> and finalized in 1992<ref name="dis-1992" /> as part of MPEG-1, the first standard suite by MPEG, which resulted in the international standard '''ISO/IEC 11172-3''' (a.k.a. ''MPEG-1 Audio'' or ''MPEG-1 Part 3''), published in 1993.<ref name = "11172-3" /> Files or data streams conforming to this standard must handle sample rates of 48k, 44100, and 32k and continue to be supported by current MP3 players and decoders. Thus the first generation of MP3 defined {{math|14 × 3 {{=}} 42}} interpretations of MP3 frame data structures and size layouts.
The compression efficiency of encoders is typically defined by the bit rate because the compression ratio depends on the bit depth and sampling rate of the input signal. Nevertheless, compression ratios are often published. They may use the compact disc (CD) parameters as references (44.1 kHz, 2 channels at 16 bits per channel or 2×16 bit), or sometimes the Digital Audio Tape (DAT) SP parameters (48 kHz, 2×16 bit). Compression ratios with this latter reference are higher, which demonstrates the problem with the use of the term ''compression ratio'' for lossy encoders.
Brandenburg used a CD recording of Suzanne Vega's song "Tom's Diner" to assess and refine the MP3 compression algorithm.<ref>{{cite web |title=The MP3: A History Of Innovation And Betrayal |url=https://www.npr.org/sections/therecord/2011/03/23/134622940/the-mp3-a-history-of-innovation-and-betrayal |website=NPR |access-date=3 August 2023 |date=2011-03-23 |archive-date=3 August 2023 |archive-url=https://web.archive.org/web/20230803092021/https://www.npr.org/sections/therecord/2011/03/23/134622940/the-mp3-a-history-of-innovation-and-betrayal |url-status=live }}</ref> This song was chosen because of its nearly monophonic nature and wide spectral content, making it easier to hear imperfections in the compression format during playbacks. This particular track has an interesting property in that the two channels are almost, but not completely, the same, leading to a case where Binaural Masking Level Depression causes spatial unmasking of noise artifacts unless the encoder properly recognizes the situation and applies corrections similar to those detailed in the MPEG-2 AAC psychoacoustic model. Some more critical audio excerpts (glockenspiel, triangle, accordion, etc.) were taken from the EBU V3/SQAM reference compact disc and have been used by professional sound engineers to assess the subjective quality of the MPEG Audio formats.{{citation needed|date=August 2023}}
=== Going public === A reference simulation software implementation, written in the C language and later known as ''ISO 11172-5'', was developed (in 1991–1996) by the members of the ISO MPEG Audio committee to produce bit-compliant MPEG Audio files (Layer 1, Layer 2, Layer 3). It was approved as a committee draft of the ISO/IEC technical report in March 1994 and printed as document CD 11172-5 in April 1994.<ref name="paris_press" /> It was approved as a draft technical report (DTR/DIS) in November 1994,<ref name="singapore_press" /> finalized in 1996 and published as international standard ISO/IEC TR 11172-5:1998 in 1998.<ref name="ISO/IEC TR 11172-5:1998" /> The reference software in C language was later published as a freely available ISO standard.<ref name="Software_Simulation.zip" /> Working in non-real time on several operating systems, it was able to demonstrate the first real-time hardware decoding (DSP based) of compressed audio. Some other real-time implementations of MPEG Audio encoders and decoders<ref>{{Cite book|title=A high-quality sound coding standard for broadcasting, telecommunications and multimedia systems.|last=Dehery |first=Yves-Francois|publisher=Elsevier Science BV |year=1994|isbn= 978-0-444-81580-4 |location=The Netherlands |pages=53–64|quote= This article refers to a Musicam (MPEG Audio Layer II) compressed digital audio workstation implemented on a microcomputer used not only as a professional editing station but also as a server on Ethernet for a compressed digital audio library, therefore anticipating the future MP3 on Internet }}</ref> were available for digital broadcasting (radio DAB, television DVB) towards consumer receivers and set-top boxes.
On 7 July 1994, the Fraunhofer Society released the first software MP3 encoder, called l3enc.<ref name="MP3_Todays_Technology" /> The filename extension ''.mp3'' was chosen by the Fraunhofer team on 14 July 1995 (previously, the files had been named ''.bit'').<ref>{{Cite web |title=Timeline |url=https://www.mp3-history.com/en/timeline.html |access-date=2025-08-22 |website=Fraunhofer Institute for Integrated Circuits IIS |language=en}}</ref><ref name="mp3-name" /> With the first real-time software MP3 player WinPlay3 (released 9 September 1995) many people were able to encode and play back MP3 files on their PCs. Because of the relatively small hard drives of the era (≈500–1000 MB) lossy compression was essential to store multiple albums' worth of music on a home computer as full recordings (as opposed to MIDI notation, or tracker files which combined notation with short recordings of instruments playing single notes).
==== Internet spreading ==== A hacker nicknamed SoloH found the source code of the "dist10" MPEG reference implementation on the servers of the University of Erlangen shortly after the release. He integrated it within a graphical interface, enabling easy conversion from CD or WAV files, and spread it on the internet. This software started the widespread CD ripping and digital music distribution as MP3 over the internet.<ref>{{cite web |url-status=live |url=https://www.theatlantic.com/magazine/archive/2000/09/the-heavenly-jukebox/305141/ |archive-url=https://web.archive.org/web/20130430043648/https://www.theatlantic.com/magazine/archive/2000/09/the-heavenly-jukebox/305141/ |archive-date=30 April 2013 |website= The Atlantic |quote=To show industries how to use the codec, MPEG cobbled together a free sample program that converted music into MP3 files. The demonstration software created poor-quality sound, and Fraunhofer did not intend that it be used. The software's "source code"—its underlying instructions—was stored on an easily accessible computer at the University of Erlangen, from which it was downloaded by one SoloH, a hacker in the Netherlands (and, one assumes, a Star Wars fan). SoloH revamped the source code to produce software that converted compact-disc tracks into music files of acceptable quality. |url-access=subscription |title=The Heavenly Jukebox |first1=Charles C. |last1=Mann |date=September 2000 }}</ref><ref>''[https://books.google.com/books?id=3M2hAgAAQBAJ&dq=SoloH+mp3+source+code&pg=PT75 Pop Idols and Pirates: Mechanisms of Consumption and the Global Circulation of Popular Music]'' by Charles Fairchild. {{Webarchive|url=https://web.archive.org/web/20231015095150/https://books.google.com/books?id=3M2hAgAAQBAJ&dq=SoloH+mp3+source+code&pg=PT75 |date=15 October 2023 }}.</ref><ref>[http://ijoc.org/index.php/ijoc/article/viewFile/1765/989 Technologies of Piracy? – Exploring the Interplay Between Commercialism and Idealism in the Development of MP3 and DivX] {{Webarchive|url=https://web.archive.org/web/20200919101723/https://ijoc.org/index.php/ijoc/article/viewFile/1765/989 |date=19 September 2020 }} by HENDRIK STORSTEIN SPILKER, SVEIN HÖIER, page 2072</ref><ref>[https://web.archive.org/web/20170103170919/http://www.euronet.nl/~soloh/mpegEnc/ www.euronet.nl/~soloh/mpegEnc/] (Archive.org)</ref>
=== Further versions ===
{| class="wikitable sortable" |+MPEG Audio Layer III versions |- ! Version ! International Standard{{ref label|mp3standard|*|}} ! First edition public release date ! Latest edition public release date |- | MPEG-1 Audio Layer III | [https://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=22412 ISO/IEC 11172-3] {{Webarchive|url=https://web.archive.org/web/20120528230220/http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=22412 |date=28 May 2012 }} (MPEG-1 Part 3)<ref name="11172-3" /><ref name="neuron2-cd-1991" /> | 1993 | |- | MPEG-2 Audio Layer III | [https://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=26797 ISO/IEC 13818-3] {{Webarchive|url=https://web.archive.org/web/20110511043216/http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=26797 |date=11 May 2011 }} (MPEG-2 Part 3)<ref name="13818-3" /><ref name="mp3tech-iso13818-3" /> | 1995 | 1998 |- | MPEG-2.5 Audio Layer III | nonstandard, Fraunhofer proprietary<ref name="MPEG-2.5" /><ref name="MPEG-2.5-2" /> |2000 |2008 |} {{refbegin}} {{note label|mp3standard|*|}}The ISO standard ISO/IEC 11172-3 (a.k.a. MPEG-1 Audio) defined three formats: the MPEG-1 Audio Layer I, Layer II and Layer III. The ISO standard ISO/IEC 13818-3 (a.k.a. MPEG-2 Audio) defined an extended version of MPEG-1 Audio: MPEG-2 Audio Layer I, Layer II, and Layer III. MPEG-2 Audio (MPEG-2 Part 3) should not be confused with MPEG-2 AAC (MPEG-2 Part 7 – ISO/IEC 13818-7).<ref name="mpeg-audio-faq-bc" /> {{refend}}
==== MPEG-2 ==== Further work on MPEG audio<ref name="sydney1993" /> was finalized in 1994 as part of the second suite of MPEG standards, MPEG-2, more formally known as international standard '''ISO/IEC 13818-3''' (a.k.a. ''MPEG-2 Part 3'' or backward compatible ''MPEG-2 Audio'' or ''MPEG-2 Audio BC''<ref name="mpeg-audio-faq-bc" />), originally published in 1995.<ref name="13818-3" /><ref name="Brandenburg1997" /> MPEG-2 Part 3 (ISO/IEC 13818-3) defined 42 additional bit rates and sample rates for MPEG-1 Audio Layer I, II and III. The new sampling rates are exactly half that of those originally defined in MPEG-1 Audio. This reduction in sampling rates serves to cut the available frequency fidelity in half while likewise cutting the bit rate by 50%. MPEG-2 Part 3 also enhanced MPEG-1's audio by allowing the coding of audio programs with more than two channels, up to 5.1 multichannel, even though to this date no encoder is known to have used this feature.<ref name="sydney1993" />
==== MPEG-2.5 ==== A third generation of "MP3" style data streams (files) extended the ''MPEG-2'' ideas and implementation but was named ''MPEG-2.5'' audio since MPEG-3 already had a different meaning. This extension was developed at Fraunhofer IIS by reducing the frame sync field in the MP3 header from 12 to 11 bits. As in the transition from MPEG-1 to MPEG-2, MPEG-2.5 adds additional sampling rates exactly half of those available using MPEG-2. It thus widens the scope of MP3 to include human speech and other applications yet requires only 25% of the bandwidth (frequency reproduction) possible using MPEG-1 sampling rates. While not an ISO-recognized standard, MPEG-2.5 is widely supported by a majority of digital audio players as well as computer software-based MP3 encoders (LAME), decoders (FFmpeg) and players (MPC) adding {{math|3 × 8 {{=}} 24}} additional MP3 frame types. Each generation of MP3 thus supports 3 sampling rates exactly half that of the previous generation for a total of 9 variations of MP3 format files. The sample rate comparison table between MPEG-1, 2, and 2.5 is given later in the article.<ref name="MPEG-2.5" /><ref name="MPEG-2.5-2" /> MPEG-2.5 is supported by LAME (since 2000), Media Player Classic (MPC), iTunes, and FFmpeg.
MPEG-2.5 was not developed by MPEG (see above) and was never approved as an international standard. MPEG-2.5 is thus an unofficial or proprietary extension to the MP3 format. It is nonetheless ubiquitous and especially advantageous for low-bit-rate human speech applications.
=== Internet distribution === In the second half of the 1990s, MP3 files began to spread on the Internet, often via underground pirated song networks. The first known experiment in Internet distribution was organized in the early 1990s by the Internet Underground Music Archive, better known by the acronym IUMA. After some experiments<ref>{{cite web | url = https://archive.org/details/iuma-archive&tab=about | title = About Internet Underground Music Archive }}</ref> using uncompressed audio files, this archive started to deliver on the native worldwide low-speed Internet some compressed MPEG Audio files using the MP2 (Layer II) format and later on used MP3 files when the standard was fully completed. The popularity of MP3s began to rise rapidly with the advent of Nullsoft's audio player Winamp, released in 1997, which still had in 2023 a community of 80 million active users.<ref>{{Cite web |last=Vainilavičius |first=Justinas |date=15 November 2023 |title=Winamp is back after revamp; nostalgia-inducing looks intact |url=https://cybernews.com/news/winamp-is-back-after-revamp-nostalgia-inducing-looks-intact/ |access-date=8 December 2023 |website=cybernews |archive-date=4 December 2023 |archive-url=https://web.archive.org/web/20231204111949/https://cybernews.com/news/winamp-is-back-after-revamp-nostalgia-inducing-looks-intact/ |url-status=live }}</ref> In 1998, Windows Media Player 5.2 and later added support for MP3 format, and the first portable solid-state digital audio player MPMan, developed by SaeHan Information Systems, which is headquartered in Seoul, South Korea, was released and the Rio PMP300 was sold afterward in 1998, despite legal suppression efforts by the RIAA.<ref name="seattlepi" />
In November 1997, the website mp3.com was offering thousands of MP3s created by independent artists for free.<ref name="seattlepi" /> The small size of MP3 files enabled widespread peer-to-peer file sharing of music ripped from CDs, which would have previously been nearly impossible. The first large peer-to-peer filesharing network, Napster, was launched in 1999. The ease of creating and sharing MP3s resulted in widespread copyright infringement. Major record companies argued that this free sharing of music reduced sales, and called it "music piracy". They reacted by pursuing lawsuits against Napster, which was eventually shut down and later sold, and against individual users who engaged in file sharing. Napster later returned as a legitimate music streaming service.<ref name="Giesler" />
Unauthorized MP3 file sharing continues on next-generation peer-to-peer networks. Authorized services, such as Amazon.com, Beatport, Bleep, eMusic, Juno Records, and the reincarnated Napster, sell unrestricted music in the MP3 format.
== Design ==
=== File structure === {{Panorama |image = File:Mp3filestructure.svg |height = 400 |alt = Diagram of the structure of an MP3 file |caption = Diagram of the structure of an MP3 file (MPEG version 2.5, not described here, changes the last bit of sync word to "0" as an indication, effectively moving one bit to the version field.<ref name="MPEG-2.5-2" />) }}
An MP3 file is made up of MP3 frames, which consist of a header and a data block. This sequence of frames is called an elementary stream. Due to the "bit reservoir", frames are not independent items and cannot usually be extracted on arbitrary frame boundaries. The MP3 Data blocks contain the (compressed) audio information in terms of frequencies and amplitudes. The diagram shows that the MP3 Header consists of a sync word, which is used to identify the beginning of a valid frame. This is followed by a bit indicating that this is the MPEG standard and two bits that indicate that layer 3 is used; hence MPEG-1 Audio Layer 3 or MP3. After this, the values will differ, depending on the MP3 file. ''ISO/IEC 11172-3'' defines the range of values for each section of the header along with the specification of the header. Most MP3 files today contain ID3 metadata, which precedes or follows the MP3 frames, as noted in the diagram. The data stream can contain an optional checksum.
Joint stereo is done only on a frame-to-frame basis.<ref name="Limitations"/>
=== Encoding and decoding === In short, MP3 compression works by reducing 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.<ref name="Jayant1993" /> The remaining audio information is then recorded in a space-efficient manner using MDCT and FFT algorithms.
The MP3 encoding algorithm is generally split into four parts. Part 1 divides the audio signal into smaller pieces, called frames, and an MDCT filter is then performed on the output. Part 2 passes the sample into a 1024-point fast Fourier transform (FFT), then the psychoacoustic model is applied and another MDCT filter is performed on the output. Part 3 quantifies and encodes each sample, known as noise allocation, which adjusts itself to meet the bit rate and sound masking requirements. Part 4 formats the bitstream, called an audio frame, which is made up of 4 parts, the header, error check, audio data, and ancillary data.<ref name="Guckert"/>
MP3 uses an overlapping MDCT structure. Each MPEG-1 MP3 frame is 1152 samples, divided into two granules of 576 samples. These 576 consecutive samples, initially in the time domain, are transformed in one block to 576 frequency-domain samples by MDCT.<ref>{{cite web |last=Taylor |first=Mark |date=June 2000 |title=LAME Technical FAQ |url=https://lame.sourceforge.io/tech-FAQ.txt |access-date=9 December 2023 |archive-date=8 December 2023 |archive-url=https://web.archive.org/web/20231208232048/https://lame.sourceforge.io/tech-FAQ.txt |url-status=live }}</ref> MP3 also allows the use of shorter blocks in a granule, down to a size of 192 samples; this feature is used when a transient is detected. Doing so limits the temporal spread of quantization noise accompanying the transient (see psychoacoustics). Frequency resolution is limited by the small long block window size, which decreases coding efficiency.<ref name="Limitations"/> Time resolution can be too low for highly transient signals and may cause smearing of percussive sounds.<ref name="Limitations" />
Due to the tree structure of the filter bank, pre-echo problems are made worse, as the combined impulse response of the two filter banks does not, and cannot, provide an optimum solution in time/frequency resolution.<ref name="Limitations"/> Additionally, the combining of the two filter banks' outputs creates aliasing problems that must be handled partially by the "aliasing compensation" stage; however, that creates excess energy to be coded in the frequency domain, thereby decreasing coding efficiency.<ref>{{Cite book|last=Liberman|first=Serbio|title=DSP – The Technology Behind Multimedia|language=English}}</ref>
Decoding, on the other hand, is carefully defined in the standard. Most decoders are "bitstream compliant", which means that the decompressed output that they produce from a given MP3 file will be the same, within a specified degree of rounding tolerance, as the output specified mathematically in the ISO/IEC high standard document (ISO/IEC 11172-3). Therefore, the comparison of decoders is usually based on how computationally efficient they are (i.e., how much memory or CPU time they use in the decoding process). Over time this concern has become less of an issue as CPU clock rates transitioned from MHz to GHz. Encoder/decoder overall delay is not defined, which means there is no official provision for gapless playback. However, some encoders such as LAME can attach additional metadata that will allow players that can handle it to deliver seamless playback.
=== Quality === When performing lossy audio encoding, such as creating an MP3 data stream, there is a trade-off between the amount of data generated and the sound quality of the results. The person generating an MP3 selects a bit rate, which specifies how many kilobits per second of audio is desired. The higher the bit rate, the larger the MP3 data stream will be, and, generally, the closer it will sound to the original recording. With too low a bit rate, compression artifacts (i.e., sounds that were not present in the original recording) may be audible in the reproduction. Some audio is hard to compress because of its randomness and sharp attacks. When this type of audio is compressed, artifacts such as ringing or pre-echo are usually heard. A sample of applause or a triangle instrument with a relatively low bit rate provides good examples of compression artifacts. Most subjective testings of perceptual codecs tend to avoid using these types of sound materials, however, the artifacts generated by percussive sounds are barely perceptible due to the specific temporal masking feature of the 32-sub-band filterbank of Layer II on which the format is based.
The MPEG-1 standard does not include a precise specification for an MP3 encoder but does provide examples of psychoacoustic models, rate loops, and the like in the non-normative part of the original standard.<ref name="mpeg1" /> When this was written, the suggested implementations were quite dated. Implementers of the standard were supposed to devise algorithms suitable for removing parts of the information from the audio input. As a result, many different MP3 encoders became available, each producing files of differing quality. Comparisons were widely available, so it was easy for a prospective user of an encoder to research the best choice. Some encoders that were proficient at encoding at higher bit rates (such as LAME) were not necessarily as good at lower bit rates.
Besides the bit rate of an encoded piece of audio, the quality of MP3-encoded sound also depends on the quality of the encoder algorithm as well as the complexity of the signal being encoded. As the MP3 standard allows quite a bit of freedom with encoding algorithms, different encoders do feature quite different quality, even with identical bit rates. As an example, in a public listening test featuring two early MP3 encoders set at about {{nowrap|128 kbit/s}},<ref name="Amorim" /> one scored 3.66 on a 1–5 scale, while the other scored only 2.22. Quality is dependent on the choice of encoder and encoding parameters.<ref name="listening-test-128-2006" />
This observation caused a revolution in audio encoding. Early on bit rate was the prime and only consideration. At the time MP3 files were of the very simplest type: they used the same bit rate for the entire file: this process is known as constant bit rate (CBR) encoding. Using a constant bit rate makes encoding simpler and less CPU-intensive. However, it is also possible to optimize the size of the file by creating files where the bit rate changes throughout the file. These are known as variable bit rate. The bit reservoir and VBR encoding were part of the original MPEG-1 standard. The concept behind them is that, in any piece of audio, some sections are easier to compress, such as silence or music containing only a few tones, while others will be more difficult to compress. So, the overall quality of the file may be increased by using a lower bit rate for the less complex passages and a higher one for the more complex parts. With some advanced MP3 encoders, it is possible to specify a given quality, and the encoder will adjust the bit rate accordingly. Users that desire a particular "quality setting" that is transparent to their ears can use this value when encoding all of their music, and generally speaking not need to worry about performing personal listening tests on each piece of music to determine the correct bit rate.
Perceived quality can be influenced by the listening environment (ambient noise), listener attention, listener training, and in most cases by listener audio equipment (such as sound cards, speakers, and headphones). Furthermore, sufficient quality may be achieved by a lesser quality setting for lectures and human speech applications and reduces encoding time and complexity. A test given to new students by Stanford University Music Professor Jonathan Berger showed that student preference for MP3-quality music has risen each year. Berger said the students seem to prefer the 'sizzle' sounds that MP3s bring to music.<ref name="Dougherty"/>
An in-depth study of MP3 audio quality, sound artist and composer Ryan Maguire's project "The Ghost in the MP3" isolates the sounds lost during MP3 compression. In 2015, he released the track "moDernisT" (an anagram of "Tom's Diner"), composed exclusively from the sounds deleted during MP3 compression of the song "Tom's Diner",<ref name="noisey" /><ref name="schroeder2015" /><ref name="hull2015" /> the track originally used in the formulation of the MP3 standard. A detailed account of the techniques used to isolate the sounds deleted during MP3 compression, along with the conceptual motivation for the project, was published in the 2014 Proceedings of the International Computer Music Conference.<ref name="Maguire2014" />
=== Bit rate and sampling rates === {{more citations needed section|date=July 2020}} {| class="wikitable floatright" style="max-width: 22em; font-size: 85%;" |+MPEG Audio Layer III<br />available bit rates {{nowrap|(kbit/s)}}<ref name="neuron2-cd-1991" /><ref name="MPEG-2.5" /><ref name="MPEG-2.5-2" /><ref name="mp3tech-iso13818-3" /><ref>{{cite web |title=Guide to command line options (in CVS) |url=https://lame.cvs.sourceforge.net/viewvc/lame/lame/USAGE |url-status=dead |archive-url=https://web.archive.org/web/20130408110355/http://lame.cvs.sourceforge.net/viewvc/lame/lame/USAGE |archive-date=8 April 2013 |access-date=4 August 2010}}</ref> |- ! MPEG-1<br />Audio Layer III ! MPEG-2<br />Audio Layer III ! MPEG-2.5<br />Audio Layer III |- | – | 8 | 8 |- | – | 16 | 16 |- | – | 24 | 24 |- | 32 | 32 | 32 |- | 40 | 40 | 40 |- | 48 | 48 | 48 |- | 56 | 56 | 56 |- | 64 | 64 | 64 |- | 80 | 80 | – |- | 96 | 96 | – |- | 112 | 112 | – |- | 128 | 128 | – |- | –
| 144 | – |- | 160 | 160 | – |- | 192 | – | – |- | 224 | – | – |- | 256 | – | – |- | 320 | – | – |}
{| class="wikitable floatright" style="max-width: 22em; font-size: 85%;" |+Supported sampling rates<br />by MPEG Audio Format<ref name="neuron2-cd-1991" /><ref name="MPEG-2.5" /><ref name="MPEG-2.5-2" /><ref name="mp3tech-iso13818-3" /> |- ! MPEG-1<br />Audio Layer III ! MPEG-2<br />Audio Layer III ! MPEG-2.5<br />Audio Layer III |- | – | – | 8 kHz |- | – | – | 11.025 kHz |- | – | – | 12 kHz |- | – | 16 kHz | – |- | – | 22.05 kHz | – |- | – | 24 kHz | – |- | 32 kHz | – | – |- | 44.1 kHz | – | – |- | 48 kHz | – | – |} ''Bit rate'', technically ''data rate'', usually measured in ''bits per second'', is linked, when encoding audio data, to the ''sample size'' (the number of bits per audio sample) and sampling rate: CD audio is encoded with simple pulse-code modulation using 16-bit samples, {{val|44100}} of them per second, for each of two channels (left and right). So, multiplying {{val|44100|u=samples per second}} by {{val|16|u=bits per sample}} by {{val|2|u=channels}} gives {{val|1411200|u=bits per second}}—the data rate of uncompressed CD digital audio. MP3 was designed to encode this {{val|1411|u=kbit/s}} raw data at {{val|320|u=kbit/s}} or less. If less complex passages are detected by the MP3 algorithms then lower bit rates may be employed.
As shown in these two tables:
* 14 selected bit rates are allowed in MPEG-1 Audio Layer III standard: 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256 and {{nowrap|320 kbit/s}}, along with the 3 highest available sampling rates of 32, 44.1 and 48 kHz.<ref name="MPEG-2.5-2" /> * MPEG-2 Audio Layer III also allows 14 globally lower bit rates of 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, {{nowrap|160 kbit/s}} with sampling rates of 16, 22.05 and 24 kHz which are exactly half that of MPEG-1.<ref name="MPEG-2.5-2" /> * MPEG-2.5 Audio Layer III frames are limited to only 8 bit rates of 8, 16, 24, 32, 40, 48, 56 and {{nowrap|64 kbit/s}} with 3 even lower sampling rates of 8, 11.025, and 12 kHz.{{Citation needed|reason=Based on results from the LAME encoder, these do seem to be the actual bit rates supported by MPEG-2.5, but official documents claim MPEG-2.5 has the same possible bit rates as MPEG-2. Answer: Bitrate switching implies VBR so, it is not CBR anymore. When MPEG-2 frames are needed instead of the smaller 2.5 frames, the former are generated. Can we find a source that mentions this limitation?|date=December 2013}}.
Earlier systems also lack fast forwarding and rewinding playback controls on MP3.<ref>{{cite web |quote=Search – locating a desired position on thedisc (audio CD only) |url=http://resources.jvc.com/Resources/00/00/95/lvt1213-001b.pdf |archive-url=https://web.archive.org/web/20200820112149/http://resources.jvc.com/Resources/00/00/95/lvt1213-001b.pdf |archive-date=20 August 2020 |language=mul |page=14 |title=JVC RC-EX30 operation manual |date=2004 |access-date=20 August 2020 |url-status=dead }} (2004 boombox)</ref><ref>{{cite web |url=https://www.sharp.co.uk/cps/rde/xbcr/documents/documents/om/13_dvd/DVRW250H_OM_GB.pdf |quote=• Fast forward and review playback does not work with a MP3/WMA/JPEG-CD. |page=33 |language=en-gb |title=DV-RW250H Operation-Manual GB |date=2004 |access-date=20 August 2020 |archive-date=20 August 2020 |archive-url=https://web.archive.org/web/20200820113949/https://www.sharp.co.uk/cps/rde/xbcr/documents/documents/om/13_dvd/DVRW250H_OM_GB.pdf |url-status=live }}</ref>
MPEG-1 frames contain the most detail in {{nowrap|320 kbit/s}} mode, the highest allowable bit rate setting,<ref>{{cite web |title=Sound Quality Comparison of Hi-Res Audio vs. CD vs. MP3 |url=https://www.sony.com/electronics/hi-res-audio-mp3-cd-sound-quality-comparison |website=www.sony.com |publisher=Sony |access-date=11 August 2020 |language=en |archive-date=14 September 2020 |archive-url=https://web.archive.org/web/20200914005253/https://www.sony.com/electronics/hi-res-audio-mp3-cd-sound-quality-comparison |url-status=live }}</ref> with silence and simple tones still requiring {{nowrap|32 kbit/s}}. MPEG-2 frames can capture up to 12 kHz sound reproductions needed up to {{nowrap|160 kbit/s}}.
A sample rate of 44.1 kHz is commonly used for music reproduction because this is also used for CD audio, the main source used for creating MP3 files. A great variety of bit rates are used on the Internet. A bit rate of {{nowrap|128 kbit/s}} is commonly used,<ref name="Woon-Seng" /> at a compression ratio of 11:1, offering adequate audio quality in a relatively small space. As Internet bandwidth availability and hard drive sizes have increased, higher bit rates up to {{nowrap|320 kbit/s}} are widespread. Uncompressed audio as stored on an audio-CD has a bit rate of {{nowrap|1,411.2 kbit/s}}, (16 bit/sample × 44,100 samples/second × 2 channels / 1,000 bits/kilobit), so the bit rates 128, 160, and {{nowrap|192 kbit/s}} represent compression ratios of approximately 11:1, 9:1 and 7:1 respectively.
Non-standard bit rates up to {{nowrap|640 kbit/s}} can be achieved with the LAME encoder and the free format option, although few MP3 players can play those files. According to the ISO standard, decoders are only required to be able to decode streams up to {{nowrap|320 kbit/s}}.<ref name="Bouvigne" /><ref>{{Cite web|title=lame(1): create mp3 audio files – Linux man page|url=https://linux.die.net/man/1/lame|access-date=2020-08-22|website=linux.die.net|archive-date=22 August 2020|archive-url=https://web.archive.org/web/20200822103430/https://linux.die.net/man/1/lame|url-status=live}}</ref><ref>{{Cite web|title=Linux Manpages Online – man.cx manual pages|url=https://man.cx/lame|access-date=2020-08-22|website=man.cx|archive-date=22 August 2020|archive-url=https://web.archive.org/web/20200822103425/https://man.cx/lame|url-status=live}}</ref> Early MPEG Layer III encoders used what is now called constant bit rate (CBR). The software was only able to use a uniform bit rate on all frames in an MP3 file. Later more sophisticated MP3 encoders were able to use the bit reservoir to target an average bit rate selecting the encoding rate for each frame based on the complexity of the sound in that portion of the recording.
A more sophisticated MP3 encoder can produce variable bit rate audio. MPEG audio may use bit rate switching on a per-frame basis, but only layer III decoders must support it.<ref name="MPEG-2.5-2" /><ref name="LAME_GPSYCHO" /><ref name="TwoLAME" /><ref name="MPEG-1 and MPEG-2 BC" /> VBR is used when the goal is to achieve a fixed level of quality. The final file size of a VBR encoding is less predictable than with constant bit rate. Average bit rate is a type of VBR implemented as a compromise between the two: the bit rate is allowed to vary for more consistent quality, but is controlled to remain near an average value chosen by the user, for predictable file sizes. Although an MP3 decoder must support VBR to be standards compliant, historically some decoders have bugs with VBR decoding, particularly before VBR encoders became widespread.
Layer III audio can also use a "bit reservoir", a partially full frame's ability to hold part of the next frame's audio data, allowing temporary changes in effective bit rate, even in a constant bit rate stream.<ref name="MPEG-2.5-2" /><ref name="LAME_GPSYCHO" /> Internal handling of the bit reservoir increases encoding delay.<ref>{{cite web |title=A guideline to audio codec delay |url=https://www.iis.fraunhofer.de/content/dam/iis/de/doc/ame/conference/AES-116-Convention_guideline-to-audio-codec-delay_AES116.pdf |website=www.iis.fraunhofer.de |publisher=Fraunhofer Institute |access-date=11 May 2026}}</ref>There is no scale factor band 21 (sfb21) for frequencies above approx 16 kHz, forcing the encoder to choose between less accurate representation in band 21 or less efficient storage in all bands below band 21, the latter resulting in wasted bit rate in VBR encoding.<ref name="LAME Y" />
=== Ancillary data === The ancillary data field can be used to store user-defined data. The ancillary data is optional and the number of bits available is not explicitly given. The ancillary data is located after the Huffman code bits and ranges to where the next frame's main_data_begin points to. Encoder mp3PRO used ancillary data to encode extra information which could improve audio quality when decoded with its algorithm.
=== Metadata === {{main|ID3|APEv2 tag}}
A "tag" in an audio file is a section of the file that contains metadata such as the title, artist, album, track number, or other information about the file's contents. The MP3 standards do not define tag formats for MP3 files, nor is there a standard container format that would support metadata and obviate the need for tags. However, several ''de facto'' standards for tag formats exist. As of 2010, the most widespread are ID3v1 and ID3v2, and the more recently introduced APEv2. These tags are normally embedded at the beginning or end of MP3 files, separate from the actual MP3 frame data. MP3 decoders either extract information from the tags or just treat them as ignorable, non-MP3 junk data.
Playing and editing software often contains tag editing functionality, but there are also tag editor applications dedicated to the purpose. Aside from metadata about the audio content, tags may also be used for DRM.<ref name="Rae" /> ReplayGain is a standard for measuring and storing the loudness of an MP3 file (audio normalization) in its metadata tag, enabling a ReplayGain-compliant player to automatically adjust the overall playback volume for each file. MP3Gain may be used to reversibly modify files based on ReplayGain measurements so that adjusted playback can be achieved on players without ReplayGain capability.
== {{anchor|Licensing and patent issues}}Licensing, ownership, and legislation ==
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.<ref name="Patel" /><ref name="mpegfa31.txt" /> 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.<ref name="big-list" /> 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 {{US patent|5812672}}, which had a PCT filing in October 1992, expired.<ref name="Cogliati" /><ref name="US5812672" /><ref name="Patent expiration" /> 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 {{US patent|6009399}}, held<ref>{{Cite web|url=https://patents.google.com/patent/US6009399/en|title=Method and apparatus for encoding digital signals employing bit allocation using combinations of different threshold models to achieve desired bit rates|access-date=21 January 2023|archive-date=21 January 2023|archive-url=https://web.archive.org/web/20230121152351/https://patents.google.com/patent/US6009399/en|url-status=live}}</ref> and administered by Technicolor,<ref>{{cite web|url=http://mp3licensing.com/patents/index.html|title=mp3licensing.com – Patents|work=mp3licensing.com|access-date=10 May 2008|archive-date=9 May 2008|archive-url=https://web.archive.org/web/20080509182032/http://www.mp3licensing.com/patents/index.html|url-status=live}}</ref> 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.<ref>{{Cite web| url=https://fedoramagazine.org/full-mp3-support-coming-soon-to-fedora/| title=Full MP3 support coming soon to Fedora| date=2017-05-05| access-date=17 June 2017| archive-date=27 June 2017| archive-url=https://web.archive.org/web/20170627062915/https://fedoramagazine.org/full-MP3-support-coming-soon-to-fedora/| url-status=live}}</ref>
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.<ref name="ffii" /> Technicolor had been actively enforcing these patents.<ref name="Technicolor" /> MP3 license revenues from Technicolor's administration generated about €100 million for the Fraunhofer Society in 2005.<ref name="Kistenfeger" /> 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."<ref name="chillingeffects" /> 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.<ref>{{cite web | url = http://www.sisvel.com/licensing-programs/audio-and-video-coding-decoding/mpeg-audio/introduction | title = SISVEL's MPEG Audio licensing programme | access-date = 8 February 2017 | archive-date = 11 February 2017 | archive-url = https://web.archive.org/web/20170211075921/http://www.sisvel.com/licensing-programs/audio-and-video-coding-decoding/mpeg-audio/introduction | url-status = live }}</ref> They, along with its United States subsidiary Audio MPEG, Inc. previously sued Thomson for patent infringement on MP3 technology,<ref name="ZDNet India" /> 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.<ref name="SISVEL" /> Except for three patents, the US patents administered by Sisvel<ref>{{cite web |title=US MPEG Audio patents |url=https://www.sisvel.com/MPEG_Audio/US_Patents.pdf |url-status=dead |archive-url=https://web.archive.org/web/20161027094014/http://www.sisvel.com/MPEG_Audio/US_Patents.pdf |archive-date=27 October 2016 |access-date=7 April 2017 |publisher=Sisvel}}</ref> had all expired in 2015. The three exceptions are: {{US patent|5878080}}, expired February 2017; {{US patent|5850456}}, expired February 2017; and {{US patent|5960037}}, expired 9 April 2017. As of around the first quarter of 2023, Sisvel's licensing program has become a legacy.<ref>{{cite web |title=Licensing Programs – Legacy programs |url=https://www.sisvel.com/licensing-programs/legacy-programs |website=www.sisvel.com |access-date=15 September 2023 |archive-url=https://web.archive.org/web/20230219230637/https://www.sisvel.com/licensing-programs/legacy-programs |archive-date=February 19, 2023 |language=en-gb}}</ref>
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,<ref name="SanDisk MP3 seizure" /> 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.<ref name="Patent Wild West" /> 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.<ref name="law360" /><ref name="Kelly" />
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.<ref name="MP3 payout" /> 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.<ref name="Microsoft wins reversal" /> That defense judgment was upheld on appeal in 2008.<ref name="Alcatel-Lucent" />
== Alternative technologies == {{Main|List of codecs}} {{listen|filename=Test ogg mp3 48kbps.wav|title=Comparison between MP3 and Vorbis|description=The first is uncompressed WAV file. The second is a Vorbis file encoded at {{nowrap|48 kbit/s}}, and third is an MP3 encoded at {{nowrap|48 kbit/s}} using LAME.}}
Other lossy formats exist. Among these, Advanced Audio Coding (AAC) is the most widely used, and was designed to be the successor to MP3. There also exist other lossy formats such as mp3PRO and MP2. They are members of the same technological family as MP3 and depend on roughly similar psychoacoustic models and MDCT algorithms. Whereas MP3 uses a hybrid coding approach that is part MDCT and part FFT, AAC is purely MDCT, significantly improving compression efficiency.<ref name="brandenburg"/> Many of the basic patents underlying these formats are held by Fraunhofer Society, Alcatel-Lucent, Thomson Consumer Electronics,<ref name="brandenburg" /> Bell, Dolby, LG Electronics, NEC, NTT Docomo, Panasonic, Sony,<ref>{{cite web |title=Via Licensing Announces Updated AAC Joint Patent License |url=https://www.businesswire.com/news/home/20090105005026/en/Licensing-Announces-Updated-AAC-Joint-Patent-License |website=Business Wire |access-date=18 June 2019 |date=5 January 2009 |archive-date=18 June 2019 |archive-url=https://web.archive.org/web/20190618122721/https://www.businesswire.com/news/home/20090105005026/en/Licensing-Announces-Updated-AAC-Joint-Patent-License |url-status=live }}</ref> ETRI, JVC Kenwood, Philips, Microsoft, and NTT.<ref>{{cite web |title=AAC Licensors |url=http://www.via-corp.com/us/en/licensing/aac/licensors.html |website=Via Corp |access-date=6 July 2019 |archive-date=28 June 2019 |archive-url=https://web.archive.org/web/20190628173314/http://www.via-corp.com/us/en/licensing/aac/licensors.html }}</ref>
Microsoft created and promoted their own competing standard, Windows Media Audio (WMA) with the claim that it is better than MP3.<ref>{{cite web |last1=Hornung |first1=Armin |last2=Krivosheev |first2=Gleb |last3=Singh |first3=Noor |last4=Bilger |first4=Jeff |title=Standards Wars |url=https://courses.cs.washington.edu/courses/csep590a/06au/projects/standards-wars.pdf |website=University of Washington CSEP590A |date=Autumn 2006 |access-date=12 August 2025}}</ref> When the digital audio player market was taking off, MP3 was widely adopted as the standard hence the popular name "MP3 player". Sony was an exception and used their own ATRAC codec taken from their MiniDisc format, which Sony claimed was better.<ref>{{Cite news|url=https://www.nytimes.com/1999/09/30/technology/news-watch-new-player-from-sony-will-give-a-nod-to-mp3.html|title=NEWS WATCH; New Player from Sony Will Give a Nod to MP3|newspaper=The New York Times|date=30 September 1999|last1=Marriott|first1=Michel|access-date=24 September 2020|archive-date=3 July 2021|archive-url=https://web.archive.org/web/20210703065644/https://www.nytimes.com/1999/09/30/technology/news-watch-new-player-from-sony-will-give-a-nod-to-mp3.html|url-status=live}}</ref> Following criticism and lower than expected Walkman sales, in 2004 Sony for the first time introduced native MP3 support to its Walkman players.<ref>{{Cite web|url=https://www.cnet.com/reviews/sony-nw-e100-review/|title=Sony NW-E105 Network Walkman|access-date=24 September 2020|archive-date=31 October 2020|archive-url=https://web.archive.org/web/20201031221331/https://www.cnet.com/reviews/sony-nw-e100-review/|url-status=live}}</ref>
There are also open compression formats like Opus and Vorbis (OGG) that are available free of charge and without any known patent restrictions.<ref name="big-list" />
Besides lossy compression methods, lossless formats are a significant alternative to MP3 because they provide unaltered audio content, though with an increased file size compared to lossy compression. Lossless formats include FLAC (Free Lossless Audio Codec), Apple Lossless and many others.
==See also== *MP3 Surround *Windows Media Audio (WMA) *Comparison of audio coding formats
== References == <references>
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Audio Engineering Society | volume = 45 | issue = 1/2 | pages = 4–21 | date = February 1997 | access-date = 30 June 2008 | archive-date = 17 April 2009 | archive-url = https://web.archive.org/web/20090417030540/http://www.aes.org/e-lib/browse.cfm?elib=7871 | url-status = live }}</ref> <ref name="MPEG-2.5">{{ cite web | url = http://www.iis.fraunhofer.de/EN/bf/amm/projects/mp3/index.jsp | archive-url = https://web.archive.org/web/20080124200925/http://www.iis.fraunhofer.de/EN/bf/amm/projects/mp3/index.jsp | archive-date = 24 January 2008 | publisher = Fraunhofer IIS | title = MP3 technical details (MPEG-2 and MPEG-2.5) | quote = "MPEG-2.5" is the name of a proprietary extension developed by Fraunhofer IIS. It enables MP3 to work satisfactorily at very low bitrates and introduces the additional sampling rates 8 kHz, 11.025 kHz and 12 kHz. | date = September 2007 }}</ref> <ref name="MPEG-2.5-2">{{cite web | first = Predrag | last = Supurovic | title = MPEG Audio Frame Header | date = 22 December 1999 | url = https://www.datavoyage.com/mpgscript/mpeghdr.htm | access-date = 29 May 2009 | archive-date = 7 September 2008 | archive-url = https://web.archive.org/web/20080907114653/http://www.datavoyage.com/mpgscript/mpeghdr.htm | url-status = live }}</ref> <ref name="mp3tech-iso13818-3">{{cite web | url = http://www.mp3-tech.org/programmer/docs/iso13818-3.zip | format = ZIP | title = ISO/IEC 13818-3:1994(E) – Information Technology — Generic Coding of Moving Pictures and Associated Audio: Audio | date = 11 November 1994 | access-date = 4 August 2010 | archive-date = 13 June 2010 | archive-url = https://web.archive.org/web/20100613060642/http://mp3-tech.org/programmer/docs/iso13818-3.zip | url-status = live }}</ref> <ref name="motherofmp3">{{Cite web | url=https://www.suzannevega.com/bio | work=The Official Community of Suzanne Vega | title=Suzanne Vega {{!}} Bio | access-date=2022-01-17 | archive-date=18 January 2022 | archive-url=https://web.archive.org/web/20220118183253/https://www.suzannevega.com/bio | url-status=live }}</ref> <ref name="paris_press">{{ cite web | url = http://mpeg.chiariglione.org/meetings/paris94/paris_press.htm | title = Approved at 26th meeting (Paris) | author = MPEG | date = 25 March 1994 | access-date = 5 August 2010 | archive-url = https://web.archive.org/web/20100726103705/http://mpeg.chiariglione.org/meetings/paris94/paris_press.htm | archive-date = 26 July 2010 }}</ref> <ref name="singapore_press">{{ cite web | url = http://mpeg.chiariglione.org/meetings/singapore94/singapore_press.htm | title = Approved at 29th meeting | date = 11 November 1994 | author = MPEG | access-date = 5 August 2010 | archive-url = https://web.archive.org/web/20100808100029/http://mpeg.chiariglione.org/meetings/singapore94/singapore_press.htm | archive-date = 8 August 2010 }}</ref> <ref name="ISO/IEC TR 11172-5:1998">{{cite web | url = http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=25029 | title = ISO/IEC TR 11172-5:1998 – Information technology – Coding of moving pictures and associated audio for digital storage media at up to about 1,5 Mbit/s – Part 5: Software simulation | author = ISO | access-date = 5 August 2010 | archive-date = 11 May 2011 | archive-url = https://web.archive.org/web/20110511043221/http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=25029 | url-status = live }}</ref> <ref name="Software_Simulation.zip">{{cite web | url = http://standards.iso.org/ittf/PubliclyAvailableStandards/c025029_ISO_IEC_TR_11172-5_1998(E)_Software_Simulation.zip | title = ISO/IEC TR 11172-5:1998 – Information technology – Coding of moving pictures and associated audio for digital storage media at up to about 1,5 Mbit/s – Part 5: Software simulation (Reference Software) | format = ZIP | access-date = 5 August 2010 | archive-date = 30 December 2006 | archive-url = https://web.archive.org/web/20061230121352/http://standards.iso.org/ittf/PubliclyAvailableStandards/c025029_ISO_IEC_TR_11172-5_1998(E)_Software_Simulation.zip | url-status = live }}</ref> <ref name="MP3_Todays_Technology">{{ cite web | title = MP3 Today's Technology | work = Lots of Informative Information about Music | year = 2005 | url = http://www.513rocks.com/MP3_Todays_Technology_158.shtml |archive-url=https://web.archive.org/web/20080704065939/http://513rocks.com/MP3_Todays_Technology_158.shtml |archive-date=4 July 2008 |access-date=15 September 2016 }}</ref> <ref name="seattlepi">{{cite web | url = http://www.seattlepi.com/archives/1999/9902100013.asp | title = Tech-savvy Getting Music For A Song; Industry Frustrated That Internet Makes Free Music Simple | first = Ruth | last = Schubert | access-date = 22 November 2008 | date = 10 February 1999 | work = Seattle Post-Intelligencer }}{{Dead link|date=August 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> <ref name="Giesler">{{ cite journal | doi = 10.1086/522098 | title = Conflict and Compromise: Drama in Marketplace Evolution | year = 2008 | last1 = Giesler | first1 = Markus | journal = Journal of Consumer Research | volume = 34 | issue = 6 | pages = 739–753 | citeseerx = 10.1.1.564.7146 | s2cid = 145796529 }}</ref> <ref name="mpeg1">{{cite web | publisher = International Organization for Standardization | year = 2006 | url = http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=25371 | title = ISO/IEC 11172-3:1993/Cor 1:1996 | access-date = 27 August 2009 | archive-date = 11 May 2011 | archive-url = https://web.archive.org/web/20110511043230/http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=25371 | url-status = live }}</ref> <ref name="Amorim">{{cite web | last = Amorim | first = Roberto | title = Results of {{nowrap|128 kbit/s}} Extension Public Listening Test | date = 3 August 2003 | url = http://listening-tests.freetzi.com/html/128kbps_Extension_public_listening_test_results.htm | access-date = 17 March 2007 | archive-date = 27 December 2011 | archive-url = https://web.archive.org/web/20111227161246/http://listening-tests.freetzi.com/html/128kbps_Extension_public_listening_test_results.htm | url-status = live }}</ref> <ref name="listening-test-128-2006">{{cite web | last = Mares | first = Sebastian | title = Results of the public multiformat listening test @ 128 kbps | date = December 2005 | url = http://listening-tests.freetzi.com/mf-128-1/results.htm | access-date = 17 March 2007 | archive-date = 21 November 2011 | archive-url = https://web.archive.org/web/20111121130652/http://listening-tests.freetzi.com/mf-128-1/results.htm | url-status = live }}</ref> <ref name="Dougherty">{{cite web | url = http://radar.oreilly.com/2009/03/the-sizzling-sound-of-music.html | title = The Sizzling Sound of Music | work = O'Reilly Radar | first = Dale | last = Dougherty | date = 1 March 2009 | access-date = 27 March 2009 | archive-date = 20 December 2009 | archive-url = https://web.archive.org/web/20091220055620/http://radar.oreilly.com/2009/03/the-sizzling-sound-of-music.html | url-status = live }}</ref> <ref name="noisey">{{cite web|url=https://www.vice.com/en/article/yntht-there-are-ghosts-in-your-mp3s/|title=Meet the Musical Clairvoyant Who Finds Ghosts In Your MP3s|work=NOISEY|date=2015-03-18|access-date=25 April 2015|archive-date=29 April 2015|archive-url=https://web.archive.org/web/20150429151109/http://noisey.vice.com/blog/yntht-there-are-ghosts-in-your-mp3s|url-status=live}}</ref> <ref name="schroeder2015">{{cite web|url=http://kernelmag.dailydot.com/issue-sections/features-issue-sections/12144/ghost-in-mp3-compression-audio/|title=The ghosts in the mp3|work=The Kernel |date=2015-03-15|access-date=25 April 2015|archive-date=14 June 2017|archive-url=https://web.archive.org/web/20170614081313/http://kernelmag.dailydot.com/issue-sections/features-issue-sections/12144/ghost-in-mp3-compression-audio/}}</ref> <ref name="hull2015">{{cite web|url=https://news.virginia.edu/content/lost-and-found-uva-grad-student-discovers-ghosts-mp3|title=Lost and Found: U.Va. Grad Student Discovers Ghosts in the MP3|work=UVA Today|date=2015-02-23|access-date=25 April 2015|archive-date=13 June 2015|archive-url=https://web.archive.org/web/20150613002703/https://news.virginia.edu/content/lost-and-found-uva-grad-student-discovers-ghosts-mp3|url-status=live}}</ref> <ref name="Maguire2014">{{Cite web |url=http://speech.di.uoa.gr/ICMC-SMC-2014/images/VOL_1/0243.pdf |title=The Ghost in the MP3 |access-date=25 April 2015 |archive-date=12 June 2015 |archive-url=https://web.archive.org/web/20150612184005/http://speech.di.uoa.gr/ICMC-SMC-2014/images/VOL_1/0243.pdf |url-status=live }}</ref> <ref name="Woon-Seng">{{cite book | title = Embedded signal processing with the Micro Signal Architecture | url = https://books.google.com/books?id=Lg0aN3vYw20C&q=128+kbit+mp3&pg=PA382 | author = Woon-Seng Gan | author2 = Sen-Maw Kuo | page = 382 | isbn = 978-0-471-73841-1 | year = 2007 | publisher = Wiley-IEEE Press | access-date = 16 November 2020 | archive-date = 10 March 2021 | archive-url = https://web.archive.org/web/20210310182738/https://books.google.com/books?id=Lg0aN3vYw20C&q=128+kbit+mp3&pg=PA382 | url-status = live }}</ref> <ref name="Bouvigne">{{cite web | last = Bouvigne | first = Gabriel | title = freeformat at {{nowrap|640 kbit/s}} and foobar2000, possibilities? | date = 28 November 2006 | url = https://hydrogenaud.io/index.php?PHPSESSID=aimg728m4eib19iggvujst7ju3&topic=38808.msg452751#msg452751 | access-date = 15 September 2016 | archive-date = 19 September 2016 | archive-url = https://web.archive.org/web/20160919091413/https://hydrogenaud.io/index.php?PHPSESSID=aimg728m4eib19iggvujst7ju3&topic=38808.msg452751#msg452751 | url-status = live }}</ref> <ref name="LAME_GPSYCHO">{{cite web | url = https://lame.sourceforge.net/vbr.php | work = LAME MP3 Encoder | title = GPSYCHO – Variable Bit Rate | access-date = 11 July 2009 | archive-date = 22 April 2009 | archive-url = https://web.archive.org/web/20090422172037/http://lame.sourceforge.net/vbr.php | url-status = live }}</ref> <ref name="TwoLAME">{{cite web | url = http://www.twolame.org/doc/vbr.html | title = TwoLAME: MPEG Audio Layer II VBR | access-date = 11 July 2009 | archive-date = 3 July 2010 | archive-url = https://web.archive.org/web/20100703052530/http://www.twolame.org/doc/vbr.html | url-status = live }}</ref> <ref name="MPEG-1 and MPEG-2 BC">{{cite web | author = ISO MPEG Audio Subgroup | url = http://mpeg.chiariglione.org/faq/mp1-aud/mp1-aud.htm#15 | title = MPEG Audio FAQ Version 9: MPEG-1 and MPEG-2 BC | access-date = 11 July 2009 | archive-date = 18 February 2010 | archive-url = https://web.archive.org/web/20100218081343/http://mpeg.chiariglione.org/faq/mp1-aud/mp1-aud.htm#15 | url-status = live }}</ref> <ref name="brandenburg">{{ cite web | url = http://www.telos-systems.com/support/tech-talk/138-guest-papers/267-mp3-and-aac-explained | title = MP3 and AAC Explained | last = Brandenburg | first = Karlheinz | year = 1999 | format = PDF | archive-url = https://web.archive.org/web/20141019025919/http://www.telos-systems.com/support/tech-talk/138-guest-papers/267-mp3-and-aac-explained | archive-date = 19 October 2014 }}</ref> <ref name="Limitations">{{ cite web | url = http://www.mp3-tech.org/content/?Mp3%20Limitations | title = MP3 Tech — Limitations | last = Bouvigne | first = Gabriel | year = 2003 | archive-url = https://web.archive.org/web/20110107101602/http://www.mp3-tech.org/content/?Mp3%20Limitations | archive-date = 7 January 2011 }}</ref> <ref name="LAME Y">{{cite web | title = LAME Y switch | url = http://wiki.hydrogenaud.io/index.php?title=LAME_Y_switch | website = Hydrogenaudio Knowledgebase | access-date = 23 March 2015 | archive-date = 2 April 2015 | archive-url = https://web.archive.org/web/20150402132607/http://wiki.hydrogenaud.io/index.php?title=LAME_Y_switch | url-status = live }}</ref> <ref name="Rae">{{cite web | last1 = Rae | first1 = Casey | title = Metadata and You | url = https://futureofmusic.org/blog/2009/08/06/metadata-and-you | website = Future of Music Coalition | access-date = 12 December 2014 | archive-date = 29 June 2017 | archive-url = https://web.archive.org/web/20170629225326/https://futureofmusic.org/blog/2009/08/06/metadata-and-you }}</ref> <ref name="Patel">{{cite conference|title=Performance of a Software MPEG Video Decoder|first1=Ketan|last1=Patel|first2=Brian C.|last2=Smith|first3=Lawrence A.|last3=Rowe|conference=ACM Multimedia 1993 Conference|url=http://www.cs.unc.edu/~kmp/publications/mm93/MM93-paper.pdf|access-date=1 July 2019|archive-date=2 September 2019|archive-url=https://web.archive.org/web/20190902110246/http://www.cs.unc.edu/~kmp/publications/mm93/MM93-paper.pdf|url-status=live}}</ref> <ref name="mpegfa31.txt">{{cite web | url=http://bmrc.berkeley.edu/research/mpeg/software/Old/mpegfa31.txt | title=The MPEG-FAQ, Version 3.1 | date=14 May 1994 | archive-url=https://web.archive.org/web/20090723213246/http://bmrc.berkeley.edu/research/mpeg/software/Old/mpegfa31.txt | archive-date=23 July 2009 }}</ref> <ref name="big-list">{{cite web | title = A Big List of MP3 Patents (and supposed expiration dates) | url = http://www.tunequest.org/a-big-list-of-mp3-patents/20070226/ | work = tunequest | date = 26 February 2007 | access-date = 19 March 2007 | archive-date = 2 March 2007 | archive-url = https://web.archive.org/web/20070302043255/http://www.tunequest.org/a-big-list-of-mp3-patents/20070226/ | url-status = live }}</ref> <ref name="Cogliati">{{cite web | url = http://www.kuro5hin.org/story/2008/7/18/232618/312 | title = Patent Status of MPEG-1, H.261 and MPEG-2 | work = Kuro5hin | first = Josh | last = Cogliati | date = 20 July 2008 | access-date = 6 October 2009 | archive-date = 16 September 2008 | archive-url = https://web.archive.org/web/20080916215441/http://www.kuro5hin.org/story/2008/7/18/232618/312 | url-status = live }} This work failed to consider patent divisions and continuations.</ref> <ref name="US5812672">{{USPTO Patent|patnum=5812672}}</ref> <ref name="Patent expiration">{{cite web|url=http://www.osnews.com/story/24954/US_Patent_Expiration_for_MP3_MPEG-2_H_264|title=US Patent Expiration for MP3, MPEG-2, H.264|publisher=OSNews.com|access-date=22 July 2011|archive-date=2 April 2013|archive-url=https://web.archive.org/web/20130402184109/http://www.osnews.com/story/24954/US_Patent_Expiration_for_MP3_MPEG-2_H_264|url-status=live}}</ref> <ref name="ffii">{{ cite web | title = Acoustic Data Compression – MP3 Base Patent | publisher = Foundation for a Free Information Infrastructure | date = 15 January 2005 | archive-url = https://web.archive.org/web/20070715144709/http://eupat.ffii.org/patents/samples/ep287578/index.en.html | archive-date = 15 July 2007 | url = http://eupat.ffii.org/patents/samples/ep287578/index.en.html | access-date = 24 July 2007 }}</ref> <ref name="Technicolor">{{cite web | url=http://www.technicolor.com/en/hi/discover/intellectualproperty | title=Intellectual Property & Licensing | publisher=Technicolor | archive-url=https://web.archive.org/web/20110504042035/http://www.technicolor.com/en/hi/discover/intellectualproperty | archive-date=4 May 2011 }}</ref> <ref name="Kistenfeger">{{ cite web|first=Muzinée |last=Kistenfeger |title=The Fraunhofer Society (Fraunhofer-Gesellschaft, FhG) |publisher=British Consulate-General Munich |date=July 2007 |url=http://www.britischebotschaft.de/en/embassy/r&t/notes/rt-fs005_Fraunhofer.html |archive-url=https://web.archive.org/web/20020818073018/http://www.britischebotschaft.de/en/embassy/r%26t/notes/rt-fs005_Fraunhofer.html |archive-date=18 August 2002 |access-date=24 July 2007 }}</ref> <ref name="chillingeffects">{{cite web | title = Early MP3 Patent Enforcement | publisher = Chilling Effects Clearinghouse | date = 1 September 1998 | url = http://www.chillingeffects.org/patent/notice.cgi?NoticeID=464 | access-date = 24 July 2007 | archive-date = 19 August 2014 | archive-url = https://web.archive.org/web/20140819225409/https://www.chillingeffects.org/patent/notice.cgi?NoticeID=464 | url-status = dead }}</ref> <ref name="ZDNet India">{{ cite web | title = Audio MPEG and Sisvel: Thomson sued for patent infringement in Europe and the United States — MP3 players stopped by customs | work = ZDNet India | date = 6 October 2005 | url = http://www.zdnetindia.com/news/pressreleases/stories/128960.html | archive-url = https://web.archive.org/web/20071011105618/http://zdnetindia.com/news/pressreleases/stories/128960.html | archive-date = 11 October 2007 | access-date = 24 July 2007 }}</ref> <ref name="SISVEL">{{ cite web | url = http://www.sisvel.com/index.php/sisvel-news/156-sisvel-grants-motorola-an-mp3-and-mpeg-2-audio-patent-license | title = grants Motorola an MP3 and MPEG 2 audio patent license | publisher = SISVEL | date = 21 December 2005 | access-date = 18 January 2014 | archive-url = https://web.archive.org/web/20140121041554/http://www.sisvel.com/index.php/sisvel-news/156-sisvel-grants-motorola-an-mp3-and-mpeg-2-audio-patent-license | archive-date = 21 January 2014 }}</ref> <ref name="SanDisk MP3 seizure">{{ cite web | first = Erica | last = Ogg | title = SanDisk MP3 seizure order overturned | work = CNET News | date = 7 September 2006 | url = http://news.cnet.com/2100-1047_3-6113326.html | access-date = 24 July 2007 | archive-url = https://web.archive.org/web/20121104164009/http://news.cnet.com/2100-1047_3-6113326.html | archive-date = 4 November 2012 }}</ref> <ref name="Patent Wild West">{{cite web | title = Sisvel brings Patent Wild West into Germany | work = IPEG blog | date = 7 September 2006 | url = http://ipgeek.blogspot.com/2006/09/sisvels-brings-patent-wild-west-into.html | access-date = 24 July 2007 | archive-date = 23 May 2007 | archive-url = https://web.archive.org/web/20070523032100/http://ipgeek.blogspot.com/2006/09/sisvels-brings-patent-wild-west-into.html | url-status = live }}</ref> <ref name="law360">{{ cite web | title = Apple, SanDisk Settle Texas MP3 Patent Spat | work = IP Law360 | date = 26 January 2009 | url = http://www.law360.com/registrations/user_registration?article_id=84475 | access-date = 16 August 2010 }}</ref> <ref name="Kelly">{{ cite web | title = Baker Botts LLP Professionals: Lisa Catherine Kelly — Representative Engagements | work = Baker Botts LLP | url = http://www.bakerbotts.com/lawyers/detail.aspx?id=2aa26940-06f4-44a3-865e-12b66912eed5 | access-date = 15 September 2016 |archive-url=https://web.archive.org/web/20141210220753/http://www.bakerbotts.com/lawyers/detail.aspx?id=2aa26940-06f4-44a3-865e-12b66912eed5 |archive-date=10 December 2014}}</ref> <ref name="MP3 payout">{{cite news | url = http://news.bbc.co.uk/2/hi/business/6388273.stm | access-date = 30 June 2008 | work = BBC News | date = 22 February 2007 | title = Microsoft faces $1.5bn MP3 payout | archive-date = 2 November 2008 | archive-url = https://web.archive.org/web/20081102042713/http://news.bbc.co.uk/2/hi/business/6388273.stm | url-status = live }}</ref> <ref name="Microsoft wins reversal">{{cite web | title = Microsoft wins reversal of MP3 patent decision | url = http://news.cnet.com/8301-10784_3-9755745-7.html | access-date = 17 August 2010 | website = CNET | date = 6 August 2007 | archive-date = 30 December 2013 | archive-url = https://web.archive.org/web/20131230071338/http://news.cnet.com/8301-10784_3-9755745-7.html | url-status = live }}</ref> <ref name="Alcatel-Lucent">{{ cite web|title=Court of Appeals for the Federal Circuit Decision |url=http://www.cafc.uscourts.gov/opinions/07-1546.pdf |date=25 September 2008 |archive-url=https://web.archive.org/web/20081029083229/http://www.cafc.uscourts.gov/opinions/07-1546.pdf |archive-date=29 October 2008 }}</ref>
</references>
==Further reading== * {{cite journal |url=https://computationalculture.net/article/reflections-on-the-mp3-format |journal=Computational Culture |date=9 November 2014 |author=Geert Lovink |title=Reflections on the MP3 Format: Interview with Jonathan Sterne |number=4 |issn=2047-2390 |author-link=Geert Lovink |access-date=14 August 2015 |archive-date=22 August 2015 |archive-url=https://web.archive.org/web/20150822035041/http://computationalculture.net/article/reflections-on-the-mp3-format |url-status=live}}
== External links == {{commons category|MP3}} {{Prone to spam|date=April 2013}} <!-- {{No more links}}
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--> * [https://www.mp3-history.com/ MP3-history.com] {{Webarchive|url=https://web.archive.org/web/20200211201051/https://www.mp3-history.com/ |date=11 February 2020 }}, The Story of MP3: How MP3 was invented, by Fraunhofer IIS.<!-- https://web.archive.org/web/20070610231859/http://www.iis.fraunhofer.de/EN/bf/amm/mp3history/mp3history03.jsp --> * [https://www.mp3newswire.net/sect/archive.htm MP3 News Archive]. {{Webarchive|url=https://web.archive.org/web/20190303201456/https://www.mp3newswire.net/sect/archive.htm |date=3 March 2019 }} – over 1000 articles from 1999 to 2011 focused on MP3 and digital audio. * [https://www.mpeg.chiariglione.org/ MPEG.chiariglione.org] {{Webarchive|url=https://web.archive.org/web/20240410005848/https://mpeg.chiariglione.org/ |date=10 April 2024 }} – MPEG official website
{{Compression formats}} {{MPEG}} {{Music technology}} {{Authority control}}
Category:MP3 Category:Computer-related introductions in 1993 Category:Audio codecs Category:Data compression Category:MPEG Category:Technicolor SA