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A Big List of MP3 Patents (and supposed expiration dates)

By tunequest February 26, 2007
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So, by now, large portions of the internet are abuzz with the Federal jury decision that Microsoft has been violating some of Alcatel-Lucent’s patents on the MP3 file format, which ahas been the backbone of the digital music revolutions and without which iTunes and the iPod would not have been possible.

I couldn’t help but note the timing of the ruling, since I had been been researching MP3 patents a couple weeks while working on a recent post. I came across the realization that the MP3 patents will soon start to expire, as early as this year in one case. So last week’s news got me wondering two things:

  • whether there is an aspect of "cashing-in-while-possible" going on with the current suits
  • just what the are all the MP3 patents, and when do they expire?

I can’t really speculate to that first point, but for the second, it’s fortunate that Thomson, the company that handles MP3 licensing has a neatly compiled list published at Of the twenty patents listed there, eighteen are filed in the U.S., to which this list is limited. These are the patents that everyone who makes an MP3-related product has licensed. We’ll get to those.

First though, here are the Alcatel-Lucent patents that Microsoft was found guilty of violating. This information was taken from the US Patent and Trademark Office. Since I’m no patent attorney, all expiration dates are best guesses based on quick summary research. Changes to U.S. patent law and the GATT treaty in the mid-90s (while mp3 was being developed) complicates matters. Additionally, I have not a clue as to how to handle continuations of abandoned applications, so some of these could be way off.

If anyone more knowledgeable wishes to correct any of my guesses, I will happily revise this page. These are much too technical, both in legalese and technology for me, but still I find them fascinating from a layman’s point of view.

Patents are listed chronologically by expiration date, with links to USPTO official pages and Google Patent Search documents.

Alcatel-Lucent Patents

Perceptual coding of audio signals
google patent search

A technique for the masking of quantizing noise in the coding of audio signals is adapted to include geometric interpolation between the thresholds for a tone masking noise and for noise masking a tone, in order to reduce use of bit-rate capability where it is not necessary for transparent or high quality. The technique is usable with the types of channel coding known as "noiseless" or Huffman coding and with variable radix packing. The stereophonic embodiment eliminates redundancies in the sum and difference signals, so that the stereo coding uses significantly less than twice the bit rate of the comparable monaural signal. The technique can be used both in transmission of signals and in recording for reproduction, particularly recording and reproduction of music. Compatibility with the ISDN transmission rates known as 1 B, 2 B and 3 B rates has been achieved.

US Patent #: 5,341,457
Application #: 08/109,867
Filed: October 16, 1992
Granted: August 23, 1994
Expires: October 16, 2012

Rate loop processor for perceptual encoder/decoder
google patent search

A method and apparatus for quantizing audio signals is disclosed which advantageously produces a quantized audio signal which can be encoded within an acceptable range. Advantageously, the quantizer uses a scale factor which is interpolated between a threshold based on the calculated threshold of hearing at a given frequency and the absolute threshold of hearing at the same frequency.

US Patent #: RE39,080 (reissue of 5,627,938)
Application #: 10/218,232
Filed: December 30, 1988
Granted: April 25, 2006 (original granted May 6, 1997)
Expires: May 6, 2014

Thomson Patents

Transmission system (expired)
google patent search

A system for transmitting and receiving digitalized audio signals, particularly via satellites, wherein data sequences are arranged in timely succession within frames, wherein before transmission, the digitalized audio signal is converted to a digital signal representing the momentary frequency spectrum and, during subsequent coding of the digital audio signal to be transmitted, portions of this transformed signal are given different weights on the basis of psychoacoustic laws with respect to the accuracy of their representation.

US Patent #: 4,821,260
Application #: 07/135,511
Filed: December 16, 1987
Granted: April 11, 1989
Expired: December 16, 2007

Method of transmitting an audio signal
google patent search

A method of digital transmission of an audio signal, in which in order to save transmission and/or memory capacity, the digital signal is converted, before transmission, into signals representing the short-term spectrum of time sections of the digital signal and portions of this signal are processed on the basis of psycho-acoustic laws, with portions of this signal lying below given thresholds left unconsidered, with at least one first threshold being defined below which only amplitude values outside of psycho-acoustically differentiable frequency ranges are left unconsidered.

US Patent #: 4,942,607
Application #: 07/152,026
Filed: February 3, 1988
Granted: July 17, 1990
Expired: February 3, 2008

Method for transmitting a signal
google patent search

Transmitting a signal wherein the signals is segmented by means of windows into successive overlapping blocks, the partial signals contained in the blocks are converted by transformation into a spectrum, with the spectra then being coded, transmitted, decoded after transmission and converted back into partial signals by retransformation. Finally, the blocks containing the partial signals are joined in an overlapping manner, with the overlapping regions of the blocks being weighted such that the resultant of the window functions in the respective overlapped regions equals one. To 2.2. In order to avoid interferences in adjacent blocks upon changes in the signal amplitude, the length of the window functions is selected as a function of signal amplitude changes. The method is suitable for the treatment of audio and video signals which are subjected to data reduction during transmission.

US Patent #: 5,214,742
Application #: 07/585,127
Filed: January 26, 1990
Granted: May 25, 1993
Expired: May 25, 2010

Process for transmitting and receiving a signal
google patent search

A signal is divided by windows into successive blocks that overlap at least by 50% and signal sections contained in the blocks are evaluated by analysis windows. The signal sections contained in the blocks are subjected to a transformation which permits sub-sampling with compensation of the aliasing components such as, for example, the "time domain aliasing cancellation" method. The spectra resulting from the transformation are subsequently coded, transmitted, decoded after transmission and changed back to signal sections by re-transformation. The blocks including the signal sections are evaluated by synthesis windows and are joined together in an overlapping fashion. The window functions of the synthesis windows are determined in dependence on the window functions of the corresponding analysis windows in the overlap region.

US Patent #: 5,227,990
Application #: 07/824,848
Filed: May 17, 1990
Granted: July 13, 1993
Expired: July 13, 2010

Method for the transmission of a signal
google patent search

The process disclosed enables the "time domain aliasing cancellation" method to be extended systematically to larger block overlapping. The boundary conditions which, when using various modified transforms, the analysis and synthesis windows must comply with, can thus be given. The transform series must also be included in the design of each analysis and synthesis window in order to optimize for a given application, because this changes the boundry conditions with which an analysis window function can be determined. Design for analysis and synthesis windows have shown that analysis and synthesis properties obtained by multiple block overlapping are significantly better than those obtained by convential double block overlapping. The systematic method of the invention offers numerous possibilites for optimizing windows in special applications.

US Patent #: 5,384,811
Application #: 07/853,751
Filed: October 08, 1990
Granted: January 24, 1995
Expires: January 24, 2012

Method for determining the type of coding to be selected for coding at least two signals
google patent search

In the case of coding a plurality of signals which are not independent of e another, a selection of the suitable type of coding is made as a function of a similarity measure. According to one aspect of the invention, the similarity measure is determined by firstly coding one of the signals according to the intensity-stereo method and then decoding it in order to create a signal affected by coding error, whereupon the latter signal and the associated non-coded signal are transformed into the frequency domain. In the frequency domain, a selection or evaluation of the actually audible spectral components, as well as of the signal affected by coding error and of the associated signal not affected by coding error, is undertaken using a listening threshold which is determined by a psycho-acoustic calculation. Intensity-stereo coding is undertaken in the case of a high similarity measure, whereas otherwise a separate coding of the channels is performed.

US Patent #: 5,736,943
Application #: 08/557,046
Filed: July 08, 1994
Granted: April 7, 1998
Expires: January 24, 2012

Process for the detecting of errors in the transmission of frequency-coded digital signals
google patent search

Disclosed is a process for the detection of errors, respectively perceptible disturbances, in the transmission of frequency-coded digital signals and, in particular, audio signals transmitted in blocks by a transmitter to a receiver. The present invention is distinguished by that from the frequency coefficients of earlier and, if need be, future blocks, a decision function is formed, on the basis of which the occurrence of an error is determined, and that the frequency coefficient containing an error is not longer utilized for the evaluation of subsequent blocks.

US Patent #: 5,455,833
Application #:08/039,478
Filed: October 25, 1990
Granted: October 3, 1995
Expires: October 3, 2012

Method of reducing crosstalk in processing of acoustic or optical signals
google patent search

A method for reducing frequency crosstalk in the transmission of digitized audio signals. Signals from partial bands in which spectral components of specific frequencies occur as signal components and signals from partial bands in which spectral components occur as crosstalk components in the stop range, undergo a weighted summation. Following transmission, the partial band signals undergo an inverse operation to weighted summation. The method operates independently of the selected encoding process, and is consequently universally usable.

US Patent #: 5,559,834
Application #: 08/211,769
Filed: October 06, 1992
Granted: September 24, 1996
Expires: September 24, 2013

Method for transmitting a signal
google patent search

In a method of transmitting a signal wherein the signal is partitioned into windows comprised of overlapping blocks with each block containing a partial signal. The partial signal in each block is converted into a digital signal and individually coded with a selected window function f(n). The overlapping areas of the window functions are weighted such that the resultant of the overlapping functions in each block equals one. The coded signals are transmitted. The received signals are reconverted into partial analog signals. The window functions are selected in accordance with frequency changes in the original signal.

US Patent #: 5,321,729
Application #: 08/094,355
Filed: April 26, 1993
Granted: June 14, 1994
Expires: June 14, 2014 April 26, 2013

Process for transmitting and/or storing digital signals of multiple channels
google patent search

A process for transmitting and/or storing digital signals of multiple chals. This process is suited, in particular, for transmitting the five channels of 3/2 stereophony as well as for transmitting two stereo channels and three additional commentary channels. In this manner, by way of illustration, television programs with multi-language audio signals can be transmitted. This process is distinguished in that by reduction of the to-be-transmitted data, only a bit rate of 384 kbit/s is required for transmission. The reduction of the data is achieved by the K input channels being imaged in segments onto the N.ltoreq.K virtual spectral data channels, by the spectral data channels being quantized, coded, and transmitted taking into consideration the principles of psychoacoustics, and by K output channels being reproduced from the transmitted bit stream with the aid of a transmitted list from the N.ltoreq.K spectral data channels.

US Patent #: 5,706,309
Application #: 08/428,235
Filed: November 02, 1993
Granted: January 6, 1998
Expires: January 6, 2015

Method of coding a plurality of audio signals
google patent search

In a method of coding a plurality of audio signals, the left and the right basic channel as well as the central channel are combined by joint stereo coding so as to obtain a jointly coded signal, which is decoded so as to provide simulated decoded signals. The simulated decoded signals and two surround channels are combined by matricization by means of a compatibility matrix so as to form compatible signals which are suitable for decoding by existing decoders. In order to avoid audible disturbances caused by excessive energy contents of the compatible signals, which would occur if joint stereo coding and decoding were carried out prior to carrying out the matricization, the compatible signals or the simulated decoded signals are dynamically weighted by means of a dynamic correction factor in such a way that the compatible signals are approximated with regard to their energy to the energy of signals which would be obtained if the two basic channels and the central channel as well as the surround channels were matricized directly.

US Patent #: 5,701,346
Application #: 08/704,730
Filed: February 02, 1995
Granted: December 23, 1997
Expires: February 02, 2015

Digital adaptive transformation coding method
google patent search

A digital adaptive transformation coding method for the transmission and/or torage of audio signals, specifically music signals, wherein N scanned values of the audio signal are transformed into M spectral coefficients, and the coefficients are split up into frequency groups, quantized and then coded. The quantized maximum value of each frequency group is used to define the coarse variation of the spectrum. The same number of bits is assigned to all values in a frequency group. The bits are assigned to the individual frequency groups as a function of the quantized maximum value present in the particular frequency group. A multi-signal processor system is disclosed which is specifically designed for implementation of this method.

US Patent #: 5,742,735
Application #: 08/295,484
Filed: October 6, 1988
Granted: April 21, 1998
Expires: April 21, 2015

Method for reducing data in the transmission and/or storage of digital signals of several dependent channels
google patent search

A method for reducing data during the transmission and/or storage of the digital signals of several dependent channels is described in which the dependence of the signals in the channels, e.g. in a left and a right stereo channel, can be used for an additional data reduction. Instead of known methods such as middle/side encoding or the intensity stereo process that lead to perceptible interference in the case of an unfavourable signal composition, the method according to the invention avoids such interference, in that a common encoding of the channels only takes place if there is an adequate spectral similarity of the signals in the two channels. An additional data reduction can be achieved in that in those frequency ranges where the spectral energy of a channel does not exceed a predeterminable fraction of the total spectral energy, the associated spectral values are set at zero.

US Patent #: 5,812,672
Application #: 08/211,547
Filed: October 13, 1992
Granted: September 22, 1998
Expires: September 22, 2015

Digital encoding process
google patent search

A digital encoding process for transmitting and/or storing acoustical sigs and, in particular, music signals, in which scanned values of the acoustical signal are transformed by means of a transformation or a filter bank into a sequence of second scanned values, which reproduce the spectral composition of the acoustical signal, and the sequence of second scanned values is quantized in accordance with the requirements with varying precision and is partially or entirely encoded by an optimum encoder, and in which a corresponding decoding and inverse transformation takes place during the reproduction. An encoder is utilized in a manner in which the occurrence probability of the quantized spectral coefficient is correlated to the length of the code in such a way that the more frequently the spectral coefficient occurs, the shorter the code word. A code word and, if needed, a supplementary code is allocated to several elements of the sequence or to a value range in order to reduce the size of the table of the encoder. A portion of the code words of variable length are arranged in a raster, and the remaining code words are distributed in the gaps still left so that the beginning of a code word can be more easily found without completely decoding or in the event of faulty transmission.

US Patent #: 5,579,430
Application #: 08/380,135 (continuation of 07/768,239; abandoned)
Filed: January 26, 1995
Granted: November 26, 1996
Expires: November 26, 2016

Process of low sampling rate digital encoding of audio signals
google patent search

In a method for coding an audio signal digitized at a low sampling rate to obtain time domain audio samples. A frequency domain representation of the time domain audio samples is produced. The frequency domain representation includes successive frequency lines. These frequency lines are grouped into a plurality of scale factor bands. The successive frequency lines in a scale factor band are coded with the same scale factor. A plurality of regions is formed by grouping the scale factor bands, wherein successive scale factor bands form a region within which all the scale factors are coded with the same number of bits, which is determined according to the largest scale factor of the region. The scale factors assigned to scale factor bands within the highest region that includes the higher frequency successive frequency lines are set to zero. The frequency lines in the highest region are coded using the zero-valued scale factors that correspond to a multiplication factor of 1. The scale factors for the highest region, however, are not coded. Thus, the bits that would be required for coding these zero-valued scale factors are saved and can be used for a finer quantization of the rest of the spectrum. Additionally, this coding method when applied to ISO/IEC 13818-3 as a low sampling rate modification thereof only requires minimal changes with respect to this Standard.

US Patent #: 6,185,539
Application #: 09/077,395
Filed: February 19, 1997
Granted: February 6, 2001
Expires: February 19, 2017

Method and apparatus for encoding digital signals employing bit allocation using combinations of different threshold models to achieve desired bit rates
google patent search

A method for encoding a digitized audio signal which includes the step of selecting one of two or more psycho acoustic model provided for generating masking thresholds used in a data reduction process. The selecting criterion is the available data rate for the encoded bit stream. Each one of the two or more psycho acoustic models is adapted to a specific data rate of the encoded bit stream. In a second embodiment, the method includes the step of combining two or more masking thresholds resulting from different psycho acoustic models, thereby leading to a more accurate calculation of a masking threshold for the data reduction process. Further, there are appropriate apparatuses for the encoding of digitized audio signals.

US Patent #: 6,009,399
Application #: 08/838,297
Filed: April 16, 1997
Granted: December 28, 1999
Expires: April 16, 2017

Digital coding process for transmission or storage of acoustical signals by transforming of scanning values into spectral coefficients
google patent search

A digital coding process for the transmission and/or storage of acoustical signals and, in particular, of musical signals, in which N scanning values of the acoustical signals are transformed into M spectral coefficients. The M spectral coefficients are quantized in the first step. Following encoding, the number of bits required for representation is checked utilizing an optimum encoder. If the number of bits is greater than the prescribed number of bits, quantization and encoding is repeated in further steps until the number of bits required for representation does not exceed the prescribed number of bits, whereby the required quantization level is transmitted or stored in addition to the data bits. Transmission and/or storage of acoustical signals and, in particular, of musical signals is accordingly possible without subjective diminishment of quality of the musical signals while reducing the data rates by factor 4 to 6.

US Patent #: 5,924,060
Application #: 08/821,007
Filed: August 29, 1997
Granted: July 13, 1999
Expires: August 29, 2017

Process for reducing data in the transmission and/or storage of digital signals from several interdependent channels
google patent search

A process for reducing data in the transmission and/or storage of digital signals of several interdependent channels is described. As the signals from the channels are not independent of one another, an additional data quantity reduction is possible during transmission. In known processes for the coding of signals from two stereo channels, in the case of an unfavorable signal composition interference can be caused by the coding process and cannot be concealed by the signal actually present in the channel and consequently reduce listening enjoyment. In the process according to the invention and with the aid of the spectral values of corresponding blocks of several channels, there is a balancing of the necessary data rate for a separate coding of the two channels and for a joint coding. There is a joint coding of the channels for as long as the data rate for the joint coding does not exceed by a predeterminable value the data rate for the separate coding of the particular channel. In this case the spectral values of the corresponding blocks are similar, so that a joint coding is preferred. In the case of highly dissimilar signals the balancing leads to a separate transmission of the signals. In order to ensure that there is no interference, temporarily no use is made of the joint coding of several channels.

US Patent #: 5,703,999
Application #: 08/751,456
Filed: November 18, 1996
Granted: December 30, 1997
Expires: December 30, 2017


Ta-Da! There you have it: the primary interesection of the legal and technical worlds that have made the music revolution possible during the past ten years. I hope you found this list at least a little bit as interesting as I did. I know it will still be another 10 years, but I for one can’t wait to see what will happen to the MP3 format when it enters the public domain.

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Join the Discussion

  1. Alberto Guzmán Says:

    I’m not gonna wait 10 years, i’ll better switch to Vorbis Ogg.
    A free and very good quality option (even is a loss format)


  2. Matthew Flaschen Says:

    I believe patent 5,321,729 expires April 26, 2013, not June 14, 2014. IANAL, but per and elsewhere, for patents filed before June 8, 1995 it’s either 20 years from date of priority (usually application date) or 17 years from grant. It’s never 20 years from grant, as you had it.


    tunequest Reply:

    You do seem to be right there. My bad. Thanks for the correction!


    Matthew Flaschen Reply:

    No problem, but I actually just noticed a few others. 5,736,943 has the expiration date from the one above. I think it should be April 7, 2015. And I believe 5,579,430 should be January 26, 2015. 5,703,999 should be November 18, 2016.

    I find this list very useful, and definitely hope you keep maintaining it.


    Brad Reply:

    Not long now on this one! Less than 20 days left.


  3. thatismehahaha Says:

    omg 2018 that’s 10 years :(


    Tim Reply:

    Its only 4 years away now. Oh how time flies.


    Raj Reply:

    its only 3 years left now :-)


    Dallas Reply:

    Technically doesn’t the last one expire on august 29th, 2017, since the last one on list this shows 20 years after the expire date, and actually expires some time in 2016, twenty years after the filing date? That is only two years away. :-)


    Dallas Reply:

    shows 20 years after the grant date…

  4. Joshua Cogliati Says:

    This site claims to have more MP3 patents:


  5. Joshua Cogliati Says:

    This conference paper “A Continuous Media Player, Lawrence A. Rowe and Brian C. Smith, Proc. 3rd Int. Workshop on Network and OS Support for Digital Audio and Video,San Diego CA (November 1992)” in seems to imply that they had a working MPEG-1 decoder (Click on my name for the link to the paper). Since MPEG-1 contains MPEG-1 layer 3 audio, if this decoder had that, then that would count as prior art, and invalidate any patents on MP3 decoding that were filed after November 1993 (one year after the player was created). This would put the expiration date for MP3 decoding sometime in 2014. Does anyone have any information on this player?


  6. Joshua Cogliati Says:

    The near complete draft standard was publicly available according to the link (click on my name). The draft standard was published as ISO/IEC JTC/SC29, “Coded Representation of Picture, Audio and Multimedia/Hypermedia Information”, Committee Draft of Standard ISO/IEC 11172, December 6, 1991.
    This means, I believe, that any MP3 patent filed after December 6, 1992 has prior art that can be used to invalid it. I think that puts decoding being patent free no later than December of 2012.


  7. Paul-Andre Gollier Says:

    unfortunately, this list is only related to US patent, just looking at the first (US5341457), it is part of a patent family of 19 patents in different countries! Fortunately USPTO was the only one to calculate the validity of patents from the granting date! so many of those patents will expire earlier in other countries. The European counterpart for this patent will for example expire next month ;) Furthermore, as belgian citizen, even if Belgium is part of Europe, this patent was not validated in my country ;)
    Long live to ogg and other open standards!

    Best regards from Belgium…


  8. Dacia Shelvin Says:

    I cannot thank you enough for the article post.Really thank you! Will read on…


  9. Yuhong Bao Says:

    “This means, I believe, that any MP3 patent filed after December 6, 1992 has prior art that can be used to invalid it. I think that puts decoding being patent free no later than December of 2012.”
    Unfortunately not, as the 17 year patent term is from the date of grant.


    Joshua Cogliati Reply:

    Yuhong Bao,
    The patent term is 20 years from the date of filing, or 17 years from the grant date for most of the patents that are listed. I took that fact into consideration when I made the comment.


    jmdesp Reply:

    So this means :
    - patent 5,703,999 5,924,060 6,009,399 6,185,539 5,579,430 5,701,346 5,706,309 5,321,729 were filed so late that they are doubts on their validity
    (However I checked 5,321,729 fully and it is a continuation of an application filed June 24, 1991, with foreign priority of a German patent filed Jun 29, 1990. So it’s likely valid. With the newer rules, it would already be expired :-( Three other patents were filed before summer 95 and may use a similar trick It would be great if Google/USPTO included *all* information from the cover sheet in their description, only the cover sheet says it’s a continuation/reference the foreign application here)
    - patent 5,812,672 and 5,559,834 : if we could find another publication a little earlier than the known one, they may also be invalidated (filed in october 1992, expire in 2015 and 2013). As october 1991 was a very late stage of the standard, it sounds like it was already available to some people. We don’t need a large availability for the invalidation, a single proven written disclosure without a NDA can be enough.
    - patent 5,455,833 and 5,341,457 : Will expire in October this year, only a few months to wait.

    At the end, after October this year almost everything relies on two submarine patents, that took almost 10 years to be granted after their filing :
    - 5,742,735 : Filed: October 6, 1988, Expires: April 21, 2015
    - 5,627,938 : Filed: December 30, 1988, Expires: May 6, 2014


    Josh Cogliati Reply:

    Sounds right. I wonder what claims exist in those patents, and if it would be possible to work around them.


  10. No No Says:

    5,924,060 has a USPTO filing date of March 20, 1997, not the August 29, 1997 stated in this article. (Its German original filing was August 29, but back in 1986!)

    Also, anybody doing research for themselves on this issue might want to look at another summary list at:


  11. No No Says:

    Also, 5,703,999 should be calculated as 20 years after file date, or November 18, 2016, not the December 30, 2017 stated in this article. Apparently notes December 30, 2014 as its expiration because of related earlier filings, but I have not verified this. A “blind” addition of 20 years from filing date is fine by me, because I’m looking for the last date MP3 royalties need be paid. For any future searchers, my reckoning is therefore: April 16, 2017.


  12. Samuel Says:

    There goes 5,321,729! Another one down.


  13. Epicanis Says:

    How many of these patents are actually essential for making ANY .mp3 file (as opposed to just some .mp3 files)?

    For example, I see some of those patents are for multiple-channel processing, so a mono (1-channel) .mp3 would not trespass on any of those patents.

    Have enough of the patents expired yet (as of today, 2014-09-26) to permit the production and use of limited “bare-bones” .mp3 files (e.g. single-channel, constant bitrate with no “advanced” processing) that would still be valid and play on “mp3 players”?

    Would be handy as a low-quality “fallback” format for hobbled Microsoft and Apple devices/browsers while everyone else can use .opus, ogg[vorbis], or .flac.


  14. darkhole Says:

    And we are getting closer!


    Joshua Cogliati Reply:

    Actually, I think MP3 is patent free in the United States.


  15. Joshua Cogliati Says:

    Here is my calculations for expiration:
    Patent Earliest file Expiration Date
    PATENT 5924060 1987/08/29 2007/08/29
    PATENT 4821260 1987/12/16 2007/12/16
    PATENT 4942607 1988/02/03 2008/02/03
    PATENT 5214742 1990/01/26 2010/05/25
    PATENT 5227990 1990/05/17 2010/07/13
    PATENT 5321729 1991/06/24 2011/06/24
    PATENT 5341457 1988/12/30 2011/08/23
    PATENT 5384811 1990/10/08 2012/01/24
    PATENT 5455833 1990/10/25 2012/10/03
    PATENT 5559834 1992/10/06 2013/09/24
    PATENT 5579430 1991/12/20 2013/11/26
    PATENT RE39080 1988/12/30 2014/05/06
    PATENT 5703999 1993/05/18 2014/12/30
    PATENT 5706309 1993/11/02 2015/01/06
    PATENT 5701346 1995/02/02 2015/02/02
    PATENT 5736943 1994/07/08 2015/04/07
    PATENT 5742735 1989/04/20 2015/04/21
    PATENT 5812672 1992/10/13 2015/09/22
    PATENT 6185539 1997/02/19 2017/02/19
    PATENT 6009399 1997/04/16 2017/04/16

    Basically all but two of them are expired.

    The last two filed were filed in 1997, but the MPEG-1 specification came out in August 1993, so these are well past that as prior art.

    Secondly, looking at the claims, (and I am not a lawyer) 6,185,539 seems to be discussion MPEG-2, and 6,009,399 seems to be discussing an encoding optimization compared to standard MPEG-1.

    So as I understand it, MP3 is now patent free in the United States.


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