The last patent on AC-3 (Dolby Digital) expires at midnight

Datetime:2017-03-20 05:18:53         Topic: Coder          Share        Original >>
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At midnight on March 20, 2017, Dolby's last relevant patent on Dolby Digital will expire.

Standard-Essential Patents Declared by Dolby

ETSI TS 102 366: Digital Audio Compression (AC-3, Enhanced AC-3) Standard

Expiration Patent Title
n/a US6246345 (E-AC-3 only) Using gain-adaptive quantization and non-uniform symbol lengths for improved audio coding
2017-03-19 US5890106 Analysis-/synthesis-filtering system with efficient oddly-stacked singleband filter bank using time-domain aliasing cancellation
2015-06-07 US5633981 Method and apparatus for adjusting dynamic range and gain in an encoder/decoder for multidimensional sound fields
2014-05-20 US5632003 Computationally efficient adaptive bit allocation for coding method and apparatus
2014-04-22 US5623577 Computationally efficient adaptive bit allocation for encoding method and apparatus with allowance for decoder spectral distortions
2013-12-10 US5583962 Encoder/decoder for multidimensional sound fields
2013-12-03 US5581653 Low bit-rate high-resolution spectral envelope coding for audio encoder and decoder
2012-12-26 US5479562 Method and apparatus for encoding and decoding audio information
2012-10-13 US5291557 Adaptive rematrixing of matrixed audio signals
2012-02-28 US5394473 Adaptive-block-length, adaptive-transforn, and adaptive-window transform coder, decoder, and encoder/decoder for high-quality audio
2011-10-18 US5357594 Encoding and decoding using specially designed pairs of analysis and synthesis windows
2011-06-21 US5274740 Decoder for variable number of channel presentation of multidimensional sound fields
2011-03-22 US5297236 Low computational-complexity digital filter bank for encoder, decoder, and encoder/decoder
2010-10-15 US5235671 Dynamic bit allocation subband excited transform coding method and apparatus
2010-05-12 US5752225 Method and apparatus for split-band encoding and split-band decoding of audio information using adaptive bit allocation to adjacent subbands
2009-12-29 US5109417 Low bit rate transform coder, decoder, and encoder/decoder for high-quality audio
2008-08-29 US4914701 Method and apparatus for encoding speech
2005-12-06 US4790016 Adaptive method and apparatus for coding speech

Source: Dolby IPR for TS 102 366 ( ETSI )

What is Dolby Digital (AC-3)?

AC-3 is a compressed digital audio format like MP3. It made its public debut in 1992. AC-3 has become the most common format for audio in film and television.

  • For digital television, AC-3 is a mandatory part of the ATSC standard (North America), DVB standards (Europe), and others.
  • For home video, AC-3 is a mandatory part of the DVD and Blu-ray standards.
  • For Internet streaming, AC-3 is supported in HTTP Live Streaming on many devices.

AC-3 supports up to 5.1 surround sound.

Has Dolby acknowledged that their last AC-3 patents are expiring?

In Dolby's 2005 S-1 filing with the SEC , Dolby acknowledged that AC3 patents expire in 2017.

"Patents relating to our Dolby Digital technologies expire between 2008 and 2017."

Dolby has only two AC-3 patents with 2017 expiration dates: US6449368 (expiring on 2017-03-14) and US5890106 (expiring on 2017-03-19).

Dolby provides a list of standard-essential AC-3/E-AC-3 patents to ETSI as part of the DVB standardization process. The last active AC-3 patent in this list expires on 2017-03-19. Dolby has not amended this list since 2004.

How does a public standard stay "patented" for longer than 20 years?

Dolby engages in legally dubious strategies known as "evergreening" to abuse the patent system and extend their licensing monopoly for AC-3. Some of these tactics include:

  • refusing to provide lists of their standard-essential patents in most cases ( see ATSC patent statements )
  • filing new patents, claiming that they cover portions of existing standards
  • acquiring irrelevant patents from competitors, alleging that they are now important to the standard

Will Dolby pretend that they still have patent rights to AC-3?


In 2012, Dolby bought a vague submarine patent from Panasonic, US6339757 ("Bit allocation method for digital audio signals"). The patent describes an optimization for audio encoders . (… for MiniDisc, using the Sony ATRAC codec.) Dolby has started claiming that Dolby Digital and all of their own products are already implementing this patent.

The good news:

  • The patent only affects encoders, not decoders.
  • Common open source implementations of the AC-3 encoder, such as ac3enc.c in ffmpeg's libavcodec, do not infringe this (incredibly vague) patent. In particular, they do not adjust bit allocation after initial initialization , and do not optimize bit allocation by psychoacoustic criteria.
  • Dolby hasn't updated their ETSI IPR listing of standard-essential patents to include US6339757, indicating that they do not believe this patent is required to implement an AC-3 encoder or decoder. In Panasonic's 9 years of ownership, they also did not allege that this patent was essential to AC-3 implementation, despite claiming numerous other standard-essential patents in DVD and digital television standards.
  • The patent was granted in 2002. Almost all existing AC-3 implementations have past the 6 year statute of limitations on patent infringement.


I'm a user. Why should I care?

You have probably paid many AC-3 license fees over the years. AC-3 license fees are part of the cost of TVs, game consoles, and other AV equipment sold in the last 25 years.

You may have had problems playing certain video files on your computers and mobile devices. In 2012, Dolby started threatening the authors of various video player apps, forcing developers to remove their apps, remove support for AC-3, or increase prices.


When would I need to decode AC-3?

  • Playing most live TV content
  • Playing most recorded TV content
  • Playing many videos from DVD
  • Playing many videos from Blu-Ray
  • Playing videos recorded by some digital camcorders
  • Playing some online streaming content offered in 5.1 surround sound

When would I need to encode AC-3?

Hopefully never! In practice, there are a few cases:

  • Encoding surround sound audio for some legacy TVs and devices that only support AC-3 for surround. Modern devices can decode other multichannel formats such as AAC, DTS, and Opus.
  • Encoding surround sound audio to be sent to a legacy AV receiver using an optical cable (S/PDIF). Modern AV receivers can accept other formats over HDMI, including multichannel PCM.

Is AC-3 any good? Should I use it for new stuff?

No, of course not. AC-3 is over 25 years old and horribly inefficient.

How can I safely use AC-3 in my app?

There are multiple open source implementations of the AC-3 encoder and decoder. Some general guidance:

  • Remove any code that encodes, decodes, parses, muxes, or demuxes E-AC-3 ("Dolby Digital Plus"), MLP, or TrueHD. These are still covered by several patents.
  • Avoid using trademarks such as "Dolby Digital" in your user interface, support articles, app description, and marketing materials. Use the generic terms "AC-3" or "A/52" to refer to the audio technology.

The following open source libraries implement AC-3:

  • libavcodec in ffmpeg (LGPLv2.1+) and libav (LGPLv2.1+)

    • Decoder and encoder for AC-3
    • To compile only the AC-3 decoder: --disable-everything --enable-decoder=ac3 --enable-demuxer=ac3 --enable-parser=ac3 (then enable other parsers, demuxers, muxers, decoders, and encoders that you need)
    • To compile the AC-3 decoder and the AC-3 encoder: --disable-everything --enable-encoder=ac3 --enable-decoder=ac3 --enable-muxer=ac3 --enable-demuxer=ac3 --enable-parser=ac3 (then enable other parsers, demuxers, muxers, decoders, and encoders that you need)
    • Warning : When preparing to use libavcodec in any product, you should always start by disabling all encoders, decoders, parsers, muxers, demuxers, bitstream filters, protocols, filters, and hwaccels, then selectively enabling the ones that your product absolutely needs. To do this, use --disable-everything as your first ./configure option. This will help protect your product from unnecessary intellectual property disputes as well as some security vulnerabilities. If you have not added --disable-everything as your first option, you should at least manually disable the encoders, decoders, muxers, demuxers, and parsers for eac3 , mlp , and truehd .
  • liba52 (GPLv2) used by VLC and others

    • Decoder only for AC-3
  • valib from AC3Filter (GPLv2)

    • Decoder and encoder for AC-3. Note: Build process does not allow easy removal of patented E-AC-3 code.

How can I make sure this never happens again?


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