At midnight on March 20, 2017, Dolby's last relevant patent on Dolby Digital expired.
ETSI TS 102 366: Digital Audio Compression (AC-3, Enhanced AC-3) Standard
|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|
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.
AC-3 supports up to 5.1 surround sound.
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 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.
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:
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.
Hopefully never! In practice, there are a few cases:
No, of course not. AC-3 is over 25 years old and horribly inefficient.
There are multiple open source implementations of the AC-3 encoder and decoder. Some general guidance:
The following open source libraries implement AC-3:
--disable-everything --enable-decoder=ac3 --enable-demuxer=ac3 --enable-parser=ac3(then enable other parsers, demuxers, muxers, decoders, and encoders that you need)
--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)
--disable-everythingas your first
./configureoption. This will help protect your product from unnecessary intellectual property disputes as well as some security vulnerabilities. If you have not added
--disable-everythingas your first option, you should at least manually disable the encoders, decoders, muxers, demuxers, and parsers for
liba52 (GPLv2) used by VLC and others
valib from AC3Filter (GPLv2)
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:
ac3enc.cin 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.