To quote from an Electronic Frontier Foundation (EFF) page,
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.
This is the format used to deliver 5.1 surround sound on many North American free-to-air TV channels. What this means is that satellite receiver manufacturers have one less patent to worry about.
This ought to put an end to some of the whining that occasionally appears in the satellite TV forums about cheap imported receivers that (in the opinion of the authors of the messages) violate patent laws, because the manufacturers allegedly did not purchase legitimate Dolby Digital licenses, yet included an AC-3 decoder in their receivers. Usually it is satellite equipment dealers that overbought on more expensive digital satellite receivers, and are sitting on old stock they’d like to sell, that complain about such things because they hate the competition (some dealers that have their own forums even censor discussion about such receivers, which strikes me as incredibly petty and self-serving, but it’s their forums). They fume that (in their opinion) such receivers enter the country illegally, and are sold more inexpensively than they should be, because the (usually Asian) manufacturer never cared about such things as paying patent license fees for their Dolby Digital decorder. Well as of today (March 20, 2017), payment is no longer required, according to this EFF article.
Manufacturers probably should avoid using trademarks such as “Dolby Digital” on their equipment, packaging, description of their product, in on-screen menus, etc. and instead stick to the non-trademarked “AC-3” designation, in order to stay on the right side of trademark law. And, as the article explains, this patent expiration only applies to AC-3 format. It does not apply to EAC-3 (“Dolby Digital Plus”), MLP, or TrueHD, which are still covered by several patents.
I am not a lawyer, and am only reporting what the EFF has to say about this, so if this matters to you, please consult your own lawyer for legal advice. Again, the article is here: At midnight on March 20, 2017, Dolby’s last relevant patent on Dolby Digital expired.
By the way, for anyone that’s ever had an argument with a friend or family member about whether a channel is carrying 5.1 audio (especially when Kodi claims it’s 2 channel, yet your ears tell you otherwise), note this article states that “AC-3 supports up to 5.1 surround sound”, and then further down, it also mentions AAC, DTS, and Opus as examples of other multichannel formats. So if Kodi shows the audio source as AAC or AC3, yes, it still might actually contain some form of 5.1 audio.