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.