A discrete audio format for digital multi-channel which is the official audio standard for HDTV (and DVD). Dolby Digital sound is usually associated with "surround" 5.1 channel. Although this configuration is common channel, is just one of many possible variations - a sound track "Dolby Digital" can mean anything from 1 to 5.1 channels.

Dolby Digital is a practical and cost-effective method of delivering digital sound to cinemas without the need for separate CDs.  The six-channel digital soundtrack is printed directly onto 35 mm film in the form of data blocks in the areas between the perforations.  A high-quality four-channel analog Dolby SR soundtrack is also provided on the same film, enabling playback in all cinemas.  The digital signal is decoded by a Dolby Digital cinema processor into six channels of sound which are then routed through six power amplifiers and into the speakers situated around the cinema.

Dolby Digital SR-D cinema soundtracks are optically recorded on a 35 mm release print using sequential data blocks placed between every perforation hole on the sound track side of the film. A CCD scanner in the projector picks up a scanned video image of this area, and a processor correlates the image area and extracts the digital data as an AC-3 bitstream. These data are finally decoded into a 5.1 channel audio source.

Dolby Digital audio is also used on DVD-Video and other purely digital media, like home cinema. In this format, the AC-3 bitstream is interleaved with the video and control bitstreams.