format has led to DTS-70 being reserved for niche engagements of 70 mm revivals and restorations. Dolby Digital has not been adapted to the 70 mm format. DTS-ES DTS-ES (DTS Extended Surround), introduced in March 1999 theatrically and in June 2000 for home theaters; includes two variants, DTS-ES Discrete 6.1, and DTS-ES Matrix 5.1, depending on how the sound was originally mastered and stored. Both variants are implemented in ways which are compatible with DTS decoders which do not include support for DTS-ES. DTS-ES Matrix provides 5.1 discrete channels, with a matrixed center-surround audio channel. DTS processors that are compatible with the ES codec look for and recognize "flags" built into the audio coding and "unfold" the rear-center sound from data that would otherwise be sent to rear surround speakers. DTS decoders which do not understand ES process the sound as if it were standard 5.1 and the matrixed audio for the center surround channel is output equally from the two surround speakers (very much as a sound intended to be in the center of the sound field in a stereo recording is played equally by the left and right speakers). This is notated as DTS-ES 5.1. DTS-ES Discrete provides 6.1 discrete channels, with a discretely recorded (non-matrixed) center-surround channel; in home theater systems with a 7.1 configuration, the two rear-center speakers play in mono. To maintain compatibility with DTS decoders which do not support DTS-ES, the center-surround channel is also matrixed into the left and right surround channels, so that the rear center channel's sound is still present when played in 5.1 on a non-ES system; an ES decoder removes the matrixed audio from these two channels when playing back DTS-ES Discrete soundtracks. DTS-ES Discrete is sometimes notated as DTS-ES 6.1. Only a few DVD titles have been released with DTS-ES Discrete. In contrast, Dolby's competing EX codec, which also boasts a center rear channel, can only handle matrixed data and does not support a discrete sixth channel; it is most directly comparable to DTS-ES Matrix. Note: The center-rear/surround channel is encoded and decoded in exactly the same way as the center-front. The center-surround channel can be decoded using any surround sound processor by feeding the left and right surround signals to the processor inputs. The left-Center-Right surround is produced. This will work for a "center-surround" reproduction, whether the source material is explicitly encoded, as in DTS-ES, or hidden