Dolby Digital (AC-3)
Dolby's lossy codec for 5.1 surround, which went from the cinema to every DVD player and AV receiver.
AC-3 premiered in cinemas with Batman Returns in 1992, its data printed as digital blocks between the sprocket holes of the film. The codec is MDCT-based and packs six channels — five full-range plus a low-frequency effects channel, hence "5.1" — into a few hundred kbit/s.
LaserDisc picked it up in 1995, then it became standard on DVD and in American digital TV. The DVD player's digital output passed the AC-3 stream untouched to the receiver, which turned S/PDIF into a home-cinema accessory. Successors such as Dolby Digital Plus and Atmos have taken over streaming, but the old codec is still there as the fallback track almost everywhere.