the prototype of the lp was the soundtrack disc used by the vitaphone motion picture sound system, developed by western electric and introduced in 1926. for soundtrack purposes, the less-than-five minutes of playing time of each side of a conventional 12-inch 78 rpm disc was not acceptable. the sound had to play continuously for at least 11 minutes, long enough to accompany a full reel of 35 mm film projected at 24 frames per second. the disc diameter was increased to 16 inches (40 cm) and the speed was reduced to revolutions per minute. unlike their smaller lp descendants, they were made with the same large "standard groove" used by 78s.