[Lucien Nunes]

In the early days of sound film there was such a thing, the sepopt (Separate optical) track. It was recorded by a device known as a 'sound camera' usually on academy 35mm. The problem with it as a stand-alone audio recording format was the cost - silver halide photochemistry has never been cheap and the cost of processing a roll of cine film was only tolerable given the large revenue a roll could generate. Fidelity was inherently limited by light valve and photocell performance and variability in photoprocessing results.