For those wondering what “optical sound” is: it’s a “means of storing sound recordings on transparent film” (https://en.wikipedia.org/wiki/Optical_sound https:/

For those wondering what “optical sound” is: it’s a “means of storing sound recordings on transparent film” (https://en.wikipedia.org/wiki/Optical_sound https://en.wikipedia.org/wiki/Optical_sound), in this context likely as sound on film, “a class of sound film processes where the sound accompanying a picture is recorded on photographic film, usually, but not always, the same strip of film carrying the picture. Sound-on-film processes can either record an analog sound track or digital sound track, and may record the signal either optically or magnetically. Earlier technologies were sound-on-disc, meaning the film's soundtrack would be on a separate phonograph record.” (https://en.wikipedia.org/wiki/Sound-on-film https://en.wikipedia.org/wiki/Sound-on-film)