First of all you probably don't want to try to record sound with a film camera unless you are a retro technology buff; nobody uses optical or magnetic camera sound anymore. That went away with the coming of video. Most modern film productions uses double system sound, where audio is recorded to a separate audio recorder such as a DAT, Nagra, or computer. If you've seen any "making of" videos, you recall the man with the slate saying "scene 1, take 1" and clapping the slate, providing a simple and reliably way for film editors to synchronize audio to image in the editing room. It worked in 1929, and it still works today.