This article is from the rec.arts.movies.tech FAQ, by Scott E. Norwood snorwood@nyx.nyx.net with numerous contributions by others.
The video timecode on the edited tape is converted to 24/25 fps film
timecode. This is then used to drive a standard magnetic film dubber,
which then records the sound from the tape directly onto magnetic
film. This is then used to make an optical soundtrack for film release
in the conventional fashion.
 
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