We work with large volumes of subtitles here and that's basically what we are aiming to do. There's a couple commercial solutions that still do a poor job for a hefty price tag, if that's the only thing you need from them. Not profitable compared with human sync unless you have to sync more than a couple hundred hours of content.
The BBC developed an "Assisted Subtitling" system which on paper is pretty fancy - accepts scripts in most common formats, automatically determines optimum colours for each speaker, processes video to find shot changes, uses voice recognition to spot the dialogue at the right points, and turns out an almost-complete subtitle file that just needs a look over by a human to ensure it's sensible.
Better still, it's now open source - although sadly the voice recognition part of it relies on a closed source commercial product which (at first glance) might not even still be available.
