Actually, this turns out to be very easy (even though the process is not immediately clear). Even though syncing happens in iTunes, there’s no preference for video syncing in the iPhone management screen. Turns out you don’t need one.
People who use their iPhone cameras a lot generally sync their photos to a photo management programs (there are dozens of options, but Mac users likely use iPhoto a lot). This is where the video shot on your iPhone 3GS will end up.
To sync that video to your computer, simply connect your iPhone 3GS to your computer and open your photo management program. Import photos in your normal way. Coming along with the still photos will b your video.
Now that the video is on your computer, you can drag it, export it, or otherwise save it elsewhere for use in a video-editing program.
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