iMovie on iPhone 4 : How to divide audio
iMovie for iPhone 4 does not supply the capacity to divide the sound from the video clip of a flick. It just permits one track of audio - either a history track or the sound from the clip you're making use of. If you click and also hang on a clip it raises the Clip Settings watch where you can switch off the sound for the clip.
iMovie for iPhone 4 does not permit you to do anything programatically. If you're intending to create something with the iphone SDK to draw the sound from a flick I recommend editing and enhancing your inquiry and also checking out what you can do with AVFoundation