Recording video with option of manipulating the pixels before writing to file

Question

I know that I can access raw video images from the iPhone's camera with AVCaptureVideoDataOutput. I also know that I can record video to a file with AVCaptureMovieFileOutput. But how can I first access the raw video images, manipulate them and then write the manipulated ones into the video file? I've already seen apps in the app store, which do this, so it must be possible.

Answer 1

Ok, I now know, that it's done with AVAssetWriter.