iMovie from Apple is probably the best for video. Video cant be zoomed, and if it could, you shouldn't do it, As with still pictures the "zoom" is a digital zoom, which means, if you zoomed in 2x on the iPhone4 with a 5 megapixel resolution, you would have a 2.5 megapixel picture, likewise if you did a 4x zoom you would have a 1.25 megapixel picture. And that would look pretty bad even on a 4x5 enlargement.
My thinking is to take the best picture you can ,at full resolution, and then if you want to crop or zoom the picture, do it on a PC or Mac. There you have the computer power to enlarge it and even increase the resolution a little and still have the picture look good. Camera phones just can't do your precious pictures justice, when zoomed. Your computer can do a much better job.