Camera [Q] Adaptive video windowing: Is it possible?

Maybe this is a commonly known technique that I just don't know about but I've been wondering for years now why this isn't done (maybe it is done). Current smartphone camera are now 13 Megapixels and more (the S4 is 4128x3096). HD video is recorded at 1920x1080. Is it possible to have a movable window of size 1920x1080 within that full 4128x3096 pixels of the camera sensor? Imagine having a stationary phone but video panning to follow a moving object. I know this is similar to how digital zoom works but I haven't seen it used for pan and follow.
Can this be done at an API level or is this something a new hardware driver would be needed to accomplish? I have not learned Android programming as yet so this is more of a conceptualization problem right now.