iPhone/iTouch video stabilisation crop.

I'm aware the current advertised recording resolution for the newer iPhones and iPod touch 5G is 1080p (1920x1080).
I'm also aware that for digital video stabilisation to be achieved, the video is cropped to allow for motion adjustments.

I want to know, exactly HOW much is the video cropped? E.g. percentages, or resolution comparisons.

Thanks.