I'd say that most modern consumer grade camcorders auto white balance in near real time. The little JVC Everio i've got will switch from sun to tungsten balance when i pan from a window shot to an indoor view. Yeah, there's a slight delay, maybe a second or two but i assume that's so that it isn't updating on every little colored thing that comes into view. A little lag is a lot better than having it flicker through the spectrum frame by frame.