Damn Sigma Lenses
Turns out at least one of my Sigma lenses won’t autofocus in my new D3200’s LiveView / movie mode.
I may have to go have them re-chipped by Sigma.
EDIT: Looks like AF for movies is pretty bad anyway. It over-focuses with major changes and then adjust with smaller changes, just like in picture mode. This is great for quick focusing, but really terrible for video where you want smooth focus adjustment. I’ll stick with manual focusing.