The Nikon D4 is a professional large body DSLR. It weighs 3 pounds w/o lens. Unless you make your living as a photographer or a videographer, it will be really hard to justify the expense.
They are plenty of really, really good semi-pro DSLR (for video and stills) out there for half the cost and weighs about half as much; Nikon D800/800E, Canon 5D Mark III. Even a few of the mid-range DSLR ($2000 for body) are able to shoot pretty darn impressive video when there is adequate light.