...by "realistic video" I suppose you mean 3D Computer Graphics, right? This requires HIRING a professional 3D Animator/Modeler and a CG Texture Artist. It isn't cheap, trust me. However, this could be accomplished bytrolling forums that 3D Artists areKNOWN to frequent and then making a prospective employee an offer. Newgrounds isn't exactly the best place to look.
IF you meant a video with actual "real" people in it, you'll need to buy or rent video and audio recording equipment and HIRE actors.
Either way, it costs money. Not many people, aside from close friends, will be willing to preform any type of labor for free. These are the breaks.