Shooting video with d5100?

What is the best way to focus with d5100 while shooting video. I don't like the auto becouse it hunts too much and the noise that lens makes. I used manual which I like but it is hard to tell that the subject is in perfect focus. And what is the best f- number,iso to use while shooting video? Thanks in advance.

Well, if you don't like the noise from the lens, you only other choice is manual. Your F number is going to be determined on what kind of DOF you want. If you want your subject in foucs and everything in the background blurred, then a small F number would work. If you want everthing clear, a bigger F number. ISO would be determined by the type of lighting you have. If you are out in under the sun, ISO 100 to 200. Indoors, go to 400.

In most cases I use use manual focus. For indoor using a f2.8 lens, my typical settings is f2.8, 1/60, and ISO 1000.