Film making

Either will be perfect for you as a beginner. D5100 has a revolving/flip screen you can pull out that makes it much much easier to shoot video - both in allowing you to hold the camera to keep it stable and getting in different angles/moving around and still being able to see what you are recording. I think that flip screen is invaluable for video, and though you can buy one for the D3200, it'll prob cost more than the camera :D You may want to look at what Canon has in the same price range, and if you are looking at filming primarily, consider a dedicated video camera: you can get one for a few hundred bucks and results are fantastic as they're designed for filming, these are designed for taking photos first, video a distant second... and you'll save a lot of money!

The person who said to buy the Canon 7D didn't mention that is is 3 times the price of the D5100 and nearly 3 times the price of the D3200. Either camera would be a great choice.