Copyright?

I really like all things Harry Potter, so that's what my two videos are. The first is a fan-made Harry Potter #7 Trailer (it's fan-made because nothing has been officially released yet). Ok, so I think I understand this copyright v. fair use thing, but I have one question: is any fan-made or unofficial trailer a copyright infringement? These trailers usually last 1-4 minutes long and use music from the previous HP movies (usually #1) or another source that they don't cite. Likewise, the images are a montage of the previous movies and some leaked footage. Is this copyright infringement if it is less than 3 minutes of visual? The audio usually lasts that long, so does that make it infringement? In this specific case, they do cite the music they use, but they use more than 30 seconds of it. Also, because they use images from all 6 movies, is it less than 10% and therefore not an infringement? In my opinion, they are not obeying copyright laws because it is an unofficial trailer that they post on the internet.

The second YouTube video I chose to use was from Potter Puppet Pals: The Mysterious Ticking Noise (TMTN). This obeys copyright laws because its owner and creator posted it. But, although the storylines are original, are the characters under copyright with Warner Brothers? I think this is good copyright because of the original storyline and the creator posted it.