@CailinJohnson
The Fair Use law states that you can copy or use a limited amount of a work without the permission of the copyright holder. However copyright law states that there needs to be a legal agreement about who can duplicate content. However with copyright law there is a public domain so after so many years that work because open to public use.
What is fair use and what is copyright has come under scrutiny because so many consumers have become producers and believe works should be available for public use.
All of the videos seem like they would be legal under the fair use laws. Each video is taking a little bit or piece of a work and tweaking it to make it their own. Such as the Disney Taxi cab, the producer of this video used animation and clips of Disney cartoons but did not use the whole cartoon in his film. Also the musician girl talk is taking bits and pieces of songs and changing them and making them different enough that they are no longer the same song.
The video that seems like it would be the most controversial to me is the Star Wars Fan Film: The Essence of the Force. This video is taking not just a little bit of the Star Wars theme but the whole video up until the end is the basic storyline of Star Wars complete with light sabers and costumes. This video follows the original Star Wars so closely it could be sued under copyright laws.