Be sure that you are clear that you did not do the original work and that you are using these "re-works" only as a demonstration of your skills. You don't want to appear to potential employers that you are trying to claim ownership over the original work.
If the owner of the video has a problem with you using their work, they will probably just sentsend you a notice to stop using it. If you stop, you'll be fine. I doubt you will have any problems.