I implemented multithreading; however, I ran into an error: you cannot
work with JavaFX components outside of the main JavaFX execution thread.
So I removed it and, on a whim, tried the program without an
multithreading and, for some reason, it worked. If you run it right now,
you will see a terrible animation of a circle, and you will be able to
select a new song or change the visualization. It does not re-size
automatically yet.