Quite awhile ago I tried to put up a video with a copyrighted track and Youtube said no. That's fair. They gave me the option of using one of their music tracks at no charge, but if you accept their offer then "ads may appear with your video." It was easier to add public domain music.
Movie Memories uses music for the introduction and later for the questions, all taken from a library of about 20 public domain music pieces written and performed before 1923. It's mostly ragtime, which goes with the nostalgia theme of Movie Memories. Sounds safe, but I got a copyright warning when I uploaded "In My Merry Oldsmobile" claiming that some company owned "Pickles and Peppers" as performed by Max Morath. The song was written in 1906, so where is the violation? They allowed the video to stay as is pending further review, but I replaced with different music.
The other warning is on Star Reporter in Hollywood. The film is in the public domain, clearly, but the theme song may have been copyrighted separately and may indeed be owned today by EMI Publishing. It is legal to show and sell this public domain film in its entirety, music included, but I don't want to debate the point with EMI and I have not heard from them. Why should I? There is no money to make and they don't monitor millions of warnings some computer spits out.
Here is the Movie Memory of "The Giant Claw" with PD music acceptable to Youtube: