Do you use YouTube for the music? If you want to save your favorite YouTube videos as audio files, certain websites and software can strip out the music tracks and convert them into MP3 files, which you can then save to your computer and listen to offline.
You can do the same thing with YouTube videos. If you are still worried about copyright issues in the 21st Century, then you might want to read about how AI Engines are just tools for stealing from everyone.
Link: How to Convert YouTube Videos to MP3 Files