The have a terms of service, and ripping in this way is against it.
"It IS illegal to convert copyrighted music videos into downloads. That said, nobody has been sued for this (yet).
Again, it is completely legal to watch any video you want on YouTube. Streaming from a legitimate site is permitted under copyright law. And if it doesn’t involve creating a video mp3 or download, you’re in the clear.
But, it IS illegal to create a personal download conversion of a copyrighted work under US copyright law. That includes an mp3, mp4, or any other download file type from your videos convert process."
https://www.digitalmusicnews.com/2016/10/10/youtube-to-mp3-s...