Perhaps this is correct. You need to know copyrights. But when there are such situations like haste or do not want to dig for a long time in the licenses, then the sites like flvconverter.net come where you can change the YouTube video to mp3 music for free and without registration. Even in the forums YouTube raised this question.
They responded that you need to watch the video then put a name, then do it your way.
I want to see your opinion
Anytune will extract the audio from common video file formats. When you import a video file the audio component will be added to Anytune’s music library.
For example if you took a video of your band practice and imported the file in Anytune you could loop, slow down, EQ, ….
I just use the new screen recorder on ios11 record the video thrn find in in my photos app and transfer it to dropbox then import it on anytune . Simple works great no apps to buy if you dont know how to set up screen recorder there are several youtube videos available