Buy a YouTube Music subscription
https://www.vidusoft.com/ This is the site I always use to download mp3 or mp4 from YouTube. It can be used in most video and audio sites, and it also has a mobile version.
you don't need to double post just to promote your site.
downloading music from Youtube is very simple. I simply go to Google on the first link and download the audio file, however the quality that we get when downloading from this service leaves much to be desired.
yup using mp3 downloader,but there are songs that exclusive in some sites so you cannot find them at youtube.