by Ronnie Painter
Requires neither premium nor root.
A relatively simple script that allows you to save any YouTube video as an MP3 file with a filename of your choice.
-Works as of 2017/3/24 for most YouTube videos (fails some of the time for more obscure videos).
-On many devices, Android prohibits apps like Automate from writing files such as MP3s to your SD card, so I've set up the flow to write to the Music folder on the phone itself. If your device is not one of these (or if it's rooted), feel free to change the location of the file in block 23.
-And if you find this useful, hey, maybe you could consider being a cool dude/dudette and giving the flow an honest rating. Much appreciated!
Directions for use: Simply launch the flow, and it will begin monitoring the YouTube app for the use of the share button. Find the video you want to download the mp3 of, click "Share," and select the "Automate flow" option. It will then prompt you to enter the filename, and once you do that, it will automatically download the file to your "Music" folder.
Rate and review within the app in the Community section.