YouTube has a downloader for PC and mac but I don't know about an app though. You put the url in the box and it downloads the song in any format. Hope this helps.....also, can you help me with my questions, please?
I want a music app that can download music from youtube quickly, make playlists, and also does not need wifi?
There's no such thing as that. You need to have a connection 'cause youtube is online. The only thing you can do is to use some online mp3 converting sites for youtube.
