IPhone 5 app that downloads YouTube videos for music?

On my old android phone, you could get an app where you download YouTube videos and save then I'm your music to listen anywhere. I know there are some apps like that for iphone but I've looked? I just want to download YouTube videos and be able to listen to them in no Wi-Fi like normal music. All the mp3 downloader apps never have the right songs, just covers

MyMedia allows you to download audio from youtube videos and name it, it then saves in the app for offline listening.