How to legally convert youtube videos to my iPhone Music?

I was wondering if there was an app I could download in order to convert youtube music videos from YouTube to my music library without leaving my phone lol thanks

Download real player its virus free and its perfect i love it or on your phone get the downloads app and use flvto to convert links

YTD (YouTube Downloader) is great. You can use it to save the music videos to your phone or just the music like you said. Just install it on your computer and you have the option of choosing which file format you want. Its pretty straight forward.
You can get it from cnet
http://download.cnet.com/...47340.html

or from their site
http://www.youtubedownloadersite.com/

Here is a video on how to use it

And yes the music or videos are in high quality. And yes its free, just ignore yearly subscription, I have the free version and it works just fine.