YMusic is a tool you can use to play YouTube video in background, and download video with variety formats (include MP3) totally FREE.

Why do you have to load full video data while you only want to enjoy the music (audio)? YMusic helps you save a lot of bandwidth because it only load audio of the video, now you can enjoy millions music video in YouTube without worrying about data wasted.
Main features:
- Play YouTube video in background
- Download YouTube with variety formats: mp3, opus, webm, mp4,...
- Search music video easily
- Browse trending music videos
- Customizable interface with 81 color combinations to choose from
- Auto download album art, Last.fm integration for retrieving artist images and descriptions
- Smart Playlists with fully customizable rules
- Custom equalizers
- Gapless playback
- Home screen widgets