Youtube video searcher and Audio Extractor for AudioSource.

I am developing a video game that needs a youtube Audio extractor to use in an AudioSource as a clip. The perfect example is the game "Music Racer" on Android where there is a search engine and you can select the video you want, that's exactly what I'm looking for. But I can't think of anything on how to make that finder nor use the audio from a youtube video in the AudioSource, if anyone knows how it's done or if you help me it would help me a lot.