There a simple way to convert YouTube videos to audio tracks by Youtube to MP3 Converter :
http://www.listentoyoutube.com/
Youtube to MP3 Converter is the most convenient online application for converting YouTube flash video to MP3 audio. This service is fast, free, and requires no signup. All you need is a YouTube URL, and our software will transfer the video to our server, extract the MP3, and give you a link to download the audio file.
If you have downloaded some videos from youtube, you can just extract sound from a YouTube video with a video converter.
http://i-loveshare.com/extract-audio-from-youtube-video/
In this way, you can save the YouTube sound in MP3, WMA, FLAC, AAC, AC3 audio as your need.