there are lot of of tools availabe
i.e.
http://www.flv2mp3.com/
[Free Flv to Mp3 Converter - convert Flv to MP3, extract audio from flv file and save to mp3.](http://www.smallvideosoft.com/flv-to-mp3/)
[Flv to mp3 Free Download](http://www.brothersoft.com/downloads/flv-to-mp3.html)