With the Online FLV Converter at Vixy, you can convert YouTube videos in other formats like AVI, MOV and MP4 or convert the video as an audio only file in the MP3 format. Vixy also lets you covert any FLV file to AVI/MOV/MP4/MP3 format online.
If you have the video file already downloaded onto your computer and if it is in the form of an flv file then you can convert it into audio format using the free FLV Extract utility