This is a handy tools I used very often lately, all it does is split the FLV files into Video and Audio files (FLV Stream in AVI and Audio in MP3.)

Very handy when you want the audio data only, drag and drop and done done.

You can download it from here:
http://cowscorpion.com/MultimediaTools/FLVExtract.html

.NET runtime 2.0+ is needed.