You can use the free downloading software

It is easy to use:1. Run the software2. Click "Capture" tab3. The program auto get URL and list in Capture list.4. Click "Download" icon to start downloading.5. Find the downloaded FLV by right clicking and choosing "Location" hi, I recommend you use Nidesoft video converter to do it. thsi converter can convert between almost all popular video and audio formats in high quality at fast speed, it is also easy to use. you may use it to get audio file from flv video.