Thanks for the share Ezil.
But there is also a technique on which you don't have to download any software anymore to get FLV Files.

It's one of Mozilla's Addons.

But the problem really is the FLV - Mp3 Converter.
Some FLV To MP3 Converters need to have registration fees and stuffs like that. Some Converters also can convert 1 minute of the file.

Some Converters also reduce the quality of the FLV. Coz sometimes the 4mb FLV becomes 1mb

The sound quality is obviously bad.
I'm still looking for a good one though.

Oh anyway, this is the converter I use
http://www.flv2mp3.com
It's just an online converter, but it produces a high quality mp3.