1. Convert .FLV files into MPEG
 
ffmpeg -i I_KRmU2dO2M.flv -ab 56 -ar 22050 -b 500 -s 320x240 video.mpg

2. Convert .FLV into XviD .AVI with MP3 Audio:
 
ffmpeg -i I_KRmU2dO2M.flv -ab 56 -ar 22050 -b 500 -s 320x240 -vcodec xvid -acodec mp3 video.avi