Convert mp4 file to flv ?

use following linux command :

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/usr/local/bin/mencoder "video.mp4" -o "video.flv" -of lavf -oac mp3lame -lameopts abr:br=56 -ovc lavc -lavcopts vcodec=flv:vbitrate=800:mbd=2:mv0:trell:v4mv:cbp:last_pred=3 -srate 22050 -ofps 24 -vf harddup
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Input file name :video.mp4
Output file name : video.flv

try :)