How to convert mpg file to flv file using ffmpeg or mencoder?

Here are the steps those I once used :

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I converted the video using ffmpeg command line as below.
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ffmpeg -i lions.mpg lions-ffmpeg.flv
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PS: input file name : lions.mpg

The video was converted fine.

Then I converted the video using mencoder using the command mentioned below.

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mencoder lions.mpg -o lions-mencoder.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 -vf scale=450:400 -srate 22050
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Then I generated a thumbnail using ffmpeg command mentioned below.

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ffmpeg -i lions-ffmpeg.flv -ss 1 -t 00:00:01 -s 120x90 -r 1 -f mjpeg lions.jpg
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Then I added meta data to the video.

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flvtool2 -U -P lions-ffmpeg.flv
hasKeyframes: true
hasMetadata: true
duration: 9.976
cuePoints:
audiosamplerate: 44000
audiodatarate: 63.0167957356935
datasize: 482188
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Try :)