This is a little howto (in fact it’s only a note for me ) concerning conversion from one type into another using ffmpeg in the shell. You should have already installed ffmpeg

ffmpeg -i original.mpg -f flv -b 400000 -ac 1 -r 23 -s 320x240 video.flv

• i: input file
• f: output format
• b: bit rate (video)
• ac: number of audio channels
• r: frame rate
• s: size (widthxheight)

Update: There’s a video tutorial about ffmpeg here