ffmpeg

ffmpeg: Convert avi to flv (YouTube)

ffmpeg -i video.avi -ar 22050 -ab 32 -f flv -s 320×240 video.flv

-i input file name
-ar audio sampling rate in Hz
-ab audio bit rate in kbit/s
-f output format
-s output dimension

Syntax borrowed from: http://luar.com.hk/blog/?p=670