ffmpeg - avi to flv & mpg to flv

ffmpeg -y  -i sample.avi -threads 2 -s 320x240 -r 30.00 -threads 1 -pix_fmt yuv420p  -g 300  -qmin 3  -b 512k -async 50  -ar 11025 -ac 1 -ab 16k outputfile.flv

ffmpeg -y  -i sample.avi -threads 2 -s 320x240 -r 29.97 -threads 1 -pix_fmt yuv420p  -g 300  -qmin 3  -b 512k -async 50  -ar 44100 -ac 2 -ab 128k outputfile.flv

• -y: Overwrite output files
• -i ‘inputfile.avi’: Input filename
• -threads 2: Thread count
• -s 320×240: Set frame size
• -r 30.00: Set frame rate (fps)
• -threads 1: Thread count (again)
• -pix_fmt yuv420p: Set pixel format
• -g 300: Set the group of pictures size
• -qmin 3: minimum video quantizer scale (VBR)
• -b 512k: Set the video bitrate in bits/s
• -async 50: Audio sync method. “Stretches/squeezes” the audio stream to match the timestamps, the parameter is the maximum samples per second by which the audio is changed.
• -acodec mp3: Force audio codec to codec
• -ar 11025: Set the audio sampling frequency
• -ac 1: Set the number of audio channels
• -ab 16k: Set the audio bitrate in bits/s
• outputfile.flv: Is the outputfile

from : http://www.victorcastelan.net/convert-avi-mpeg-files-to-flv-with-ffmpeg/