how to use ffmpeg

how to convert mpg to flv:

use this command:
ffmpeg -i input.mpg -ar 44100 output.flv

another command:
ffmpeg -i input.mpg -deinterlace -ar 44100 -r 25 -qmin 3 -qmax 6 output.flv

how to extract audio from mpg:
ffmpeg -i "/path/to/file.mpg" -f flac "/path/to/newfile.flac"