ffmpeg how do i know what audio rate to use?

Question

Say I have something like this

ffmpeg -i video.avi -ar 22050 -ab 32 -f flv -s 320x240 video.flv 


-ar  (Audio sampling rate in Hz)
-ab  (Audio bit rate in kbit/s)

regarding the -ar and the -ab how do I know what rate to use? I got this ffmpeg command from a site somewhere and I was wondering how the person knew what values to put for the rates? Do I need to understand audio in order to figure that out?

Solution

You have to use "ffmpeg -i video.avi" to know the sampling rate and the bitrate of the audio stream in the source video.avi.

The audio stream can be extracted with the same sampling rate and bitrate without lose quality.

You can decide to reduce one of them for size reasons, but don't increment one of them to increase quality because you never can't upgrade the original quality.