ffmpeg how do i know what audio rate to use?

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开发者_如何学运维 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?

Probably 44100 for audio sampling rate and 128 for bit rate should be sufficient.

Check Wikipedia's sampling rate and audio bit rate articles for examples to see if those values are too high or too low for what you're trying to do.

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.

I'm using -ar 22050 and -ab 48 for Avi and Mpeg video files. It works normally.