Convert mp3 to m4a with AAC codec and 128kb/s bitrate.

convert_mp3_to_m4a.rb

#!/usr/bin/env ruby

if ARGV.length < 1
    puts "Please input file name."
    exit
end

mp3_name = ARGV[0] + ""
m4a_name = mp3_name.split(".")[0] + ".m4a"
puts "******************************************"
puts "Converting #{mp3_name} to #{m4a_name} ..."
puts "******************************************"
command = "ffmpeg -i #{mp3_name} -c:a aac -b:a 128k #{m4a_name}"
exec command

How to use?

copy this file to destination and then

$ chmod +x ./convert_mp3_to_m4a.rb

make sure that you have installed ffmpeg(which could be installed through homebrew).

then, just type the script name and the name of mp3 file like

$ ./convert_mp3_to_m4a.rb music.mp3

it will automatically convert music.mp3 to music.m4a with AAC codec and 128kb/s bitrate.