I compress mp3 all the time
Use this... Install
ffmpeg.. Then type this in the directory where your files are located.
Code:
ffmpeg -i <input file nama> -ab xxx <out file name>
Here, replace <xyz> with the corresponding values with extension and xxx with the bitrate, ie 64,96,128 and the like..
Note : Your input file maybe in any recognisable audio/video format, and it'll still work.. i.e, .wav, .flv, .ogg , .wma etc......