Sox can speed up mp3s in linux. Use the stretch paramater.
sox infile outfile effect
stretch factor [window fade shift fading]
Time stretch file by a given factor. Change duration without affecting the pitch. factor of stretching: >1.0 lengthen, <1.0 shorten duration. window size is in ms. Default is 20ms. The fade option, can be “lin”. shift ratio, in [0.0 1.0]. Default depends on stretch factor. 1.0 to shorten, 0.8 to lengthen. The fading ratio, in [0.0 0.5]. The amount of a fade’s default depends on factor and shift.