convert_pitch_by_semitones.py

#!/usr/local/bin/python3
"""
Requires you to install ffmpeg with all options (or at least the rubberband module): 
https://gist.github.com/Piasy/b5dfd5c048eb69d1b91719988c0325d8#gistcomment-2571754

Example usage: 
$ ./convert_pitch_by_semitones.py /input.mp3 /output.mp3 -2
"""

import sys
import subprocess
from math import pow

[_, input_file, output_file, semitones] = sys.argv
actual_pitch_difference = pow(2, (int(semitones) / 12))
subprocess.run(["ffmpeg", "-i", input_file, "-af", "rubberband=pitch=%.2f:pitchq=quality" % (actual_pitch_difference,), "-vn", output_file])