bulk transcode to MP3 using multiple cores (relies on `ffmpeg`)

convert_to_mp3.py

#!/usr/bin/env python3

"""
Transcodes list of audio files specified as command-line arguments into
standard MP3s. Example:

```bash
./convert_to_mp3.py *.m4a
```

Actual transcoding is done via a subprocess call to ffmpeg. If multiple
cores are available, transcoding is parallelized via a pool of workers, each
of which transcodes one file at a time.

Taken from the public domain. 

Credit for Python 2 version goes to Chris Hiszpanski (https://github.com/hiszpanski).
Credit for Python 3 version goes to Shaun Wilson (https://github.com/wilson0x4d).
"""

import multiprocessing
import os
import signal
import subprocess
import sys

def init_worker():
    signal.signal(signal.SIGINT, signal.SIG_IGN)

def worker(fileurl):
    # Print informational message
    print(f"{multiprocessing.current_process().name} : converting {fileurl}")

    # Derive output filename
    (root, ext) = os.path.splitext(fileurl)
    outfile = root + ".mp3"

    # If output file exists, break out
    if os.path.exists(outfile):
        return

    # Call out to ffmpeg
    subprocess.call(["ffmpeg", "-y", "-loglevel", "quiet", "-i", fileurl, outfile])

if __name__ == '__main__':
    # Create a pool of workers (equal to number returned by cpu_count())
    pool = multiprocessing.Pool(initializer=init_worker)

    # Map conversion of files to pool of workers. Skip the program name itself.
    try:
        pool.map(worker, sys.argv[1:])

    except KeyboardInterrupt:
        print("Caught KeyboardInterrupt, terminating")
        pool.terminate()
        pool.join()