ffmpeg wrapper for cutting files

cut-media.py

#!/usr/bin/env python3

import argparse
import os
import random
from re import fullmatch
from shutil import copyfile
from string import ascii_letters
import subprocess
import sys

def get_length(f):
    cmd = ["ffprobe", "-v", "error", "-show_entries", "format=duration", "-of", "default=noprint_wrappers=1:nokey=1", f]
    pipe = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
    output, err = pipe.communicate()
    if err is not None:
        print("error with the ffprobe command:", err)
        exit(2)
    try:
        return float(output)
    except ValueError:
        print("error with the ffprobe command: ffprobe output could not be converted to a float.")
        exit(2)
    except Exception as e:
        print("error with the ffprobe command:", e)
        exit(2)

def calculate_ffmpeg_seconds(cut, file_length):
    cut = cut.replace("[", "").replace("]", "")
    start_second, _, end_second = cut.partition(":")

    start_second = int(start_second) % file_length if start_second != '' else 0
    end_second = int(end_second) % file_length if end_second != '' else file_length

    plus_seconds = end_second - start_second
    if plus_seconds < 0:
        print("Error: start time was greater than the end time")
        exit(3)
    return str(start_second), str(plus_seconds)

def tempName(f):
    extension = f.split('.')[-1]
    basename = ''.join(random.choice(ascii_letters) for i in range(10))
    return basename + "." + extension


if __name__ == "__main__":
    parser = argparse.ArgumentParser(description="cut an audio file using python slice syntax",
        epilog=f"example: {sys.argv[0]} [30:] speech.m4a speech-cut.m4a")
    parser.add_argument('-i', '--in-place', dest='in_place', action='store_true', help="overwrite the input")
    parser.set_defaults(in_place=False)
    parser.add_argument("slice", nargs=1, help="[start:end] (in seconds)")
    parser.add_argument("in_file", nargs=1, help="input file")
    parser.add_argument("out_file", nargs="?", help="output file", default="DEFAULT")
    args = parser.parse_args()

    cut_seconds = args.slice[0]
    in_file = args.in_file[0]
    out_file = tempName(in_file) if args.out_file == "DEFAULT" else args.out_file

    if not fullmatch('^(\[(-?[0-9])+\:(-?[0-9])*\])|(\[(-?[0-9])*\:(-?[0-9])+\])$', cut_seconds):
        print("error: invalid time/slice argument.")
        exit(1)

    file_length = get_length(in_file)
    start_second, plus_seconds = calculate_ffmpeg_seconds(cut_seconds, file_length)

    command = ["ffmpeg", "-i", in_file, "-acodec", "copy", "-vcodec", "copy",
            "-async", "1", "-ss", start_second, "-t", plus_seconds, out_file]
    p = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)    
    out, err = p.communicate()
    if err is not None:
        print("Error running ffmpeg:")
        print(err)
    
    if args.in_place:
        os.remove(in_file)
        os.rename(out_file, in_file)

ffmpeg and python3 must be installed. On my system ffprobe came with ffmpeg.

The idea is to cut files using python's syntax for slicing arrays.