The only correct way to concatenate media files using ffmpeg

ffconcat.py

#!/usr/bin/env python3

import sys
import pathlib


def get_video_files() -> list[str]:
    video_formats: set = {
        ".mp4", ".mkv", ".webm", ".flv", ".avi", ".mts", ".mpg", ".m2ts", ".ts",
        ".mov", ".wmv", ".m4v", ".3gp", ".mpeg"
    }

    cwd = pathlib.Path(".")

    return sorted([
        f.name
        for f in cwd.iterdir()
        if f.is_file() and f.suffix.lower() in video_formats
    ])


def build_ffmpeg_command(files: list[str],
                         output_file: str,
                         resize_height: None | int = None):
    n = len(files)
    if n == 0:
        print("No video files in current working directory")
        return ""

    vfilter = f"scale=-1:{resize_height}" if resize_height else "null"

    cmd = "ffmpeg"

    for file in files:
        cmd += f" -i {file}"

    cmd += ' -filter_complex "'

    for i in range(0, n):
        cmd += f"[{i}:v:0]{vfilter}[v{i}];"

    for i in range(0, n):
        cmd += f"[v{i}][{i}:a:0]"

    cmd += f'concat=n={n}:v=1:a=1[outv][outa]" -map "[outv]" -map "[outa]" {output_file}'
    return cmd


def usage():
    print(f"Usage: {sys.argv[0]} <RESULT_FILENAME> [RESIZE_HEIGHT]")
    print("Examples:")
    print(f"\t{sys.argv[0]} result.mp4")
    print(f"\t{sys.argv[0]} output.mkv 720")
    print(f"\t{sys.argv[0]} video.mov 576")


def main():
    files = get_video_files()

    if len(sys.argv) == 2:
        cmd = build_ffmpeg_command(files, sys.argv[1])
    elif len(sys.argv) == 3:
        cmd = build_ffmpeg_command(files, sys.argv[1], int(sys.argv[2]))
    else:
        usage()
        exit(1)

    print(cmd)


if __name__ == "__main__":
    main()