download youtube chaptered videos into separate files, without downloading chapters that already exist based on checking on the names

youtube-downloader.py

import os, sys
from pathlib import Path
import yt_dlp

url = sys.argv[1] if len(sys.argv) > 1 else None
download_root = sys.argv[2] if (len(sys.argv) > 2) else None
proxy = sys.argv[3] if (len(sys.argv) > 3) else None
if (None in [url, download_root, proxy]):
    raise RuntimeError('Missing arguments.')

titles = set(Path(fn).stem for fn in os.listdir(download_root))

def get_sections_to_download(info, ydl):
    if (info.get('chapters')):
        chapters = []
        for chapter in info.get('chapters'):
            title = chapter['title']
            if (len([x for x in titles if title.startswith(x)]) == 0):
                titles.add(title)
                chapters.append(chapter)
        if (chapters):
            return chapters

    raise RuntimeError('No chapter needs downloading.')

def video_filter(info, *, incomplete: bool):
    if (not info.get('title')): return
    if (info.get('live_status') in {'is_live', 'was_live'}):
        return 'Skipping live stream'

opt = {
    'proxy': proxy,
    'format': 'bestvideo+bestaudio/best',
    'paths': { 'home': download_root },
    'outtmpl': {
        'default': '%(section_title,title)s.%(ext)s'
    },
    'download_ranges': get_sections_to_download,
    'match_filter': video_filter,
    'ignoreerrors': True
}

with yt_dlp.YoutubeDL(opt) as dl:
    dl.download(url)