A script to download thumbnails of YouTube videos.

yt-thumb.py

#!/usr/bin/env python
"""
yt-thumb: a script to download thumbnails of YouTube videos of quantized set
of qualities (lowest, low, mid, high, highest). This tool nor the method it
uses imposes any restrictions on downloading thumbnails.

Qualities and their co-respoding width, height dimensions:
* lowest   120x90
* low      320x180
* mid      480x360
* high     640x480
* highest  1280x720
"""

import re
from   urllib.request import urlopen
from   urllib.error   import URLError
from   argparse       import ArgumentParser, FileType, RawTextHelpFormatter
from   functools      import partial
from   sys            import stdout
from   shutil         import copyfileobj

def extract_id_from_url(url: str):
    # Stripped version of the RegEx:
    # https://github.com/ytdl-org/youtube-dl/blob/master/youtube_dl/extractor/youtube.py#L372-L427
    return re.compile(r"""(?x)^(
                         (?:https?://|//)
                         (?:(?:(?:(?:\w+\.)?[yY][oO][uU][tT][uU][bB][eE](?:-nocookie|kids)?\.com/|
                            (?:www\.)?deturl\.com/www\.youtube\.com/|
                            (?:www\.)?pwnyoutube\.com/|
                            (?:www\.)?hooktube\.com/|
                            (?:www\.)?yourepeat\.com/|
                            youtube\.googleapis\.com/)
                         (?:.*?\#/)?(?:(?:(?:v|embed|e)/(?!videoseries))|(?:(?:(?:watch|movie)(?:_popup)?(?:\.php)?/?)?(?:\?|\#!?)(?:.*?[&;])??v=)))
                         |(?:youtu\.be|vid\.plus|zwearz\.com/watch|)/|(?:www\.)?cleanvideosearch\.com/media/action/yt/watch\?videoId=))?
                     (?P<id>[0-9A-Za-z_-]{11})(?!.*?\blist=(?:([0-9A-Za-z_-]{34})|WL))(?(1).+)?$""").match(url).groupdict().get('id')

class YouTubeThumbnailGrabber(ArgumentParser):
    Q2T = { 'highest': 'maxresdefault',
            'high'   :     'sddefault',
            'med'    :     'hqdefault',
            'low'    :     'mqdefault',
            'lowest' :       'default', }

    def __init__(self):
        ArgumentParser.__init__(self,
            description= __doc__,
            formatter_class= RawTextHelpFormatter)
        
        self.add_argument('URL',
            help= "YouTube-like video URL to grab (eg. 'youtu.be').")

        self.add_argument('OUT',
            nargs=   '?',
            default= stdout.buffer,
            help=    "output path of the downloaded thumbnail.\n"
                     "Tip: place '%%s' to replace with video ID.")

        self.add_argument('-q',
            default= '/'.join(self.Q2T.keys()),
            dest=    'qualities',
            choices= self.Q2T.keys(),
            help=    "quality scale of the thumbnail.")

        self.args = self.parse_args()

    def main(self):
        video_id = extract_id_from_url(self.args.URL)

        for imgq in self.args.qualities.split('/'):
            try:
                img = urlopen(f'https://i1.ytimg.com/vi_webp/{video_id}/{self.Q2T[imgq]}.webp')
                copyfileobj(img, open(self.args.OUT % video_id, 'wb') \
                                 if isinstance(self.args.OUT, str) else self.args.OUT)

                break
            except URLError:
                print(f'ERROR: {imgq} quality for video not found!'); continue

if __name__ == "__main__":
    YouTubeThumbnailGrabber().main()