Youtube-dl

http://rg3.github.com/youtube-dl/

Upgrade your installation!

Due to frequent changes to youtube (and other platforms youtube-dl supports), the software change frequently. Use pip to upgrade your installation to the latest version.

 sudo pip3 install --upgrade youtube-dl

Otherwise you'll see errors like the following.

[youtube] vP4iY1TtS3s: Downloading webpage
[youtube] vP4iY1TtS3s: Downloading video info webpage
ERROR: Signature extraction failed: Traceback (most recent call last):
  File "/usr/local/lib/python3.7/dist-packages/youtube_dl/extractor/youtube.py", line 1385, in _decrypt_signature
    video_id, player_url, s
  File "/usr/local/lib/python3.7/dist-packages/youtube_dl/extractor/youtube.py", line 1262, in _extract_signature_function
    raise ExtractorError('Cannot identify player %r' % player_url)
youtube_dl.utils.ExtractorError: Cannot identify player 'https://www.youtube.com/s/player/e3cd195e/player_ias.vflset/en_US/base.js'; please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; see  https://yt-dl.org/update  on how to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.
 (caused by ExtractorError("Cannot identify player 'https://www.youtube.com/s/player/e3cd195e/player_ias.vflset/en_US/base.js'; please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; see  https://yt-dl.org/update  on how to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.")); please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; see  https://yt-dl.org/update  on how to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.

Downloading manually added subtitles

 youtube-dl --skip-download --write-sub https://www.youtube.com/watch?v=vP4iY1TtS3s

Downloading only the automatically generated subtitles (in vtt format)

 youtube-dl --skip-download --write-auto-sub URL