If you are okay with the command line, there's the (in)famous https://github.com/ytdl-org/youtube-dl.
See https://github.blog/2020-11-16-standing-up-for-developers-youtube-dl-is-back/ for backstory.
From: Code for Libraries <[log in to unmask]> On Behalf Of charles meyer
Sent: Sunday, April 4, 2021 1:59 PM
To: [log in to unmask]
Subject: [External] [CODE4LIB] You Tube downloader
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Hi my esteemed listmates,
I need to watch educational webinars offline many times.
I've been using the Ant Downloader with Firefoc but once the video download when I play it in VLC Media Player it just play the audio, not the video.
I've also used (but it's not working last 2 days) youtube-GUI.
Have you found a program which downloads webinars on YT and one which will then play that video offline?