This is the most consistently reliable add-on for downloading YouTube videos and doesn't rely on external conversion sites or extra software. Occasionally, there will be some update (usually on the YT side) that breaks the feature but the developer is impressively responsive in fixing the issue. One of my must-have add-ons.

I, too am seeing the illegal character bug. As with all such problems (see below), it started with a couple of videos, and is spreading like...well, that disease. Clearly some kind of service rollout. Hope the author can fix it.

To those who complain about it not working: there is a constant cat-and-mouse / whack-a-mole game between this plugin and the Tube. Youtube (purposely) breaks it, author fixes it. Wash, rinse and repeat.

So please cut the @feller some slack. However, *DO* report errors you are seeing. Try to be as clear as possible: the clearer it is, the sooner it will be fixed.

App shows "Filename must not contain illegal characters" constantly, when all characters are very common A-Z letters, & I never even changed anything to begin with. This is an awful app: it has a simple purpose, & just won't fullfil it at all.

Error messages, when the only thing I click is to download, is unacceptable.

Szar

I have used this add on for quite some time with no issues and great results....until today. When I open the download panel is just states file size and UndefinedK. What does that mean and how do I fix it?

Great inteface. Easy to use. Uses the library for download progress.

There is an error when combining audio and video files: "cannot find the file". Ffmpeg and software are installed correctly.

May 11 2020, it's working again!
Jan 12 2022, stopped working. Went back to earlier version, but now it doesn't combine files.
Dec 2022, not combining files. Looking for something else. March 23, no longer combines audio and video.

This is a great add-on. I have used it for years to extract videos for my prison ministry. However, like Devilshaker, it has stopped working for me. I also uninstalled and then reinstalled the add-on. This worked that last time I encountered the cannot detect url_encoded_fmt_stream_map... but not this time. Perhaps the developer has not yet fixed the current version for this occurance of the problem. I hope it gets fixed soon.

not bad seems to get the job done.