I get this error: "can't convert undefined to object"

2020-02-08: Still working great BUT... [published_date] tag has now disappeared. How to get it back?

2019-12-22: This time, it really is HOORAH! I got it working! On a whim, I clicked on the ffmpeg button in Settings (where it says "installed"). Well, it came up with another executable, so I saved it to my ffmpeg folder, and presto! Now it combines audio and video with no backtalk. Beautiful!

There are two little glitches: a) sometimes the previous video is saved, instead of the current one. I just have to remember to F5/Refresh before firing up the downloader; and b) as mentioned here somewhere, many characters are flagged as invalid and replaced with a dash. This is the case for parentheses, apostrophes, square brackets, etc. There's really no need to replace those. I'd rather have the original characters and be told by the OS that they're really and truly invalid.

*** All in all, a solid 5 stars now that everything is working. Perhaps I should be getting the three stars (or less!) for not figuring this out sooner.

2019-12-22 (earlier): Hoorah! Sort of... I updated to the latest version (0.8.9) released yesterday and I no longer get the "cannot detect url_encoded_fmt_stream..." error. I've re-installed the latest versions of native client (NodeJS) and ffmpeg, the connection says it works. HOWEVER, when comes time for combining, I now get a "something went wrong" message asking me if I'm sure native client is installed, blah, blah. I can combine manually (with ffmpeg at the cmd line) but it's a major pain, especially knowing that this should happen automagically. I'm bumping up my review to 4 stars; if I can figure out how to get it to work (or if some helpful Samaritan can point me in the right direction; anyone, please), I don't see why I wouldn't give this great add-on a 5 star rating. Here's to hoping...

Oy! I almost forgot to mention: the date_published field now works. That's fantastic! Much appreciated.

2019-12-19: Well, now it's useless. YouTube videos by the dozen are showing this error. So YouTube Video and Audio Downloader (WebEx) is of little use. As mentioned previously, Video DownloadHelper is no better, because often the only format to save to is webm; I prefer mp4. I realize this is probably a change on the YouTube side, perhaps to prevent downloads, and not a true failing of this app, but the result is the same. Is there any way around this, or might the app be updated to do so? Thanks, and sorry for the negative comments but that's the long and short of it. Thx

My previous review/comments:
2019-12-12: This was an awesome downloader until a few weeks ago, when I began getting "cannot detect url_encoded_fmt_stream_map errors on some videos. Sometimes, rarely, a refresh (F5) clears it up. Stuck using Video DownloadHelper, which is sub-par. Any chance of a fix? Thx

Better than all other YouTube downloaders. It keeps things simple. YouTube now streams separate files for HD video and audio. This addon uses ffmpeg (trusted open source video software) to thread the video and audio together and give you a complete result. No weird registrations required. The plugin parses all the available different video and audio qualities for you to chose from. The only downside is you must go into the plugin options to install the native client and ffmpeg, but that's easy as downloading and running a bat file and pressing an install button.

No MP3 download possible, you would have to convert cumbersome.

It at least works, which is something that most other YouTube MP3 format downloaders don't do. But even when I requested an MP3 file, it downloaded the video in MP4 format, and it did so at a very low bitrate, making for a sub-par audio line. Would not recommend.

working good

Very nice.

POWERFUL TOOL for Firefox. THANK YOU!!!!!!!!!!!

"Auf Ihre Daten für alle Websites zugreifen

Die Erweiterung kann sowohl den Inhalt jeder von Ihnen besuchten Webseite lesen als auch die Daten, die Sie dort eingeben, z. B. Benutzernamen und Passwörter. "
No thx!

Seems to work sometimes. Not terribly bad.