What's up with YouTube's tail?

For the past couple of days, I've noticed that whenever I post a YouTube video it comes with a tail directly under the video that looks like this:

&pp=ygURQ2hlciB3b3JraW5nIGdpcmw%3D

Anybody know why YouTube is doing this?

I believe it's usually to identify what kinds of pages people are coming from, so they can analyze how people use the site. IE: do they mostly come to videos through channels, or playlists, or search, or whatever.

I've "collected" a bunch of those and I update the parser on our end to strip them out automatically, but there's always new ones or edge cases it doesn't have, unfortunately. But a lot of the most common ones disappear when posted here.

I guess it's something new YouTube is doing because it didn't happen prior to a day or 2 ago.

I can confirm YouTube has been adding stuff like this to URLs for many years. The code I mentioned above to strip it out was created quite awhile ago, and it's been added to many times since.

I think you're noticing it now because they've added some new ones I haven't accounted for yet, whereas in the past if you pasted a URL with extra stuff the site mostly just got rid of it automatically.