I always try removing the shit after the ? and if it doesn't affect the destination of the link at all then I assume it's tracking bullshit and in my opinion you should too.
you start to get a feel for when you can and cant remove everything after the ? and be fine, and occasionally even what specific parts are necessary and what can be removed
These will all appear after either a question mark, or an ampersand in the URL for further arguments:
- v=[bunch of numbers and letters]: Video ID. Essential to sharing a Youtube link for reasons you can probably figure out; do not remove. Only appears in this form on the main site (in the format
https://www.youtube.com/watch?v=[video ID]&[further arguments]) or on links shared by simply copying the URL on desktop; sharing from mobile or using the share button from videos will yield you a shortened link in the format ofhttps://youtu.be/[video ID]?[further arguments]. - t=[number, usually one to four digits long]: Timestamp, in seconds. Sometimes also formatted in hour:minute:second format as
[x]h[y]m[z]s. Can be safely removed if you want to link the video from the start, but you probably won't want to. - fmt=[two digit number]: Video quality; shows up mostly in very old links as a way to force high quality playback back in Youtube's early days. Does nothing these days.
- feature=: Internal tracking data for how you use their site, usually shows up as
feature=sharedon a video shared using the share button. Feel free to remove, but ultimately doesn't do much in most cases beyond tell Youtube you used this particular feature, I feel. - si=[bunch of numbers and letters]: As far as I'm aware, this is the personalized tracking bullshit. Either way, it sure is doing nothing useful clientside, so remove with great prejudice just on principle.
There may well be stuff I missed here; off the top of my head this is just what I've been able to think of.
EDIT: Further additions, thanks to @dzamie and @Starra mentioning them in the replies and comments:
-
pp=[bunch of numbers and letters]: As
si=, tracking nonsense. Given that it specifically shows up in URLs copied from the search page, likely connected to that somehow. Remove. -
list=[bunch of stuff] and index=[bunch of things]: Playlist functionality. Remove if you want to send the video by itself, keep if you want to attach the playlist you found it in; may break some external applications.