Embedding still fetches from YT.
Archive offline - what Q says…
youtube-dl is a good command line tool that usually works for me - the best I've found
This is probably a topic that needs more attention, to be honest… I'll say what I do for my own use, but others probably have different methods.
I'd say that if Q or anyone posts a link with a video that you need to archive, there are really two crucial things to do: grab the overall image of the page and the video itself.
For the page image, I find the FireShot extension works well. It is available on multiple browsers. Sometimes I'll just capture the whole page or sometimes I'll crop out stuff that is obviously appearing due to my own cookies (like on YT). But make sure not to miss any data that might be relevant even you don't know how.
As for videos, I like youtube-dl.
https://ytdl-org.github.io/youtube-dl/index.html
I use it from the command line and find it much more effective than online services for this. You can get a list of files sizes with the flag -F (at least on YT). It works for many, many sites. Sometimes you'll need to inspect the source to find a m3u file and then pass that to the command. I've had to do that on a few of the vids Q linked I think. That is only needed of the actual video is divided into multiple files (but that is not the case on youtube).
youtube-dl is packaged with many linux distros and in any case anyone should use caution when installing software - if I sound like a shill DON'T go installing a windows executable!
If I were archiving a news article that Q links to, I would go further and capture every link that might be in the main article. So basically I would archive at least two levels deep. Q has posted many "background" articles that have crucial info gained via the inner links.
Some missing links that Q has posted are available via archive sites. For instance, I have had success finding /r/greatawakening posts on archive sites even though reddit deleted it.
Some "missing" Q links are likely available via qresear.ch.
Another useful tool for archiving is the "Web Developer" extension. (I'm talking about the extension not built-in functionality." The crucial thing is it allows you to turn off all CSS with one click. This can help you find files that may be obfuscated and it works to undermine most paywalls, since they mostly seem to just overlay the main article with other html elements. Turning off CSS lets you see EVERYTHING even though it looks like crap.
Also, twitter works with youtube-dl. If POTUS posts an "interesting" vid I usually aim to download it asap since they often delete it and even the Q archive sites won't have the vid even if they've got the tweet.