Steps to replicate the issue
[[File:Ubisoft Quebec office.webm|thumb=Ubisoft Quebec office in 2013.jpg|Ubisoft Quebec office in 2013]]
What happens?
Inserted object is 1200px wide and can't play video. Does not respond to upright=0.5 or 220px parameters.
What should have happened instead?
According to TheDJ this is a regression so it should probably do what it used to do..
Oh, what I wanted is actually possible, it just wasn't documented on https://www.mediawiki.org/wiki/Help:Images. (I added it now)
[[File:Ubisoft Quebec office.webm|thumb|thumbtime=26|Ubisoft Quebec office in 2013]]
And according to @TheDJ the other thing is a bug.
It seems my memory was mistaken. This never worked for videos.
The sizing is also a know thing and documented as such on en.wikipedia:
With an operand, e.g., "thumb=Example.png", the operand names an image that is used as the thumbnail, ignoring any size specification.
https://en.wikipedia.org/wiki/Wikipedia:Extended_image_syntax
I think this is honestly part of the whacked image syntax features that MediaWiki 'accidentally' provided in 2004'ish, but that really needs to be rewritten and thought out a bit better for modern days :(