I've been using this for years!
Since the new YouTube embeds, lots have changed, But...
The HD-on-auto fix mentioned here works on 6.4.4 but not 6.4.5
Also, on 6.4.5… The info and share button shows even without the settings not being active.
On the top right…. They are not activated!
In the html, i am guessing this is the script that does the job.
But it has a big bug! First off, right after the link, there is no ?, it just goes to using &, which is invalid!