Freak tried tweaking it a while back and it's changed since then.
You have to add the S to the HTTP
You do the regular [youtube] [/youtube] tags with the youtube link in the middle but you have to add the S to the HTTP. Ex: [youtube]https://www.youtube.com/watch?v=0TtljBYGDlQ[/youtube]
So if you find an old thread with Youtube links in it that used to work and don't now that's why.