oops.... I've managed to mess up the YouTube embeds on the board.
I accidentally deleted the BBCode for 'youtube' and when I re-added it, all the old posts no longer have YouTube videos automatically embedded
The solution is to go in to each post and edit it and then click save. Nuts. That's going to take ages. Sorry namesinspace!
With this new theme it also seems to cut off the YouTube videos when you resize the browser. The Soundcloud one works nicely though, and I think images in threads will work too. Just need to figure out how to make YT ones responsive.