The time signature of this song is a bit weird. I think it's mostly in 4/4 time with lots of split measures (2 chords in one bar), and a few 2/4 bars in between. But that doesn't really matter here.
So yes, if you have 2 chords with 2 beats each, the strum patterns I posted would stretch over 2 chords (4 beats).
(okay, if you're still on 8th note strumming, you may want to stop right here)
I believe there are also some "pushes" in there (I don't really play the song myself, so I'm a bit on my best guess here). "Push" means you anticipate the chord change by e.g. an 8th or a 16th, changing before the beat (usually on the up-stroke before the beat on which the chord change would otherwise happen).
If you want to really dig in and play the song "just right", the best option is to play along with CS again and again. Like many songs of his, this isn't following any set-in-stone patterns. He's changing things around a lot, improvising, and spicing things up in all sorts of ways (all of which is essential for this style of music).
I had a fresh peek at Justin's video just now, and you can copy that impro stuff from him as well (not surprisingly, since he's the Man
). One thing might be irritating for beginners though: when Justin plays simple Dududud, he actually plays D ud ud ud (for the theorists: touch of shuffle rhythm/swing time or down as dotted eigth and up as a sixteenth note). But before you start looking for high windows ledges (been there myself): the easiest way to learn this kind of rhythm is again to just play it. Stop thinking and lust play along. You can analyse it (much) later.
Bzw: if it's going too fast for any of you, use software so slow it down (many programs can do that without changing the pitch, I'm using Audacity for that kind of thing).
Man, I really need to learn that song myself so I can stop guessing