http://www.youtube.com/watch?v=jVBcAcikn_4_
Alright we start with a galaxy which is important because it's the first image seen in the video, I would say that this sets the scene. The second thing I noticed was the flash of AC's symbol before it goes to what looks like a storm cloud. At 0:42 you'll see some Sentinels I believe and then at 0:43 you will see what I believe is the Greater Ark. It has 6 arms as described. It looks like it's open and is releasing some object. Next it skips to some blobs for lack of a better word, I don't know what they are, they look like cells. Next is this image of something of an hourglass shape, it reminds me of where the Monitors met in the Halo: CEA terminal. The image after that looks pretty important, it's an image that shows 2 grids which I think are the boundaries of real space and the in between would be slipspace or a different dimension. The helix shapes are most likely coordinates of some sort. I don't understand what the Halos' significance are of being there. Then we see something falling from the sky in a blaze kind of like Chief did at the beginning of Halo 3. At 1:30 we see what looks like a Flood Stalk or part of a Flood Stalker form. I think it is Flood because in the bottom left there you see the red feathery things that are found on the tops of Infection Forms. And the rest of the video is just a blue screen of binary code that probably has some meaning but I'm not willing to find it out.
It looks like the Greater Ark is inactive in the video because the pillars of plasma it uses to light it are not activated but there is an outside light source.