What we're looking at is a slice through a Mach 6 flow from left to right. The large white blob on the bottom is the top half of the vehicle body (the bottom half is below the video, but it's symmetric). The little white slice coming in from the right is the other part of the inlet (the "ring" part you see when you look at supersonic inlets). The giant purple line from lower left to upper right is the shockwave coming off the nose of the vehicle.
It's running nicely, then they close the throat a little bit and *wham*...unstart.
Not sure how much folks care about the underlying physics, but it makes for a darn pretty video.
I'm about 3/4 of the way through my masters in aero engineering (working at it part time). This week happened to be hypersonics, and the guys who did the CFD behind this video are collegues of my propulsion prof.