troels,
Had to say from the video. Emperors will often develop light colored spots in the area where there is a lesion - I think that is what you are seeing. Now, what is the original cause of the lesion - I can't say, but both flukes (trematodes) and Cryptocaryon will cause those sorts of pale spots on an emperor. Also, I couldn't time it, but the fish may be breathing a bit fast.
Jay