We cannot say with 100% certainty that this video is legit but sure looks that way. It contains footage of the Halo: Reach boot-up process and gives a glimpse of  informative text about “murder mod”. Bungie has definitely taken some notes on the hugely successful Modern Warfare series.

No source is given but the images seem to have stemmed from allgamebeta.com. All images carry the EB Games logo in the bottom left but it seems that the EB Games websites doesn’t mention the images.