The scariest thing about this is that despite the social and economic conditions in North Korea, nobody really knows for sure if NK is possible of this sort of attack. It could be all bluff for all we know, but these seem to be pretty significant threats coming from a country that has increasingly in the last few weeks acted quite insane (threatening South Korea, posting this video, etc.).

Anyway, for those wondering, this video was posted on a semi-official North Korean website.