Found this posted at Neogaf, video might be gone by morning.
First - Turn your speakers down. WAY DOWN.
Second - This has to be leaked by MS or whoever is working on the game now. If not someone is attempting career suicide.
Third - The footage looks real. Go two minutes in for actual footage.
Now here is the catch and if this was leaked, it is the greatest leak ever.
It is played on a farm, using a SD television, calling it a VHS release, though it looks closer to something you would get from a mobile phone.
http://www.youtube.com/watch?v=BPhhb1gidPg#ws (http://www.youtube.com/watch?v=BPhhb1gidPg#ws)
It's real, known changes are in the video. The fact that it's still up at this hour makes me think it's marketing.
This will be a very polarizing release;killstreaks,killcams and shields will upset Halo vets.