Here's a warning right off the bat that the leaked internal beta footage for Halo 4's multiplayer that is the subject of this post is blurry and largely unwatchable. It's also saddled with very NSFW music, so you'll have to dig up the video elsewhere on the Internet. Perhaps from one of our source links (HINT, HINT).
The footage was discovered by NeoGAF, with a subsequent update from Microsoft all but confirming the video's legitimacy. As the publisher told Kotaku, "We are conducting an internal beta test of Halo 4 which is a standard development practice for most video games. We have no plans for a public multiplayer beta for Halo 4."
There's plenty of discussion unfolding in the NeoGAF thread about what's happening in the video. You get a look at the new Railgun, Promethean vision (that lets players see through walls), assassinations and more. Just don't blame us if you watch the eight minutes of footage and walk away with severe eye strain.