343 Industries is putting together a webseries that follows the chronicles of the Human-Covenant War which they plan to put out in episodes leading up to the release of Halo 4 in November 6.
Halo 4: Forward Unto Dawn is set before the events of the Halo games and follows the experiences of a young cadet who becomes one of the leaders aboard the UNSC's greatest spacefaring ship, the UNSC Infinity. He is said to have been inspired by his encounters with the Master Chief.
The live-action series is being developed with "top Hollywood talent" to deliver a brand new Halo story and flesh out the already expansive universe. It is expected to go live this coming October on the Halo Waypoint as a five episode series, and through YouTube on the Machinima channel.
Microsoft has announced that the Limited Edition of Halo 4 will also include access to the Special Edition of "Halo 4: Forward Unto Dawn" which includes additional footage, fiction, and behind-the-scenes content.