Here we see a spartan preparing to jump off an object that is speculated to be something akin to a portable mancannon; an air lift similar to those found in Halo 2's multiplayer levels Warlock and Foundation, but in a piece of equipment that can be carried and deployed by a player.

Such equipment would appear to be one of Halo 3's major changes, compared to the previous games. At least two pieces of equipment are shown in the video and specifically referred to: the bubble shield (as seen in the "Starry Sky" CGTV ad from late 2006) and the tripmine, shown later in the VIDOC.

Frankie's post in the NeoGAF forum indicates there are an unspecified number of additional pieces of equipment; the air lift shown here may be one of them.