From Halopedia, the Halo wiki
ONI Archive is a video content series tied to Halo: The Master Chief Collection's release on PC. The series consists of a number of trailers designed to recap the the general outline of each game in the collection's story and prepare new or returning players for jumping in to each game's campaign. Each video is framed with an in-universe narrative, with the videos presented as a series produced by Section Two of the Office of Naval Intelligence, aimed at educating civilians on the final months of the Human-Covenant War.
Noble Endeavours was the first video produced in the series, launched to celebrate the release of Halo: Reach within The Master Chief Collection on Xbox and PC platforms. The video centers around NOBLE Team and the Battle of Fumirole, leading into the Fall of Reach.
Conflict Evolved was the second video in the series, launched to celebrate the release of Halo: Combat Evolved Anniversary as part of the collection for PC. The video centers on the actions of John-117 and the Battle of Installation 04.
Changing Tides was the third video produced in the series, launched to celebrate the release of Halo 2: Anniversary on PC. This video discusses John-117 and the Battle for Earth, though mentions little of The Arbiter and the later events of the game.
Allied Forces is the fourth video in the series, released to celebrate the launch of Halo 3 on PC. This video discusses the Battle of Installation 05 and the Great Schism, leading into the events of Halo 3.
Reclaiming Our Place
Reclaiming Our Place is the final video in the series, released for the launch of Halo 4 as the final game in being added to the Master Chief Collection on PC. The video focus over the UNSC actions on the battles on Installation 00 and Installation 08, the post-war era, and the start of the Battle of Requiem.
In keeping with the in-universe framing of the video series, the videos contain their own narrative audio drama. At the end of each video, starting with Conflict Evolved, the final part of the trailer is cut off with a "Transmission Interrupted" notice, and a short audio snippet is heard. The audio drama centres around Director Schaefer and a unnamed Comms Officer working within ONI, and features numerous nods to other pieces of fiction with the mention of characters like Michael Sullivan. In Allied Forces and Helljumpers, the Comms Officer comes across upon some new - presently undisclosed - information, which is soon followed up by Codename: FIXER. This meta-narrative presumably ties into the upcoming Halo Infinite.