From Halopedia, the Halo wiki
The video takes the form of File:CHELAN_201903012, a file part of Director Schaefer's "content series" in ONI Section 2's public awareness campaign regarding the UNSC's role in colonial security. The series is aimed at educating UEG citizens on the history, evolution, and application of the Spartan Program.
ONI Screen activates, showing the file name "FILE:CHELAN_201903012, and a wave form of a "Comms Officer".
The filename is a reference to Halo: Reach's launch in Halo: The Master Chief Collection with the number "201903012" referring to the game's launch date of December 3, 2019. The CHELAN part of the name refers to the Chelan app that requests permission when the player logs into Xbox LIVE through Steam.