Halo Online Announce Trailer
From Halopedia, the Halo wiki
The Halo Online announcement trailer was released on March 25, 2015. It showcases gameplay (including the sandbox and several maps) as well as the armor and weapon customization menus. The trailer is set to the Halo Legends track "Sacred Icon Suite 2".
As this trailer uses a Pre-Alpha build, many graphics and names are not final.