I think the 13 e3 trailer is from halo 5. If you read the comics chief is getting signals or a small fragment of cortana or something like that. He follows the signal and finds the gravemind rebuilt on the arc from halo 3 but the gravemind gives him the data chip from the trailer to locate mendicant bias so he can help undo cortanas rampency. The giant bird thing is a sentinel operated by mendicant bias and all of this takes place right after halo 4 apparently. Halo follower has a video on it so it would make more sense if u watch it.