Pretty much what the title says, trying to figure out what song they have playing in the trailer. If anyone knows, lemme know please. 
The song is from the Halo 4 OST.Track 10. “To Galaxy”
Here’s a link
The part from the trailer starts at about the 2 minute mark.
It might not be the EXACT song but it sounds extremely similar. I was listening to both the track and the trailer back and forth for a bit. May be a remixed version or something. Sorry about not naming the EXACT song. 
> It’s actually To Galaxy (extended)
>
> http://www.youtube.com/watch?v=TmAPACP5nPM 5:20 —>
This. Specifically the last 2 minutes or so
Excellent, thanks!