So up until now, the Master Chief Collection had prevented us from being able to watch film clips in theater mode with friends over Xbox Live for whatever reason, even though Halo 3 and ODST on the Xbox 360 did in fact support multiplayer theater mode. Well, much like the removal of soundtracks in cutscenes, Halo 3 and ODST actually still retain a lot of their theater mode code and I found a way to enable multiplayer in theater on the Master Chief Collection for Halo 3 and ODST. Unfortunately, it doesn’t work with Halo 4 or Halo 2 Anniversary (based on Halo 4) because those games never supported multiplayer in theater mode to begin with on the Xbox 360. Anyways, here’s the video tutorial for how to watch film clips in theater with your friends.
Enjoy! There are a few other interesting side effects to it too such as accessing limited Forge controls in campaign. But as you can see, multiplayer theater mode works perfectly fine on MCC so I have no idea why 343 decided to disable that feature.