Hi, this is a newer method to achieving first person view in theater mode. I've sort of updated this tutorial but it might need a bit more work.
I did make some notes (mainly for myself) on how to do it.
Generally speaking you should use Peek Poker and just find the following patterns in a certain address range.
I can't guarantee this will work for you.
Link to my notes
You'll need:
Peek Poker.
xbdm plugin for peeking and poking.
Your Xbox 360, connected to your local area network.
This is mainly for Halo 3, however I have tested it (albeit with different patterns) on Reach & Halo 4 too. I haven't tested ODST but it should work.
Basically go into the theater lobby and start a theater film. Make sure you're in first person view on your own character. Don't change anything.
Leave the film and go back to the theater lobby.
In Peek Poker, connect to your Xbox IP and click on Search
For the start offset, put the start offset from the notes for the game you're attempting to get first person theater camera. For Example, Halo 3 is "C5000000"
In length put the length in. In Halo 3's case it's "02000000".
In the search for box, put in the values for the Default Theater state in Theater lobby menu. Halo 3's is "ec 70 00 00 00 00 00 00 00 00 00 03"
After hopefully getting some results, right click the offset, preferably highest one to the top first and click copy.
Click on "Peek & Poke" and in the address paste the offset and click peek.
Start your theater film.
Change to another player then click peek on Peek Poker, you should see some changed values in red.
Underneath 0B in Peek Poker (if it's laid out the same) change the 00 to 03 and click poke.
Again in Peek Poker, look at the current player being spectated (2nd 00, but could also be 05 or anything else) observe current value then poke 00 (or a value of another player) then restore the original observed value.
The camera should now be in first person.
Enjoy!
I'm hoping to make a video at some point on how to do this, just so you can see what I'm doing when I do it.
Some things to note:
You'll need to peek and poke again if the target gets into a vehicle such as a warthog.
The viewing experience is better in campaign games than multiplayer games.
The pattern is different in Reach and Halo 4, refer to the notes for the patterns and search range.
Be careful poking, if you poke the wrong area or poke to a player that doesn't exist it'll crash the game.