Destiny doesn't seem to be sending any more data than Halo did. Bungie has had a brilliant theater plan ever since Marathon, and I miss it terribly. I think my friends and I spent more time in Halo 3 watching replays in slow motion than we did actually playing the game. Also, with Destiny's graphics, a theater mode would look absolutely fantastic. And then they could do little slow-mo montages at the end of each match showing the best kills. And, you know, kill cam could be a thing, which should totally be a thing, because kill cam is a good thing for showing people that they didn't actually get shot through a wall and around a corner.

For those who are curious: Marathon (and halo, later) just kept a log file of every action, and then in theater mode it played the log back. So the animations were all rendered in real-time while you watched, but the actions taken - shots fired, jumps, etc.. - all matched the game you were viewing. This is also why Halo could have slow-motion without you seeing the individual frames of gameplay stuttering by.

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(Ah wait, I'm supposed to demand that Bungie add something like this to the game...)