Recording Requirements

[Legend]

hi,
I've been wondering what would the requirements needed to have a console be able to record a game session- however long it may be- be.
Gran Turismo has been letting you record replays for a while now in a very very small file. I presume the game isn't actually recording the video but rather the inputs you made and thus re-creating the race each time you replay the replay.
but I'm not only talking about replays, I am talking about saving any part while you are playing a game. I gave the GT example as to maybe not have such a performance hit when applying such a feature.
this came more to my mind while seeing Halo 3 with its 'Forge' feature.

now, if I wanted such a feature to be default in a console (say PS3 or 360) would it only take a software update, or will it require hardware revision?

 

[ERP]

The short version is it requires the game to be written in such a way that recording a small amount of information is sufficient to reproduce the state consistently.

This is usually reffered to by developers as determinism, all games by definition are deterministic, however in this case we're refering to having deterministic results from a very small number of input variables. Usually just the joystick packets, although sometimes additional data like a clock.

In principle writing a game that lets you do this is easy in practice it's a really painful experience. In racing games we'd commonly see bugs where replays would diverge from original gameplay under obscure circumstances, and tracking them down was a pain.

We used to be able to record hours of racing in tiny buffers, we'd compress the joystick info on the fly as we recorded. In principle this can work for any game, and in the Genesis/SNES era would have worked for almost any game as written (XBand used to use this fact to hack network play into released games). These days most games aren't even close and would require huge time investments in time to make "replay" type mechanisms work.

 

[Colourless]

Typically if the game supports networking, it's not 'hard' to extend that to support recordings and playbacks (you really just record the network packets). Where things become tricky however is requiring the recordings to work between different versions of the game where the network protocol has changed. You just need to look at the likes of say the Quake games or Warcraft 3 where each patch breaks all the existing recordings/demos much to the annoyance of the players.

 

[Legend]

interesting. so what if we go with more of an actual recording of the video out put like a conventional tape/digital recorder, would that make things easier or will it strain the resources of the hardware too much that it will interfere with what is needed to run the game properly?

 

[archie4oz]

You can do it, but there's caveats... If you're talking something like PS3 or 360 it's doable although real-time becomes a bit iffy, but it's also not really required either (but doable if you got the cycles to spare). It's much easier doing it offline though (way back in the early PS2 days concocted a stupid little playback mode that could dump a game frame into a DV stream out to a camcorder)... But honestly it's not all that usefull when you can just hook up the console to a decent video capture device (and most PCs nowadays have plenty of poop for it).