From what I've read of people suggesting that others use Camtasia or Fraps to record demos, am I to assume that there is no built-in functionality in jMonkey Engine?
Why would there be?
it would require huge amounts of memory to store the scenegraph changes per frame. and i cannot be done any other way because jme cannot know how the logic of the game works it's being used by. (offtopic: is this grammar valid?)
Darkfrog, the purpose would be so that you could have an interactive replay (viewing from an independent and controllable point of view), rather than just a video to replay.
HamsterOfDeath, do you have any idea how this is done in Unreal Engine?
(I think your sentence worked fine except that I would move "works" to the end of the sentence . . . for extra credit you could say, "how the game logic built on top of the engine works.") 
Thanks for the answer!
My bad, I assumed you meant capturing video from within the engine.
This wouldn't be too difficult to write I don't believe. You could create a custom Controller that gets added to your root node. The controller can be given a refresh rate to run and a list of Spatials to validate synchronization with. This will keep you from having to walk the entire scenegraph, but allows you to keep a good validation of the objects that you want to monitor. It could record these changes to a file that could later be replayed with another custom Controller that similarly registers the objects. If I had more time I'd be interested in writing this…sounds like fun. 
If you have a networked game, you could capture the network traffic into a file, then you could feed it back into the game.
Could you not use JGN running a local server (localhost) and utilize the sync capabilities already in place? Write a hook on the server side to dump all that info into a file. Then reconnect to the server in "playback" mode and have it feed you the data from the file once again using the sync capabilities already in place?
Is this crazy?
vear said:
If you have a networked game, you could capture the network traffic into a file, then you could feed it back into the game.
Dammit! It said there was a new post while I was writing mine - shoulda went and read it :D
hehe…unfortunately I still have 0 time to spend on this stuff lately, so it's still not cut down enough.