Tech question on demos

[VaeVictis]

So I'm bored and been meaning to post a thread on it just cause i am curious and it has been bugging me

I obviously am not a person who has dissected any quake source code or really coded a lot of games so i have to ask

How does a demo actually work? what does it record? how does it play back perfectly?

[[BTF]Sigma]

!ZING!

All aside, great topic

I'm guessing it replays what the client is doing and what the server is sending to the client. I think it has something to do with the timing of packets.

Again, good topic.

[VaeVictis]

!ZING!

All aside, great topic

I'm guessing it replays what the client is doing and what the server is sending to the client. I think it has something to do with the timing of packets.

Again, good topic.

well i was thinking something like it saves cmds run through the engine and just replays the game because all the values and stuff should make the round play exactly the same... but then i thought, quake2 also has random variables and stuff :/

whats really interesting to me is how the file size is so tiny for demos compared to movie files, i know its mostly because it doesnt really have to render anything, but there has to be more keeping that file size down

[[BTF]Sigma]

It's simply data that the engine uses to rebuild the recorded section of the game. (afaik)

I'll try to explain it this way.

Imagine you've gone and bought an IKEA desk with all the attachments. You open up the box and look at the instructions. They may simple and straightforward, yet the task of actually assembling the desk can take a while.

Now, the instructions are actually the *.dm2 file. The assembling is done by your client. The video of a demo is just like someone recording you following the instructions.

Does this analogy make any sense? I think I may have been quite blunt.

[reaper]

http://tastyspleen.net/quake/forums/index.php?topic=2629.0

Some of this was discussed in this thread.  It seems basically the demo is the information the server sends the client.  Keygrip takes this information and shows it frame by frame and allows editing, a quake2 client replays it for you.

[VaeVictis]

so.... a demo is basicly the frames of data visible that were registered on your client, and then you play the frames back with your client from a dm2 file and it smooths together just as if it were rendering the normal game

that right?

does that mean if i up my cl_maxfps i get a larger file size for my demos? o.o

[[BTF]Sigma]

Not sure how those mesh together

[QwazyWabbit]

A very good question.

A client demo file contains the initial state of the client, the map file name, the models in use and initial data it needs to start the playback from the moment the data record begins, then it contains a record of the frames received from the server by the client that made the recording. The server frames come at a fixed rate of 10 frames per second so I don't think the cl_maxfps has any bearing on the file size. The length of the file will merely depend on the intensity of the action and the duration of the recording.

A video record of a playback of a demo is a set of screen captures of the image of the played demo file. The skins, models and environment will depend on the client used to play it back, not the client that made the demo.

R1q2 clients using protocol 35 record more information than an original Q2 v 3.21 client would when using protocol 34.