Doom 3 demos

How can I make an avi demo for a custom map? Does anyone know the step(s)?

If not that, how can I save a .demo file into an avi or mpeg?

Thanks in advance

Well, there's a few steps involved.

1. Enter recorddemo (filename) to record your desired demo.
2. stoprecord to stop the demo.
3. avidemo (filename) to create a series of .tga files from the demo. Each file is one frame from the demo footage.

At this point you will have a ton of tga files in your screenshots folder. What you will now need to do is use a program that will take all of these screenshots and turn them into a video file. I personally recommend Quake Video Maker. You can find it with a bit of googling.

Notes:
You will end up with a massive amount of HD space taken up. I hope you have lots. Also, by default, the tgas will be something like 320x240 resolution. to change this, use com_aviDemoWidth and com_aviDemoHeight to specify different resolutions. Finally, there will be no sound recorded with the demo. Because of this, I suggest using something like FRAPS or some other screenc capture program to record your footage instead of Doom3's built-in demo functions.