Demo

A demo is a recording of a game session that can be played back using the game engine.

Built-in demos
If no menu selection is made after launching vanilla Doom, three built-in demos soon begin to play repeatedly, evoking an arcade game. The demo levels are: When a GUI launcher, such as the Doom95 front end, is used to start the game, the launcher usually warps to a selected level and the built-in demos are bypassed.

The built-in demos are stored in lumps in the IWAD file named DEMO1, DEMO2, and DEMO3.

Player demos
Players can record demos of their own game sessions. This is done using the -record  command line argument, which places the recording in a file named  .lmp in the Doom program directory.

A recording can subsequently be played back using the -playdemo  command line argument, where  .lmp is the name of the recorded file.

This recording facility allows players to compare their skills in single-player mode (see Speedrun). It is also possible to record multi-player games.

Demos can usually be played back only with the source port used to create them. See LMP for additional details.