.DEM File Extension

A DEM file is a game replay file created by various first-person shooter games and most popularly by Counter-Strike (supported by Valve's Source game engine). DEM files are used to record a player's perspective in a single or multiplayer game, which can then be shared with others.

To play a Counter-Strike DEM file in Windows, first place it in the cstrike\​ installation directory. Next, start Counter-Strike and open the console window. From the console window, type viewdemo demoname, where "demoname" is the filename without the ".dem" extension.

DEM files are also used by Hexen II and Quake. A separate subset of DEM files are used by Unreal Engine games, such as Unreal Tournament. However, the files are only playable on the game for which the demo was created.

NOTE: DEM files created by Source engine games, such as Counter-Strike, can be opened in VirtualDub to play the video frame sequence and record it to other output formats, such as .AVI. There is a size limitation of 2 GB for AVI videos created by Valve's source engine. You can install the Apple QuickTime component to encode the .H264 codec in order to avoid the size limitation.

A DEM file contains a dataset detailing land contour in the Digital Elevation Model (DEM) format. It stores raster data in plain text format, with each pixel representing an elevation value. DEM files often store information about the terrain of planets, asteroids, or moon terrain.

The United States Geological Survey (USGS) develops the DEM format, but it is an open standard. Various GIS-related industries, including engineering, land surveying, urban planning, and scientific research, use the format for modeling landscapes and cityscapes. For example, a DEM file may contain elevation information for areas on Earth that include mountains, valleys, mesas, and sea depths.

The DEM format includes text blocks organized into three categories:

• A - Appears as the header in the DEM file, storing the origin, type, summary statistics, and the measurement systems the profiles used.
• B - Also known as the profiles, which store the elevation data and is the main section of DEM files.
• C - Stores root-mean-square error (RMSE) data referenced to measure the quality of the data

You can open a DEM file with various GIS applications, including ESRI ArcGIS for Desktop (Windows), Golden Software Voxler (Windows), and TatukGIS Viewer (Windows).

A DEM file may also be a video game replay created by a game that uses the Unreal Engine, a game engine developed by Epic Games. It contains data used to play back a recording of a player's gameplay. DEM files are created and played using the Unreal Engine's Console, which can be accessed by pressing the ~ key while playing a game.

The Unreal Engine gives game developers and players access to Console commands that allow them to record, play back, and examine their gameplay. For example, developers who want to check their games for bugs may want to record their gameplay to note when, where, and how bugs arise, and players may want to record their gameplay to note play mistakes and help themselves improve. To begin recording a replay within an Unreal Engine game, players can press the ~ key to open the Unreal Engine Console and enter the command demorec yourdemofilename. This will create a DEM file.

To stop recording a replay, players can enter the command demostop. Players can then play their DEM file by entering the command demoplay yourdemofilename. (Do not include the .dem extension as part of the filename.) If you forget your DEM file's filename, you may be able to find it by looking in your game's Saved directory, which is often used to store DEM files.

NOTE: All games created with Unreal Engine 4 include the Replay System used to create DEM files. Games created with earlier versions of Unreal Engine may or may not include the Replay System, depending on the game. Unreal Tournament does include the Unreal Engine Console and Replay System.

You can play a DEM file in the Unreal Engine game that created the file. For example, if you created a DEM file while playing Unreal Tournament, you can play that DEM file by opening the Unreal Engine Console in Unreal Tournament (by pressing ~ while at the game's main menu) and entering the command demoplay yourdemofilename. (Again, do not include the .dem extension as part of the filename.) Some third-party programs, such as UT Demo Manager, can help players more easily open and play DEM files in specific games.