View source for DEM (file format)

{{otherlang2
|ru=DEM_Format:ru
}}
''DEM'' (short for demo) is the Source demo file format. Used in conjunction with the Source recorder to record demos.

{{note|it is not possible to edit what happens in a Source demo after the recording, it basically stores the packets right off the wire and we don't know the packet format}}

For the purpose of this we will be referring to each collection of events as a frame. This may or may not add up to the number of frames given by the header.

===Demo Header===
{| class=standard-table
! Type || Field || Value
|-
| [[String]] || Header || 8 characters, should be "HL2DEMO"+NULL
|-
| [[Int]] || Demo Protocol || Demo protocol version
|-
| [[Int]] || Network Protocol || Network protocol version number
|-
| [[String]] || Server name || 260 characters long
|- 
| [[String]] || Client name || 260 characters long
|-
| [[String]] || Map name || 260 characters long
|-
| [[String]] || Game directory || 260 characters long
|-
| [[Float]] || Playback time || The length of the demo, in seconds
|-
| [[Int]] || Ticks || The number of ticks in the demo
|- 
| [[Int]] || Frames || The number of frames in the demo
|-
| [[Int]] || Sign on length || Length of the signon data (Init for first frame)
|}

===Frame===
Each frame begins with 0 or more of these commands:
These are described in hl2sdk\utils\demofile\demoformat.h / hl2sdk-ob\public\demofile\demoformat.h / hl2sdk-l4d\public\demofile\demoformat.h

====Network Protocols 7 and 8====
{| class=standard-table
! Type || Value
|-
| dem_signon || 1
|-
| dem_packet || 2
|-
| dem_synctick || 3
|-
| dem_consolecmd || 4
|-
| dem_usercmd || 5
|-
| dem_datatables || 6
|-
| dem_stop || 7
|-
| dem_lastcommand || dem_stop
|}

====Network Protocols 14 and 15====
{| class=standard-table
! Type || Value
|-
| dem_stringtables || 8
|-
| dem_lastcommand || dem_stringtables
|}

====Network Protocols 36 and Higher====
{| class=standard-table
! Type || Value
|-
| dem_customdata || 8
|-
| dem_stringtables || 9
|-
| dem_lastcommand || dem_stringtables
|}

Depending on the command that was received, a different action needs to be taken.

====dem_stop====
This is a signal that the demo is over, and there is no more data to be parsed.

====dem_consolecmd, dem_datatables, dem_usercmd, dem_stringtables====
Read a standard data packet, deal with it as necessary.

====dem_synctick, dem_signon, dem_packet====
Ignore.

===Standard Data "Packet"===
Any time there is more than one byte to be read in, a standard format is used.

This begins with an integer that has the number of bytes in this packet.

Example code to handle this:

<source lang="cpp">
int ReadData(char **buffer)
{
	int len;
	fread (&len,sizeof(int),1,fDemo);
	if (len > 0)
	{
		*buffer = new char[len];
		fread(*buffer,len,1,fDemo);
	}
	return len;
}
</source>

=== Frame Format ===
<source lang="cpp">
Frame {
       int ServerFrame;
       int ClientFrame; //ServerFrame and ClientFrame delta probably correspond to client ping.
       int SubPacketSize;
       *buffer = new char[SubPacketSize]; // State update message?
       Packet pkt = (rest of frame as data exists) // All demo commands are strung together in this area, structure below
       JunkData data = (unknown) // ex: 0x8f 5a b5 04 94 e6 7c 24 00 00 00 00 00 ... (40 bytes of 0x00 after the 0x24)
                                 // This could either be the end of the frame or the start of the next frame.
}
</source>

<source lang="cpp">
Packet {
       char CmdType;
       int Unknown;
       int TickCount; //This only sporadically appears.
       int SizeOfPacket;
       *buffer = new char[SizeOfPacket];
}
</source>

=== Example of use ===

It can be interesting to grab the header of the demo files in case you run a webserver which is hosting your demos / TVs.
Here is a PHP script that does the job for you, and has hability to tell you if the demo-file is a Record in Eyes or a TV.

You can easily convert it in a C++ code if you plan to use it for another need.

<source lang="php">
<?
/* Source & OrangeBox demos header reader.
By PoLaRiTy (nocheatz.com)

Help from   : https://developer.valvesoftware.com/wiki/DEM_Format#Demo_Header
              http://hg.alliedmods.net/hl2sdks/hl2sdk-css/file/1901d5b74430/public/demofile/demoformat.h

Types sizes :
Int : 4 bytes
Float : 4 bytes
String : 260 bytes
*/


class DemoInfo_s
{
	var $dem_prot;       // Demo protocol version 
	var $net_prot;       // Network protocol versio
	var $host_name;      // HOSTNAME in case of TV, and IP:PORT or localhost:PORT in case of RIE (Record In eyes).
	var $client_name;    // Client name or TV name.
	var $map_name;       // Map name
	var $gamedir;        // Root game directory
	var $time;           // Playback time (s)
	var $ticks;          // Number of ticks
	var $frames;         // Number of frames
	var $tickrate;       // Tickrate
	var $type;           // TV or RIE ? (0 = RIE, 1 = TV)
	var $status_present; // true if a status command is available in the demo.
}

function ExtOfFile($pathtofile)
{
	return end(explode('.',$pathtofile));
}

function ReadString($handle, $n = 260)
{
	$buffer = "";
	for($d = 1; ((($char = fgetc($handle)) !== false) && ($d < $n)); $d++) $buffer = $buffer.$char;
	return trim($buffer);
}

function ReadInt($handle, $n = 4)
{
	$buf = fread($handle, $n);
	$number = unpack("i", $buf);     
	return $number[1];
}

function ReadFloat($handle)
{
	$buf = fread($handle, 4);
	$number = unpack("f", $buf);     
	return $number[1];
}

function IsGoodIPPORTFormat($string)
{
	if(preg_match('/[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\:[0-9]{1,5}/', $string))	return true;
	else return false;
}

function GetDemoInfo($pathtofile, $fast = false) // BOOL fast : if true, doesn't check the presence of the status 
{
	$infos = NULL;
	if(ExtOfFile($pathtofile) === "dem")
	{
		$handle = fopen($pathtofile, "r");
		if($handle)
		{
			if(ReadString($handle, 8) === "HL2DEMO")
			{
				$infos = new DemoInfo_s;
				$infos->dem_prot = ReadInt($handle);
				$infos->net_prot = ReadInt($handle);
				$infos->host_name = ReadString($handle);
				$infos->client_name = ReadString($handle);
				$infos->map_name = ReadString($handle);
				$infos->gamedir = ReadString($handle);
				$infos->time = ReadFloat($handle);
				$infos->ticks = ReadInt($handle);
				$infos->frames = ReadInt($handle);
				$infos->tickrate = intval($infos->ticks / $infos->time);
				if(IsGoodIPPORTFormat($infos->host_name)) $infos->type = 0; // RIE   TODO : Add localhost:PORT check.
				else $infos->type = 1; // TV
				$infos->status_present = false;
				if(!$fast && !($infos->type == 1)) // No status in TV records.
				{
					while(!(($l = fgets($handle)) === false))
					{
						if(stripos($l, "\x00status\x00") !== false)
						{
							$infos->status_present = true;
							break;
						}
					}
				}
			}
			else
			{
				echo "Bad file format.";
			}
			fclose($handle);
		}
		else
		{
			echo "File not found or unable to read.";
		}
	}
	else
	{
		echo "Bad file extension.";
	}
	return $infos;
}
?>
</source>

[[Category:File formats]]