Replay/Format details

The following is a detailed analysis of replay files as used in Grand Theft Auto: San Andreas. Due to similar programming, this article may be partially applicable to replay files for Grand Theft Auto III and Grand Theft Auto: Vice City.

Description
Replays are the sequence of the scenes and actions recorded and stored in the  file. In GTA San Andreas, this file is located in the User Files directory.

Each .rep file consists of a header string and variable amount of 'scenes' (or 'frames'). A scene is a copy of important game information at given moment of time (actors, vehicles positions, weather, clothes, etc). Following one after another, the scenes create an illusion of a movie when played. The most of scenes contains a same set of blocks and ends with Block 8.

The .rep file itself consist of a header string which is simply the text GtaSA29 and up to 8 parts, size of each one is 100,000 bytes, depending on the replay length. So, the maximum size of a replay file is 800,008 bytes (including 8 bytes of the header string). If the replay length is that it does not match 100,000 bytes boundary being less, the rest of the file is filled with useless data (commonly the previous replay data).

Data blocks
Each block consists of a byte denoting its type and some data as described below. A number in a block name is the data type stored in the first byte of the block. Reading this byte, the game detects what block follows.

Block 0: End of file
This block denotes the end of replay data. It consists only of a data type. After this block the game stops reading the replay file.

OFFSET TYPE      DESCRIPTION 0x00   byte      data type (0x00) 0x01             (end)

Block 1: Vehicle1
size 52 bytes

Block 2: Vehicle2
size 56 bytes

Block 3: Player data
Common information about player ped.

OFFSET TYPE      DESCRIPTION 0x00   byte      data type (0x03) 0x01   byte      index (handle?) 0x02   WORD      modelID 0x04   byte      ped type 0x05   byte[3]   (align) 0x08             (end)

Block 4: Ped
size 52 bytes

Block 5: Camera
size 88 bytes

Block 6: Day time
This block contains information about current day time during a scene. OFFSET TYPE      DESCRIPTION 0x00   byte      data type (0x06) 0x01   byte      currentHour 0x02   byte      currentMinute 0x03   byte      (align) 0x04             end

Block 7: Weather
size 8 bytes

Block 8: End of scene
This block denotes the end of the current scene (frame). It consists only of a data type.

OFFSET TYPE      DESCRIPTION 0x00   byte      data type (0x00) 0x01             (end)

Block 9: Scene timing
This block contains value of the global game timer. The replay play length could be found by using this block.

OFFSET TYPE      DESCRIPTION 0x00   byte      data type (0x09) 0x01   byte[3]   (align) 0x04   DWORD     timer 0x08             (end)

Block 10: Unknown
size 28 bytes

Block 11: Unknown
size 20 bytes

Block 12: Unknown
size 16 bytes

Block 13: Unknown
size 4 bytes; same as Block 8?

Block 14: Unknown
size 4 bytes; same as Block 8?

Block 15: Unknown vehicle
size 56 bytes; same as Block 2?

Block 16: Unknown vehicle
size 56 bytes; same as Block 2?

Block 17: Unknown vehicle
size 60 bytes

Block 18: Unknown
size 76 bytes

Block 19: Clothes
This block contains information on the current clothes of the player. The block structure is identical to the one in the Player structure in a save file.

OFFSET TYPE      DESCRIPTION 0x00   DWORD[10] modelCRCs 0x28   DWORD[18] textureCRCs 0x70   WORD      Fat 0x72   WORD      Muscle;

Tools
There is a template for 010 Editor, made by Seemann. It allows to edit different replay data: http://sannybuilder.com/dev/Replay.rar