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Daniel Nylander edited this page Aug 1, 2026 · 7 revisions

File Formats

This page documents all file formats encountered in Captive and Liberation media.

PL5 — Captive DOS graphics

A PL5 image is exactly 40,000 bytes: 320x200 pixels at 5 bits per pixel.

Every 5 input bytes encode 8 output pixels using a bespoke bit layout (not a linear bitstream). The palette is not stored in the PL5 file — it comes from the corresponding ANM file header or a hardcoded VGA palette.

Decoding algorithm (C pseudocode):

for each group of 5 bytes (b0..b4):
    for bit 7 down to 0:
        pixel = ((b0 >> bit) & 1)
              | (((b1 >> bit) & 1) << 1)
              | (((b2 >> bit) & 1) << 2)
              | (((b3 >> bit) & 1) << 3)
              | (((b4 >> bit) & 1) << 4);

Output is 32-colour indexed. The renderer converts to ARGB via the loaded palette.

ANM — Captive DOS animation

Structure:

Offset Size Content
0 768 VGA palette (256 entries x 3 bytes, 6-bit RGB)
768 2 Command end offset (little-endian)
770.. variable Frame records (stored backwards from EOF)

Each frame record ends with a little-endian 16-bit total-size word. Frame deltas use XOR encoding against a 64,000-byte (320x200) chunky frame buffer:

  • Non-zero byte: XOR into current output position
  • Zero byte followed by N: skip N pixels
  • Zero byte followed by zero: end of frame

Captive DOS uses 16 ANM files for various animations (intro, game screens, cutscenes).

RNC — Rob Northen compression

Atari ST and Amiga resources may begin with RNC\x01 (Method 1) or RNC\x02 (Method 2).

RNC Method 1

  • 18-byte header: magic (4), unpacked size BE (4), packed size BE (4), unpacked CRC16 (2), packed CRC16 (2), unknown (2)
  • Three Huffman tables per sub-block
  • Forward decompression

RNC Method 2

Used in Liberation CD32 data. Old Amiga backwards stream:

  • 12-byte header
  • Reads compressed bytes from packed end, writes decoded bytes backwards
  • OpenCaptive verifies output byte-for-byte against separately decoded reference

ADF — Amiga disk image

Standard Amiga floppy disk format:

  • 80 tracks x 2 sides x 11 sectors x 512 bytes = 880 KiB
  • OFS (Old File System) or FFS (Fast File System)
  • Captive uses 1 ADF disk
  • Liberation uses 5 ADF disks (CaptiveII_Disk1 through CaptiveII_Disk4 + boot)

The adf_reader module reads the OFS filesystem structure. The amiga_ofs_inventory tool inventories content by SHA-256.

ISO9660 — Liberation CD32 disc image

Liberation CD32 comes as a raw BIN/CUE image:

  • Sector size: 2352 bytes (raw MODE1)
  • User data: 2048 bytes per sector, starting at offset 16
  • CDTV extensions present
  • Audio tracks: 10 tracks by Mark Knight (Track 02-11)

The iso9660_reader module validates directory records, extents and file sizes before returning buffers.

Atari ST disk image

FAT12 disk image. The BIOS parameter block begins at offset 11. Used for the Atari ST release of Captive.

x3g — Liberation 3D vector graphics

Liberation uses true 3D polygon rendering (not raycasting). Vector data is stored in .x3g files:

File pattern Content
{N}CityVectors.x3g City 3D geometry (4 variants, N=0-3)
{N}RoomVectors.x3g Room/interior 3D geometry
{N}BankVectors.x3g Bank interior vectors
{N}BarVectors.x3g Bar interior vectors
{N}ShopVectors.x3g Shop interior vectors
{N}Droids.x3g Droid 3D models
{N}CityMonsters.x3g City monster models
PoliceVectors.x3g Police/guard models
Monsters{2,3,4}.x3g Additional monster sets
People.x3g NPC models
Objects.x3g Item/object models

The internal binary format of x3g files is under analysis.

VGM — Liberation wall textures

Wall textures in Liberation use the .VGM format (referenced as WALL*.VGM). Internal structure is under analysis. Loaded via the wildcard pattern in the executable.

Img — Liberation graphics

Pre-rendered graphics in Liberation's Amiga image format:

File Content
MainSP.Img Main sprite sheet
MainSP16.Img 16-colour sprite sheet
3dView.Img 3D viewport frame/border
Taxi.Img Taxi graphics
backpack.img Inventory/backpack UI

AmSp — AMOS sprite bank

Used in Liberation CD32. AmSp signature followed by entry count.

Record structure: 10-byte header, then words x height x (depth + 1) x 2 bytes. The extra plane is a 1-bit transparency mask. High bit of width word indicates odd bytes-per-row (the loader doubles low 15 bits and subtracts one).

Records are word-aligned: odd total payload is followed by one padding byte.

FNT — Liberation fonts

Font data stored as {N}Liberation.FNT with 4 variants (N=0-3). Format under analysis.

spr — Liberation sprites

Game menu sprites stored as GameMenu.spr. Format under analysis.

IFF ANIM — Amiga animation

Liberation Amiga floppy version uses IFF ANIM (opt5 interleave). Contains FORM/ANIM chunks with:

  • PACK — compressed frame data (planar images)
  • PALL — 32-colour palette
  • SCPT — animation script bytecode

The verified player reads big-endian 16-bit record sizes from SCPT, advancing by full size, stopping at zero size.

MIDI — Captive music

Captive DOS uses standard MIDI files for music. Eight tracks identified by SHA-256. Supports AdLib, Roland MT-32, PC speaker and Sound Blaster output in the original (OpenCaptive uses a built-in 32-voice square-wave synthesizer with ADSR envelope).

8SVX — Amiga audio samples

IFF 8SVX format for audio samples. Contains VHDR (voice header), BODY (sample data). Used for Amiga sound effects. OpenCaptive's 8-channel mixer with channel stealing handles playback.

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