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Bethesda Games — XeNTaX Forum Knowledge

Extracted from xentax forum dump (22 threads, 2010–2020). Organized by topic. Source threads cover TES3–5, FO3/NV/4/76, Oblivion, and Switch ports.

Cross-references to site reference docs:

1. BSA Archive Format (TES3–TES5, FO3/NV)​

Structure​

BSA archives are the primary container format for Elder Scrolls and early Fallout games. Each archive contains a header, file records, folder records, and file name strings.

Supported games (CynicRus, 2014):

  • TES3: Morrowind
  • TES4: Oblivion
  • TES5: Skyrim
  • Fallout 3
  • Fallout 3: New Vegas

BSA header format (Zero Diamond, 2010):

struct BSAHeader {
 uint32 magic; // "BSA\0"
 uint32 version; // 104 (Skyrim LE), 105 (Skyrim SE)
 uint32 offset; // Offset to filename buffer
};

Version notes:

  • v104: Skyrim LE, uses zlib compression
  • v105: Skyrim SE, uses LZ4 compression

Extraction tools:

  • BSArch (official Bethesda tool)
  • F4 Tools / BAE (Fallout 4 Archive Extractor)
  • Fallout Mod Manager (FOMM) — works for TES5 BSA extraction (JPulowski, 2011)
  • CynicRus BSAExtractor (Delphi, open source): https://github.com/CynicRus/BSAExtractor

Key observations​

  • BSA format changed between Morrowind and Oblivion (TaylorMouse, 2011: "They don't seem to be the same bsa files as Morrowind")
  • Game File Explorer can open BSA files and view IMG/### files with COL palettes (Zero Diamond, 2010)
  • BSA files can contain multiple data types: meshes, textures, animations, scripts, strings

2. BA2 Archive Format (Fallout 4 / Fallout 76)​

Overview​

Fallout 4 introduced the BA2 archive format (also referred to as "BTDX" from its magic bytes). Two distinct sub-formats exist:

  1. GNRL — General format (meshes, scripts, audio, etc.)
  2. DX10 — Texture format (DDS textures with DX10 headers)

BA2 GNRL Header (Ekey, 2015)​

idstring "BTDX" // Magic: "BTDX"
get VERSION long // Version number
idstring "GNRL" // Sub-format identifier
get FILES long // Number of files
get NAMES_TABLE_OFFSET long
get NULL long
// Followed by file entries and names table

File entry structure:

get DUMMY long // Unknown
getdstring EXT 4 // File extension (4 chars)
get DUMMY long // Unknown
get DUMMY long // Unknown
get OFFSET long // Offset in archive
get NULL long // Padding
get ZSIZE long // Compressed size
get SIZE long // Decompressed size
get DUMMY long // Unknown

Extraction logic:

if ZSIZE == SIZE:
 log NAME OFFSET ZSIZE # Uncompressed
else:
 clog NAME OFFSET ZSIZE SIZE # Compressed (zlib)

BA2 DX10 Texture Format​

Texture archives use DX10 DDS headers. The archive stores the DXGI format directly.

Key details (MrAdults, 2015):

  • Textures are stored with full DX10 DDS headers
  • DXGI format is relayed directly from the archive
  • BC5 (ATI2) is used for normal maps AND roughness/metalness (not just normals)
  • BC5 is also used for single-channel spec maps where both channels are identical (should be BC4)
  • Noesis v4.171+ supports FO4 archives/textures/NIFs

DDS header template (Loomy, 2016 — 010 Editor):

typedef struct {
 CHAR fType[4]; // "DDS "
 uint32 size; // 124
 ubyte flags[4];
 uint32 height;
 uint32 width;
 uint32 sizeorpitch;
 uint32 depth;
 uint32 mipmapcount;
 uint32 alphabitdepth;
 uint32 reserved[10];
} DDSHEADER;

typedef struct {
 uint32 size;
 ubyte flags[4];
 uint32 fourcc;
 uint32 rgbbitcount;
 uint32 rbitmask;
 uint32 gbitmask;
 uint32 bbitmask;
 uint32 alphabitmask;
} PIXELFORMAT;

Texture header fields (GRiNDERKILLER, 2016):

uint fileID
uint filetype
uint dxcomptype
ubyte zero
ubyte ? // Unknown
ubyte depth?
ubyte zero
ushort width // Can be byte-swapped
ushort height // Can be byte-swapped
ubyte mipscount
ubyte ?
ubyte ?
ubyte ?
uint startoffset
uint zero
uint compsize
uint pixscount
uint zero
uint ?
uint startoffset_mips
uint zero
uint compsize_mips
uint pixscount_mips
uint ?
uint ?

QuickBMS Extraction Script (Ekey, 2015)​

For GNRL archives:

# Fallout 4 (BA2 format) — GNRL
idstring "BTDX"
get VERSION long
idstring "GNRL"
get FILES long
get NAMES_TABLE_OFFSET long
get NULL long
savepos TEMP

goto NAMES_TABLE_OFFSET
for i = 0 < FILES
 get NSIZE short
 getdstring NAME NSIZE
 putarray 0 i NAME
next i

goto TEMP
for i = 0 < FILES
 get DUMMY long
 getdstring EXT 4
 get DUMMY long
 get DUMMY long
 get OFFSET long
 get NULL long
 get ZSIZE long
 get SIZE long
 get DUMMY long
 getarray NAME 0 i
 if ZSIZE == SIZE
 log NAME OFFSET ZSIZE
 else
 clog NAME OFFSET ZSIZE SIZE
 endif
next i

For texture archives, replace idstring "GNRL" with get MAGIC long (Ekey, 2015).

Fallout 76 BA2 Changes​

  • BA2 archives in FO76 still use the BTDX header (Notex, 2018)
  • Pre-launch files were encrypted (starting with -> magic) but retail files use standard BA2
  • BAE v0.9.0.15 handles FO76 archives correctly

Extraction Tools​

  • BAE (Bethesda Archive Extractor): https://www.nexusmods.com/fallout4/mods/78 — handles GNRL and DX10
  • F4 Tools (michalss, 2015): Extraction + GNRL repacking; textures supported from v3+
  • BSArch (official Bethesda): Handles all BA2 variants
  • Noesis (MrAdults, 2015): v4.171+ can extract archives + textures + load NIFs with auto-texture-loading

3. NIF Model Format (Skyrim / Fallout 4)​

Skyrim NIF Format​

Standard Gamebryo NIF format. NifTools/NifSkope supports it.

Key tools:

  • NifSkope (view/edit)
  • 3DS Max NIF importer/exporter (MajinCry, 2015)
  • Noesis (MrAdults, 2015)

Fallout 4 NIF Changes (MrAdults, 2015)​

Major changes from Skyrim NIF:

  1. BSTriShape — New shape type with embedded geometry (no data link to separate NiTriShapeData)
  2. Flattened skeleton — Many character models use a flattened hierarchy; reference skeleton.nif for proper hierarchy
  3. FP16 vertex positions — Bind pose centered at 0 for maximum FP16 precision
  4. New bone reference/inverse pose data — Minimal changes
  5. PBR material system — Core values and texture sets mostly same as Skyrim despite PBR addition

Noesis NIF loading commands:

-nifloadskel <filename> # Load external skeleton for hierarchy
-nifnotransform # Don't transform geometry (for exported pieces)
-ddsati2nonorm # Disable ATI2 normalization (safe for all FO4)
-fbxnewexport # Export current FBX format (not legacy 6100)

Vertex format flags (jonwd7, 2015):

  • 17 unique vertex flag combinations across all FO4 NIF files
  • Flags determine vertex buffer layout (position, normal, tangent, UV, vertex colors, skin weights)
  • Can be decoded via XOR between known buffer configurations
  • gpuBufferSize field must be correct or PS4/XB1 will break (MrAdults, 2016)

Bind pose technique (MrAdults, 2015):

  • FO4 uses traditional Gamebryo "EVERYTHING HAS A TRANSFORM" approach
  • Bind pose centered at 0 to maximize FP16 precision
  • Node space pose = bind pose after conversion
  • Recalculate on export: newInvBindPose * fittedPose where fittedPose quantizes to FP16

Texture path handling (throttlekitty, 2015):

  • Texture paths sometimes start with textures\\ and sometimes don't
  • Extract all texture archives to a common directory for auto-loading

Fallout 76 NIF Compatibility​

  • FO76 NIF files do NOT work with the FO4 Noesis script (silverm9, 2018)
  • Some imports only load the armature; others give "list index out of range"
  • NifSkope 2.0 Dev can open and export FO76 models as OBJ (qs12, 2020)

4. Texture Formats​

DDS / BCx Compression (Fallout 4)​

Block Compression formats (volfin, 2016):

  • BC1 (DXT1): 4:1 compression, 1-bit alpha
  • BC3 (DXT5): 4:1 compression, interpolated alpha
  • BC4 (ATI1): Single-channel (grayscale)
  • BC5 (ATI2): Dual-channel (normal maps, roughness/metalness)
  • BC6H: HDR
  • BC7: High-quality RGBA

Noesis ATI2 handling (MrAdults, 2015):

  • Noesis ATI2 = BC5
  • BC5 stores z derived + renormalization (correct for normal maps)
  • FO4 uses BC5 for roughness/metalness (no z derivation needed)
  • Use -ddsati2nonorm flag for all FO4 textures

Intel DDS Photoshop plugin: https://software.intel.com/en-us/articles/landing-page/01000-dds-plugins-reference-guide

Nintendo Switch Textures (Skyrim Switch)​

Switch texture format (Acewell, 2019):

  • Uses Nvidia Tegra X1 (XTX) format
  • Width at offset 0x40 (int)
  • Height at offset 0x44 (int)
  • Format ID at offset 0x50 (int):
  • 0x42 = DXT1 (BC1)
  • 0x44 = DXT5 (BC3)
  • Mipmap count at offset 0x54 (int)
  • Total data size at offset 0x58 (int)
  • Mip offset table starts at 0x5C
  • Image data starts at 0xD0

Tools:

Early Bethesda Image Formats (Arena / Terminator)​

File types (Zero Diamond, 2010):

  • COL: Palette files (256 entries, 3-byte RGB triplets, red in low byte)
  • CFA: RLE compressed + muxed animations (variable frames)
  • DFA: RLE compressed, partial animations following base frame
  • IMG: Three variants — no-header, uncompressed with header, compressed with unknown algorithm
  • SET: 64x64 blocks of IMG data
  • ###: Mixed image/animation container (Future Shock, SKYNet)

Source code reference: WinArena includes ParseBSA.cpp with full format documentation.

5. Audio Formats​

xWMA Format (Skyrim)​

  • xWMA is WMA frames in a RIFF container (Axsis, 2011)
  • Can be converted to PCM using xWMAEncode from X360 SDK
  • May be convertible to standard WMA without re-encoding (unconfirmed)

PS3 XWM/MSFC Format (Skyrim PS3)​

  • Header tag: MSFC (NotDukeNukem, 2012)
  • Not the same as standard MSF format
  • Conversion script: msf2at3 by AlphaTwentyThree (works with Atrac codec)
  • Install Atrac codec for audio editor support

6. Save File Formats (Oblivion)​

References (jonwil, 2015):

7. EGM Morph Format (Oblivion)​

EGM format (falconcool, 2010):

  • Controls face morph data for facial expressions (speaking, blinking, etc.)
  • Each vertex in the head mesh has an index number
  • 010 Editor script exists for modifying vertex data: http://www.tesnexus.com/downloads/file.php?id=18566
  • Limitation: Cannot add new vertices, only modify existing ones
  • Adding new head meshes requires new morph data for all facial expressions

8. Cell/Landscape Data​

CellToNif Conversion​

Tool: CellToNif by Yacoby — converts Morrowind cell mesh data to 3D NIF format

Cell grid sizes:

  • Morrowind: 64x64 cell grid
  • FO3/NV, Oblivion, Skyrim, FO4: 32x32 cell grid

VHGT data (ReeceMix, 2017):

  • Height data stored as signed bytes (e.g., 7F 81 = height value)
  • 1024 DWORDs expected for a 32x32 cell (but实际 may be fewer)
  • Landscape is heightmap-based across all Bethsoft games
  • Game-to-game cell data is NOT natively compatible (offsets differ)

Documentation sources:

9. Cross-Engine Porting​

Bioware → Bethesda (B2B Project)​

Project: https://github.com/dhk-room101/B2B (adludum, 2018)

  • Automatic porting of Dragon Age Origins content (quests, dialogues) to Skyrim engine
  • Based on Figment/Snip for Bethesda side
  • Bioware side inspired by Rick (@gibbed) Dragon Age work
  • Same process can port KoTOR to Fallout 4

10. Tool Reference​

ToolPurposeGamesAuthor/Source
Noesis v4.171+Archive extraction, NIF/texture viewing, FBX exportFO4, FO76MrAdults
NifSkope 2.0 DevNIF viewing/editing, OBJ exportFO4, FO76jonwd7
BAEBA2 extractionFO4, FO76Nexus Mods
F4 ToolsBA2 extraction + GNRL repackingFO4michalss
BSArchOfficial archive toolTES5, FO4Bethesda
BSExtractorBSA extraction (Delphi)TES3–5, FO3/NVCynicRus
FOMMBSA extractionTES5SourceForge
CellToNifCell mesh → NIFMorrowindYacoby
TESAnnwynHeightmap importTES3–5, FO3/NV—
XTX-ExtractorSwitch texture extractionSkyrim Switchaboood40091
RawTexSwitch texture viewingSkyrim Switch—
Intel DDS PluginBCx texture support in PhotoshopFO4Intel
hkxcmdHKX ↔ XMLTES5, FO4figment
havok2fbxHKX → FBXFO4Highflex

11. Key Discoveries & Gotchas​

  1. BA2 texture archives need different extraction — GNRL script doesn't work for DX10; change idstring "GNRL" to get MAGIC long
  2. FO4 NIF bind pose is centered at 0 — not a bug, intentional FP16 optimization
  3. BC5 used for non-normal data — FO4 uses BC5 for roughness/metalness, not just normals
  4. Texture paths are inconsistent — some start with textures\\, some don't
  5. FO76 NIFs are incompatible — FO4 Noesis script fails on FO76 models
  6. Switch textures use XTX format — not standard DDS; need XTX-Extractor or RawTex
  7. Bodyslide-generated NIFs may break — gpuBufferSize can be incorrect, breaks console rendering
  8. Cell data is not cross-game compatible — Bethesda alters format between games despite same method
  9. BSA versions differ — v104 (zlib) vs v105 (LZ4) between Skyrim LE and SE
  10. 17 unique vertex flag formats in FO4 NIFs — must handle all for correct mesh loading

Sources​

  • Zero Diamond (2010): Bethesda file formats (COL/CFA/DFA/IMG/SET)
  • Ekey (2014–2015): FAT/DAT headers, BA2 extraction scripts
  • MrAdults (2015): Noesis FO4 support, NIF format analysis, BC5 handling
  • jonwd7 (2015): Vertex flag analysis, NIF format debate
  • michalss (2015): F4 Tools, BA2 extraction
  • Loomy (2016): DDS header template (010 Editor)
  • GRiNDERKILLER (2016): Texture header field layout
  • Acewell (2019): Switch texture format specs
  • shakotay2 (2016–2018): NIF debugging, hex2obj
  • throttlekitty (2015): Texture pathing, FBX version
  • volfin (2016): BCx format references, Intel plugin
  • adludum (2018): B2B cross-engine porting project