# Arkham City WAD / BKPK container format

All values little-endian. Verified by byte-identical round trips of every shipped WAD
(INT/ITA/FRA/DEU/ESN LOC WADs and `SFX\17705D3E.wad`) and every BKPK pack.

## WWAD (`*.wad`)

| off  | type | meaning |
|------|------|---------|
| 0x00 | 4s   | `WWAD` |
| 0x04 | u32  | version `0x01020000` |
| 0x08 | u32  | entry count N |
| 0x0C | u32  | table offset (always `0x1C`) |
| 0x10 | u32  | table size (`12*N`) |
| 0x14 | u32  | data start (header area size; `0x8000` LOC, `0x1000` SFX) |
| 0x18 | u32  | data size (`file size - data start`) |
| 0x1C | N x {u32 hash, u32 size, u32 offset} | |

Rules:
- Table sorted by `hash` interpreted as **signed** int32. Payloads stored in table order.
- Each payload starts at the next **0x1000-aligned** offset after the previous one.
- `size` = payload length rounded up to **0x800**; padding is zero.
- File ends 0x1000-aligned; header area after the table is zero.
- `hash` = Wwise media/file ID (names: `hashlist.txt`, e.g. `CHR_RadioScanner`, `AMB_Steel_B3`, `Music`).

Payload kinds:
- **LOC WADs**: each entry is a group of WEMs, the variations of one line (ITA: 10816 WEMs in
  2464 entries; e.g. `CHR_RadioScanner` holds 91). Each WEM starts at the next 0x800 boundary after
  the previous one (zero padding); 3 entries pack two WEMs back to back. Addressed `HASH:i`.
- **SFX WAD**: 79 grouped ambience/effect entries (260 WEMs) plus 4 **stream packs** (below).

Where the game gets the inner offsets: the entry IDs appear next to `BKPK` headers inside the
LZO-compressed UE3 packages (e.g. `BmGame.upk`, `OW.upk`, `Church_B1_*.upk`). Those embedded BKPK
tables give each WEM's offset **and size**. ackit does not rewrite `.upk` files, so these WEMs are
replaced **in place, no larger than the original** (zero-filled to the original size), and the WAD
layout never changes. The user's earlier quickbms-reimport mod did the same and was loaded by the game.
Only the 4 SFX stream packs, whose BKPK index is a loose `.bnk`, can change size.

## BKPK stream packs (`SFX\<ID>.bnk` + SFX WAD entry `<ID>`)

`EDF036D6` (Music, 314 WEMs, incl. the intro/front-end music `393BC53A`), `E8F980BE` (Music_PDLC, 75),
`57572DAC` (Global, 1), `FCA4F778` (1). The `.bnk` file is an index + an embedded soundbank; the WEM
data lives in the SFX WAD entry with the same ID.

| off  | meaning |
|------|---------|
| 0x00 | `BKPK` |
| 0x04 | version `0x01020000` |
| 0x08 | pack id (== WAD entry hash) |
| 0x10 | media count N |
| 0x18 | table size `12*N` |
| 0x1C | table offset `0x48` |
| 0x20 | total stream size (== WAD entry size) |
| 0x2C | end of table (`0x48 + 12*N`) |
| 0x38 | embedded bank size |
| 0x3C | embedded bank offset (0x800 or 0x1000; a normal BKHD/HIRC/STID bank) |
| 0x48 | N x {u32 media id, u32 size, u32 offset in the WAD entry} |

Rules: table sorted by media id; each media starts at the next **0x800-aligned** offset; total =
end rounded up to 0x800. Padding is mostly zero (a few non-zero bytes in `EDF036D6`; the tool keeps
original bytes where nothing moved).

Replacing a pack media (`ackit` target `EDF036D6/393BC53A`) rewrites the pack table (`.bnk`), the
WAD entry payload, and the WAD table/offsets. Verified in-game (NOTES.md, E2).

## Regular soundbanks (`SFX\*.bnk`, bank version 56)

BKHD / DIDX {id, offset, size} / DATA / HIRC / STID. In-memory WEMs (DATA) are 16-byte aligned.
`ackit/bnk.py` can read/rebuild them, but most front-end sounds come from banks embedded in UE3
packages (`.upk`), which this toolkit does not modify.