UnheardCity/docs/formats/wad.md

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

The other SFX\*.bnk files and the banks embedded in .upk packages hold their WEMs in memory (not in a WAD); see banks.md. The toolkit does not read or modify them yet.