Document soundbank findings

docs/formats/banks.md

@@ -0,0 +1,65 @@
+# Soundbanks and in-memory sounds
+
+Most short sound effects (footsteps, foley, combat, weapons, objects, UI, grunts) are **not in the WADs**: they
+are WEMs stored inside Wwise soundbanks, either loose in `SFX\*.bnk` or embedded in the UE3 packages (`.upk`).
+The catalog and the editor only cover the WADs (`wad.md`), so none of these sounds are listed or editable yet.
+Survey of the installed game (buildid 3718300) on 2026-10-09, read-only.
+
+## Inventory
+
+| where | banks | unique in-memory WEMs | in the catalog |
+|-------|-------|-----------------------|----------------|
+| loose `SFX\*.bnk` (Batman/Catwoman footsteps, 32 surfaces each, + `TST_Prep_Media`) | 65 | 1,117 | 0 |
+| banks embedded in `.upk` packages (in 1,432 of the 2,650 packages) | 3,340 | 15,641 (~276 MB) | 0 |
+
+The two sets share 119 media IDs: about **15,800 unique sounds** in total. The WADs, by comparison, are fully
+covered: the BKPK tables in the packages reference 2,543 WAD entries, all of them in the catalog.
+
+Embedded WEMs by bank name prefix: `Speech` 7,872, `CHR` (character foley, combat, bosses) 3,896, `PSO` 781,
+`WPN` 664, `NPC` 475, `OBJ` 439, `SEQ` 265, `GUI` 208, `PSA` 203, `MTN` 196, `PX` 195, `DVC` 100, `GEN` 80,
+`PHY` 73, `AMB` 65, `SBJ` 50, others < 30. The `Speech_` banks (e.g. `Speech_EMOTE_Batman`, `..._GRUNT`) are
+probably efforts/grunts rather than dialogue (there are no per-language packages); not verified by listening.
+All WEMs seen are Vorbis (format tag 0xFFFF), the same codec as the WADs: the footsteps are mono (4 stereo),
+the embedded ones mono or stereo (~22 % stereo in a 2,533-WEM sample).
+
+## Names
+- The community hash list names none of these media IDs; only the bank names are known.
+- `CookedPCConsole\CookedBanks.txt` lists all 3,345 cooked bank names. Bank ID = FNV-1 32 of the lowercased
+  name (the same hash Wwise uses for every name). 3,338 of them are embedded in packages, 4 are loose `.bnk`
+  files (`Init`, `Global`, `Music`, `Music_PDLC`); `AMB_OW_A6`, `AMB_OW_C1`, `AMB_OW_E1`,
+  `Speech_EMOTE_Thug_Muffled_Stop` and `Speech_GFxUI_ArkhamCityStories` were found nowhere.
+- Loose footstep banks are named in their STID chunk (`CHR_BatmanFootsteps_Concrete_Media`, ...).
+
+## Bank layout (version 56, Wwise 2011.1)
+Chunks `BKHD` {u32 version 56, u32 bank id, ...}, `DIDX` N x {u32 media id, u32 offset, u32 size} (offsets
+relative to the `DATA` payload, WEMs 16-byte aligned), `DATA`, `HIRC`, `STID` {u32 type, u32 count,
+count x {u32 bank id, u8 len, name}}. `Init` (`50C63A23.bnk`) has `STMG`/`ENVS` instead of media.
+`701C1363.bnk` holds only `BKHD`.
+
+HIRC Sound object (type 2) payload: u32 object id, u32 plugin id (`0x00040001` = Vorbis), u32 stream type
+(0 = in memory, 1 = streamed, 2 = prefetch), u32 media id, u32 bank id of the media; for in-memory sources
+then u32 offset, u32 size, where offset = `DATA` payload position (from the start of the bank) + DIDX offset
+and size = DIDX size (checked on every in-memory source of the footstep banks and of `BmGame.upk`).
+A few sources use media of another bank. Every streamed media ID found is in a BKPK table, i.e. a WAD sound
+(`wad.md`).
+
+## Banks inside packages
+- The packages are fully LZO-compressed (package version 805, licensee 101). For the survey they were unpacked
+  with Gildor's `decompress.exe` (gildor.org; used from the user's old modding folder, not part of this
+  repository) and searched for `BKHD` (banks) and `BKPK` (WAD indexes). `UnrealX.upk` (512 bytes) is not a
+  readable package (wrong tag, probably encrypted).
+- Bank blobs in packages: 41,798 for 3,340 bank IDs. Many banks are copied into several packages (e.g.
+  `CHR_CatwomanFoleySuit` 31 times, `CHR_BatmanFoleyBelt` 26). 302 bank IDs occur as several blobs with
+  *different* media subsets (often one WEM each, several per package), so a bank's media set is the union
+  of all its blobs.
+- Largest: `CHR_RobinFoleyCape` 300 WEMs, `CHR_BatmanFoleyCape` 282, `CHR_Clayface` 263,
+  `CHR_NightwingFoley` 242, `CHR_CatwomanFoleySuit` 225, `CHR_MrFreeze` 176, `CHR_Combat` 166.
+
+## Consequences for editing (not implemented)
+- **Loose banks**: a replacement means rebuilding `DATA`/`DIDX` and the in-memory offsets/sizes in the HIRC
+  Sound objects of that bank (and in any other bank whose sources use its media). Whether the game accepts a
+  bank that changed size is untested.
+- **Embedded banks**: the package must be rewritten (decompress, patch every blob of the bank, recompress
+  LZO, fix the package's chunk table and export offsets/sizes). A sound must be replaced in **every** package
+  that carries a copy, otherwise the game may load the original from another package.
+- Either way: unverified in game so far; the same WEM rules apply (`wem.md`).