83 lines
4.4 KiB
Markdown
83 lines
4.4 KiB
Markdown
# WEM format accepted by Arkham City (Wwise 2011.1, Vorbis)
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Derived from the game's WEMs; `ackit verify` / `tests/test_realgame.py` rebuild them byte-for-byte from these rules
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alone (all 10816 ITA WEMs; in SFX only the 4 looping music tracks with loop points differ).
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## RIFF layout
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`RIFF` size `WAVE`, then `fmt ` (0x42 bytes), optional `cue `/`LIST` (37 files), `data`.
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Odd-sized `data` chunks are **not** padded.
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### `fmt ` (0x42)
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| off | type | value |
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|-----|------|-------|
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| 0x00 | u16 | 0xFFFF (Wwise Vorbis) |
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| 0x02 | u16 | channels (1,2,3,4,5,6 seen) |
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| 0x04 | u32 | sample rate |
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| 0x08 | u32 | avg bytes/s = `(data_len - seek_size) * rate // total_frames` |
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| 0x0C | u16,u16 | 0, 0 |
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| 0x10 | u16 | cbSize 0x30 |
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| 0x12 | u16 | valid bits (16 or 24 = source bit depth, informational) |
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| 0x14 | u32 | channel mask (mono 0x4, stereo 0x3, quad 0x33, 5.0 0x37, 5.1 0x3F) |
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| 0x18 | 42 B | AkVorbisInfo (below) |
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### AkVorbisInfo (fmt+0x18)
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| off | type | field | rule |
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|-----|------|-------|------|
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| 0x00 | u32 | dwTotalPCMFrames | sample count |
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| 0x04 | u32 | dwLoopStartPacketOffset | `2 + setup_len` (relative to end of seek table) |
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| 0x08 | u32 | dwLoopEndPacketOffset | `data_len - seek_size` |
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| 0x0C | u16 | uLoopBeginExtra | 0 |
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| 0x0E | u16 | uLoopEndExtra | = uLastGranuleExtra |
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| 0x10 | u32 | dwSeekTableSize | bytes (4 per entry) |
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| 0x14 | u32 | dwVorbisDataOffset | `seek_size + 2 + setup_len` |
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| 0x18 | u16 | uMaxPacketSize | max audio packet payload |
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| 0x1A | u16 | uLastGranuleExtra | `sum(packet samples) - total_frames` (< blocksize) |
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| 0x1C | u32 | dwDecodeAllocSize | see "decode alloc" — **must be right** (too small = NULL write crash) |
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| 0x20 | u32 | dwDecodeX64AllocSize | `alloc + 8*nbooks + 40 + 52*nfloors` (fit; unused by 32-bit game) |
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| 0x24 | u32 | uHashCodebook | **FNV-1 32** of the stripped setup bytes; codec-setup cache key |
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| 0x28 | u8,u8 | uBlockSizes | log2 short, log2 long |
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## `data` chunk
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```
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[seek table: N x {u16 granule delta, u16 byte delta}]
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[u16 setup_len][stripped setup packet]
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[u16 len][audio packet] ...
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```
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- Seek points: walk packets; point at the first packet whose *end* granule >= previous point + interval
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(8192 for SFX/speech; music uses 1024 or other per-sound values). Byte offsets are relative to the
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setup start (end of seek table).
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- No identification/comment headers (rebuilt from fmt).
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## Stripped setup ("external codebooks")
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Standard Vorbis setup with: no `\x05vorbis` header; codebook count (8b), then each codebook as a
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**10-bit ID** into the built-in library; no time-domain section; floor type field removed (always 1);
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residue type 2 bits; mapping type removed; mode window/transform type removed. See
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`ackit/wwvorbis.py:transcode_setup` (bidirectional).
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Codebook library: the game's table (runtime `0x0158E748`, 598 books) is byte-identical to ww2ogg's
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standard `packed_codebooks.bin` (`ackit/data/game_codebooks.bin`). **Wwise 2011.2.x uses the aoTuV 6.03
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library instead** — same IDs, different books — which is why files from the newer encoder decode to
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garbage/silence in this game.
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Stock libvorbis (1.3.7, in ffmpeg and in the libsndfile wheels ackit uses) setups map onto this library for all tested rates with 1/2/4/5
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channels, and for 6 channels up to 32 kHz (its 5.1 books at 44.1/48 kHz are newer than the game).
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At 24 kHz q>=5 needs a book not in the library. The encoder probes and picks a compatible quality.
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## Audio packets
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- Blocksizes differ (e.g. 256/2048): "modified" packets — packet-type bit and the long-window
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prev/next flags are removed (mode number stays first).
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- Equal blocksizes (512/512, 1024/1024): standard Vorbis packets (type bit kept).
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- 2-byte size header, no granule.
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## Decode alloc (dwDecodeAllocSize)
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`0x30 + parser allocations + 4*nbooks + 8`, every allocation rounded up to 4 bytes. Parser
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allocations (Tremor-lowmem derived, `ackit/allocsize.py`):
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- codebooks: `nbooks*0x3C` + per book: decode table (`used<2` or nodeb==4: `used*8+4`, else
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`align4((used*(leafw+1)-2)*nodeb)`) + for dec_type 2 the quantized values (`align4(quantvals)` or
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`align4(2*quantvals)`).
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- floors: `nfloors*0x24` + per floor `a4(parts) + a4(11*(maxclass+1)) + a4(2*(posts+2)) + a4(posts+2) + 2*a4(posts)`.
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- residues: `nres*0x1C` + per residue `a4(ncls) + 8*ncls`.
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- mappings: `nmaps*0x14` + `a4(2*coupling_steps)` + `a4(channels)` if submaps>1 + `a4(2*submaps)`.
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- modes: `a4(2*nmodes)`.
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Exact on all 24 setups the game ships; in-game test E10 used a new setup with computed values.
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