Sylpheed/docs/re/structures/slb-data-offset.md

✅✅ SUPERSEDED IN ITS CAUSE (2026-08-26) — see branch auto/slb-loader. The four offsets are not a header size. They are a packing phase:

X = (cumulative start of the .pNN segment holding the bank) mod 2048

segment	size	cumulative start	start mod 2048
sound.p00	267 930 992	0	0
sound.p01	268 404 812	267 930 992	1392
sound.p02	268 404 868	536 335 804	1468
sound.p03	268 384 384	804 740 672	1600
sound.p04	14 903 296	1 073 125 056	1728

Independently reproduced here: the four values I measured are exactly the running sums of the five segment file sizes, mod 2048. The XMA grid is 2048-aligned inside each .pNN file; the segments are not multiples of 2048 long; so every join shifts the phase, and the flat concatenation the TOC addresses inherits the shift.

Two things I wrote on this page are therefore wrong in their explanation, even though the measurements stand:

• "It varies by language and subdirectory" — that was a correlation, not a cause. Directories cluster into segments, so the per-directory table is real but explains nothing.
• "The header is high-entropy content of a size the loader must know a priori" — there is no header. Those bytes are the previous bank's audio, which is why they looked like data and had no length field: they are data.

The heuristics below (99.62 % packet scan, 99.97 % seek residue, 99.95 % combined) are all superseded by an exact rule, verified 8 783/8 783 on the other branch. slb.rs still uses the heuristics; the exact fix needs PakArchive to expose the segment phase, which is an API change.

.slb leading-stream data offset — 1392 was never a constant

✅ Settled 2026-08-26, verified by decoding. A bank's leading headerless packet stream does not start at a fixed offset. It starts at first_riff % 2048. HEADERLESS_DATA_OFFSET = 1392 is the value that offset happens to take in <lang>\etc\, and assuming it everywhere starts the decode mid-packet and throws away almost all of the audio.

Read this first — the settled state of the .slb container

This page grew as a chronological record, and several of its sections are superseded readings kept for their reasoning. Everything below the summary is history; this table is what is currently true.

question	answer	confidence
where a bank's headerless stream starts	first_riff % 2048, or scan_data_offset when there is no RIFF	✅
why that takes four values (1392/1468/1600/1728)	it is a packing phase: (cumulative .pNN segment start) mod 2048. Not a header.	✅
what the bytes before it are	the previous bank's audio	✅
where a wave ends	data_at + declared_size, confirmed by seek magic there — 7 620/7 620	✅
are the declared data sizes honest	yes. The TOC window is not the wave boundary.	✅
a wave's length in seconds	data_bytes / PsuedoBytesPerSec. Not the seek table's sample total, which understates by a median 9.7 %.	✅
channel count	the byte at RIFF + 49. 2.12 % are stereo; forcing mono yields one frame.	✅
seek chunk layout	+4 size LE (8 + 4·packets), +8 stream count, +12 packet count LE, +16 cumulative sample table	✅
which wave an entry names	the first wave starting at/after its offset, or the second when a leading wave + 12 288-byte block precedes — 7 620/7 620	✅
the 12 288-byte block	seek chunk + a cue-shaped record + sparse zeros; its first two words are table[-2], table[-1]	✅ / 🟡
what the block's id field refers to	a real cue, but not this entry's and not a chain	❔
headerless bank durations	unrecoverable — no seek table to read, and the first seek in the entry usually belongs to the previous bank	❔

Enumerating every wave without the TOC: scan the flat stream for seek, keep chunks where size == 8 + 4·count and seek_pos − count·2048 ≥ 0. That yields 9 661 waves with zero false positives across 1.01 GB.

Four mistakes of mine are recorded below rather than deleted, because each one's reasoning is the useful part: reading the packet count big-endian; believing a one-frame decode meant missing audio (it meant stereo); using the seek table's sample total as a duration; and refuting the leading-segment hypothesis with a predicate that was wrong by a constant I had not yet found.

---

The rule

XMA1 packets are 2048 bytes and the leading stream is a whole number of them ending at the first RIFF. So its start is forced:

start = first_riff % 2048

Disc-wide that lands on exactly four values — 1392, 1468, 1600, 1728 — all of the form 1392 + 4k. Across the 3 965 Japanese and 3 393 English banks with a non-empty leading region, no other value occurs:

	1392	1468	1600	1728
eng\etc, eng\Movie, eng\Briefing	1 520	—	—	—
eng\Voice	8	1 873	—	—
jpn\etc	—	1 402	303	—
jpn\Briefing	—	71	—	—
jpn\Movie	—	—	61	—
jpn\Voice	—	—	2 033	95

It varies by language and subdirectory, which is why a constant derived from eng\etc\ looked right for years' worth of the banks anyone had reason to open.

Verified by decoding, not by arithmetic

The alignment argument alone proves nothing — any offset can be made to "align" by definition. The test is whether more audio comes out. Decoded through FFmpeg's xma1 at mono/48 kHz, on a random sample of 140 banks that have a non-empty leading region:

outcome	banks
more audio at ri % 2048	85
byte-identical	54
less audio	1

Median gain among the improved: 70×. The 54 identical ones are the control — they are the eng\etc-style banks where ri % 2048 is 1392, so the rule must and does reproduce the old behaviour exactly. Individual cases:

eng\Voice\VOICE_TCAF_592.slb    1 506 ->  97 152 bytes   (65x)
jpn\Voice\VOICE_TCAF_592.slb    2 910 -> 127 178 bytes   (44x)
eng\etc\VOICE_D_452.slb        30 154 ->  30 154 bytes   (unchanged, control)

The one counterexample — ✅ explained

eng\Voice\VOICE_TCAF_608.slb decodes 2 840 bytes at 1392 and 896 at 1468.

It is not a bank where the old constant works and the derived offset fails: both offsets yield well under a tenth of a second from a 38 988-byte region, i.e. both fail, and 1392 merely produces marginally more garbage.

The reason is that the bank is truncated. Its data chunk declares 759 808 bytes and the pak entry holds 8 864 — 99 % short. There is almost nothing there to decode at any offset. See the section below.

❌ This withdraws my own claim from earlier the same day

sound-pak-contents.md reported that the leading region rule holds for "0 of 5 100 Japanese banks" and filed a backlog item saying the Japanese banks were a different, undecoded layout. That was wrong. The Japanese banks are the same format; only the offset differs. The measurement behind it was correct — zero of them satisfy (riff − 1392) % 2048 == 0 — but the conclusion drawn from it was not, and the reason is instructive: I treated HEADERLESS_DATA_OFFSET as a property of the format when it was a property of the sample the format was derived from.

The same error was hiding a defect in the English set too: 1 873 eng\Voice banks sit at 1468 and were being decoded mid-packet just as badly.

The RIFF-less banks had the same bug, plus a worse one

✅ Settled 2026-08-26. 1 495 banks (799 jpn, 696 eng) carry no RIFF at all and take a separate code path. That path was wrong twice over:

1. it used the constant offset, with no RIFF to derive from; and
2. it built a stereo fmt chunk.

Decoded across a random 48-bank sample:

banks where the old stereo-at-1392 beat the best mono offset	0 of 48
median gain	184×
range	25× – 489 344×

Stereo is the same failure signature recorded for the leading segment: it stops after one frame. Individual banks went from 0–4 816 bytes to 180 000–380 000.

The winning offsets fall out by directory, and they reproduce the distribution measured independently from the RIFF-bearing banks — which is the cross-check that makes this more than curve-fitting:

eng\etc 1392 (11/11)   eng\Voice 1468 (9/9)   eng\Briefing 1392 (2/2)
jpn\Voice 1600 (12/13) jpn\etc 1468 (8/12), 1600 (4)

Note jpn\etc splits, so the path alone is not enough to pick the offset.

Picking the offset without a decoder

An XMA1 packet opens with a big-endian header — 6 bits frame count, 15 bits frame-offset-in-bits, 3 bits metadata, 8 bits packet-skip. At the true offset those fields stay in range packet after packet; one byte off and they do not. Scoring the first 24 packets and taking the best candidate:

7 330 of 7 358 (99.62 %) on the labelled set — every bank that has a RIFF, where the answer is forced and therefore known. All 28 misses are ties on the top score; there is not a single case where the scan picks wrongly with a unique winner. scan_data_offset therefore falls back to 1392 on a tie.

This is used only for the RIFF-less banks. Where a RIFF exists the offset is derived from it exactly, never scanned.

✅ A second, independent signal — and it breaks the ties

Settled 2026-08-26. The 28 ties needed a different signal, not more of the same one, and the banks carry one: a seek chunk sitting on a packet boundary. Its position modulo 2048 therefore is the data offset.

seek at 3 516 / 5 564 / 7 612 / 9 660 / 13 756 / 19 900  —  all ≡ 1468 (mod 2048)

On the 6 033 labelled banks that have a seek before their first RIFF, 6 031 agree (99.97 %) and 2 disagree. That is better than the packet scan and, more importantly, structural rather than statistical — which is why it is now tried first.

Applied to the packet scan's 28 ties: 26 resolved correctly, 0 wrongly, and 2 with no usable seek. The combined rule — seek residue, else packet plausibility, else 1392 — scores 7 354 / 7 358 = 99.95 % on the labelled set, up from 99.62 %.

762 of the 1 495 RIFF-less banks carry a seek, and its residue lands on the four known offsets there too (1468 ×343, 1600 ×255, 1392 ×148, 1728 ×16), so the signal is available in the population that needs it.

❌ The header is not audio being discarded

Worth ruling out, since a wrong data offset was the whole subject of this page: if the bytes before the offset were audio, we would be throwing away the start of every clip. Adding 0 to the candidate set and re-running the scan, it wins 6 of 7 358 — noise. The header is genuinely not part of the packet stream. (1 482 banks have an all-zero header; 5 876 have content in it, which is what prompted the check.)

Is that 99.62 % transferable? — checked, and it is conservative

The labelled set has a RIFF; the population the scan actually serves does not. Since the scan is unbounded it reads past the RIFF on labelled banks, so the 99.62 % could have been borrowing discriminating power that a RIFF-less bank cannot offer. That would make the headline number optimistic for the only case it is used in — worth checking before trusting it.

Confining the scan to the leading region drops it to 69.98 % with 1 910 ties, which at first looks like exactly that problem. It is not. Splitting by how much leading audio there is separates the two explanations:

	correct	ties
unbounded, all 7 358 labelled banks	99.62 %	28
confined to the leading region, all 7 358	69.98 %	1 910
≥24 packets of leading audio (989 banks), unbounded	100 %	0
≥24 packets of leading audio (989 banks), confined	100 %	0

The last two rows settle it. Where there is enough audio to score, the discriminator is perfect whether or not the RIFF is in range — so it is not leaning on the RIFF. The 69.98 % is an artifact of short leading regions: with only two or three packets to judge, candidates tie and the tie-break decides. Unboundedness helps those banks by giving the scan more bytes, which is why the two columns differ at all.

A RIFF-less bank is a whole pak entry, tens of kilobytes, so 24 packets are always available — it is always in the 100 % regime. The 99.62 % figure is therefore conservative for the population the scan is used on, not optimistic.

What this does not settle

• ❔ Why the offset takes those four values, and what the bytes before it are. This was probed and remains open; what is now ruled out is recorded below.

• The 28 ties. The scan cannot separate them and falls back to 1392, which is right for roughly a third of that population and wrong for the rest.

• Why the offset takes exactly these four values by directory is still unexplained — see above.

• Nothing here was run in the game — this is a decoder-side result measured with FFmpeg as the oracle.

🟡 Most banks declare more data than they store

Measured 2026-08-26. Of the 7 586 banks that carry both a RIFF and a data chunk after it, 5 296 (69.8 %) declare a data size larger than the bytes actually present in the pak entry. The remaining 2 290 declare less, which is the ordinary multi-sub-wave case. Not one declares exactly what it holds.

Worst cases run to 99 % short:

eng\Movie\VOICE_RT16C.slb    declared 1 810 432   available 489 392   -73 %
jpn\etc\VOICE_D_589.slb      declared 1 177 600   available   6 708   -99 %
eng\Voice\VOICE_TCAF_608.slb declared   759 808   available   8 864   -99 %

This contradicts a claim in the decoder's own comment, which says the declared size "is honest per sub-wave". It is not, for about seven banks in ten. The code is nonetheless safe — it clamps the range with .min(slb.len()) — so this is a documentation defect and an integrity observation, not a crash.

⚠️ Method note on this measurement. My first pass searched for data from offset 0, which can hit those four bytes by chance inside the leading audio region and read a garbage length. Re-running it anchored after the first RIFF changed the count from 5 038 to 5 296 — the flaw was slightly under-counting, but it could as easily have gone the other way, and an unanchored chunk search over binary audio is not a safe way to ask this question.

❔ Why the declared sizes are too large is not settled. Plausible readings — an authoring-time allocation that was never trimmed, or deliberate truncation of unused tails — are guesses; nothing here distinguishes them, and the game has not been observed reading one of these banks.

❔ What the header is — four things it is not

The bytes before the data offset are still unexplained, but the field has been narrowed. Probing the header of banks at each of the four offsets:

• Not a length field. There is no word in the first 64 bytes equal to the offset, the offset minus 1392, the RIFF position or the entry size, in either endianness. The offset has to be derived; it is not read.
• Not a seek table or any ascending index. Treated as big-endian words, only about half of consecutive pairs are non-decreasing — which is what random data gives. Every word is distinct and none is zero, across all four offsets.
• Not zero padding, at least not usually: 1 482 of 7 358 banks have an all-zero header, but 5 876 have content in it.
• Not audio being discarded. Adding 0 to the offset candidates, it wins 6 of 7 358 — noise. (Recorded above.)

So it is high-entropy content of a size that is constant per language and subdirectory, carrying no field that names its own length. That combination suggests something the loader knows the size of a priori rather than something self-describing.

First step if this is picked up again: find the loader. SETTINGS.PATH is game:\dat\sound.pak+ and SETTINGS.PARAM is Pj_Silph.xgs, so there is code that opens a bank by name and seeks to its data; the constant, or the table it indexes, should be visible there. That is static PE work (/work/*.pe, offset = VA − 0x82000000), not another pass over the archive — this page has taken the byte-level evidence about as far as it goes.

⚠️ Disagreement on the declared-data question — not resolved

auto/slb-loader withdraws the 🟡 finding above that 69.8 % of banks declare more data than they store, reporting instead that declared sizes are exact (260/260 checked) and that the extra bytes live outside the TOC window but still in the .pNN stream — and specifically that VOICE_TCAF_608 is not truncated.

I could not reproduce that, and the arithmetic is against it. Walking that bank's chunks gives a clean, internally consistent structure:

window = [662 403 072, 662 456 412)   size 53 340
RIFF at +40 380, its size field 761 360
  fmt   32
  Dmmy  4 028
  data  759 808          <-- declared

The next TOC entry begins at 662 458 368, i.e. 55 296 bytes after this one starts. 759 808 bytes of audio cannot fit there. They would have to span roughly fourteen further TOC windows.

Both readings agree on the underlying fact — the declared size exceeds the TOC window — and differ on what follows from it. Mine said "truncated", which was an over-claim I withdraw: the 1 928 non-zero bytes in the 1 956-byte gap after the window, and the audio-looking bytes at the next entry, are consistent with a bank's data simply continuing past its window. But "declared sizes are exact" requires a wave to span many named entries, which is a much stronger claim than "the bytes are outside the window".

✅ The experiment was run — the data does not span windows

Read VOICE_TCAF_608's declared 759 808 bytes straight out of the flat stream, ignoring the window boundary, and decoded through FFmpeg's xma1:

read	bytes in	decoded
data → window end	8 864	896 bytes = 0.01 s
data → full declared size	759 808	896 bytes = 0.01 s
control VOICE_D_452, declared fits	26 624	208 970 bytes = 2.18 s

Reading 86× more bytes yields not one extra sample. The bytes past the window are not this bank's audio, so "the bytes are outside the TOC window but still in the .pNN stream" does not hold here — and this is the very bank the other branch named as not truncated. (No segment join is crossed: the read sits inside sound.p02, so the packing phase is not a confound.)

So for VOICE_TCAF_608 the audio really is not present. I still withdraw the word "truncated" as an over-claim about the other 5 295 banks — I measured that their declared size exceeds their window, not what is in the bytes beyond it, and I have now tested exactly one of them. What is established is narrower and worth stating exactly:

• ✅ the declared data size exceeds the TOC window for 5 296 of 7 586 banks;
• ✅ for VOICE_TCAF_608 the missing bytes cannot be recovered from the stream;
• ❔ whether that generalises is untested — the same decode would have to be run across the population, which is the obvious next step and was not done.

❌ Decoded length is not a valid test of where a bank ends — my own test withdrawn

I set out to generalise the VOICE_TCAF_608 result across the 5 296 over-declaring banks, and the first pass looked like a clean reversal: on a random 60, reading the full declared size instead of stopping at the TOC window gained audio in 59, median 2.10×, up to 59×. That reads as "the data really does continue past the window", i.e. the other branch is right and my truncation reading was wrong.

Then I checked whether the declared size is an honest boundary at all, by reading twice it. If the stream ends where the header says, doubling the input should add little:

reading 2× the declared size yields >1.5× the audio	33 of 40
ratio of decoded bytes, 2× input vs 1×	median 1.64, p90 1.75

It keeps producing audio indefinitely. XMA1 packets are self-contained, so feeding the decoder the next bank's packets yields perfectly good audio that simply is not this bank's. The decoder cannot tell the difference, and neither can a byte count.

So the 59-of-60 result is withdrawn as evidence. It does not show that the declared size is honest; it shows only that something decodes after the window, which was never in doubt — the bytes there are audio, just possibly someone else's. This is the same error in a new costume as the unanchored data search earlier on this page: a measurement that returns a plausible number for a question it cannot actually answer.

What survives:

• ✅ VOICE_TCAF_608 is still special, and now more clearly so: for it, reading 86× more bytes gained nothing, where the typical over-declaring bank keeps yielding audio without limit. Whatever is at its offset does not decode at all.
• ❔ Whether the declared sizes are honest is unresolved by this method and cannot be resolved by it. A valid test has to identify the bank boundary independently of the decoder — the seek-chunk packet-count chain used on auto/slb-loader is exactly such a signal, and is the right next step.
• ❌ Both my "69.8 % are truncated" and my attempted reversal of it are off the table. The measured fact is unchanged and narrow: the declared data size exceeds the TOC window for 5 296 of 7 586 banks.

❔ The seek chunk's layout — identified, but it does not yield a packet count

The decoder-independent boundary signal this page called for is the seek chunk. Its shape is now readable; its arithmetic is not.

Immediately after the seek tag sits a little-endian size, then a short header, then a strictly ascending table:

eng\etc\VOICE_D_452     seek at +3 440   size 64    -> 16 words
eng\Voice\VOICE_TCAF_592 seek at +9 660   size 108   -> 27 words
eng\Voice\VOICE_TCAF_608 seek at +28 092  size 348   -> 87 words

words after seek+8 (big-endian):
  0x01000000, <varies>, 0, then ascending: 0, 1572864, 3932160, 6160384, ...

Word 0 is 0x01000000 in every bank examined — a version or entry-size marker. Word 1 varies and its top byte is 14 / 25 / 85 for the three above. Word 2 is 0, and the ascending run begins after it.

Two readings tried, both fail:

reading	D_452	TCAF_592	TCAF_608
declared data size ÷ 2048 (packets)	13	17	371
seek size ÷ 4 (entries)	16	27	87
entries − 3 header words	13 ✅	24 ✗	84 ✗

The third row is the near-miss that would be easy to adopt: it is exactly right for VOICE_D_452 and wrong for the other two. That is a one-of-three fit, and this page has already recorded two measurements today that returned plausible numbers for questions they could not answer — so it is recorded as failed, not as a rule with exceptions.

The ascending values are not packet indices: the steps (≈1.5–2.2 million) are far too large for a bank of a few hundred packets, so they are sample or fixed-point offsets on some other scale that has not been identified.

What the next attempt should know: the chunk is real, its size field is little-endian, three header words precede the table, and the entry count is not the packet count. auto/slb-loader reports chaining seek packet counts successfully across consecutive entries — whatever field it used is not one of the two tried here, and reconciling the two readings is the cheapest way in.

❌❌ VOICE_TCAF_608 is NOT truncated — I was decoding it as mono

2026-08-26, resolving the disagreement above in the other branch's favour. Everything I concluded about this bank was an artefact of a wrong fmt chunk, and the declared sizes are honest after all.

The seek chunk, read correctly. I read the packet count big-endian. It is little-endian, and the layout is:

+0   'seek'
+4   u32 LE  chunk size  (always 8 + 4*packets)
+8   u32 LE  stream count (always 1)   <-- my "0x01000000" was LE 1 here
+12  u32 LE  PACKET COUNT              <-- my "<varies>" read big-endian
+16  packets x u32 LE  cumulative decoded sample totals

Verified: size == 8 + 4*count on every bank checked. My "entries − 3" reading matched VOICE_D_452 by coincidence; the real relation is size/4 − 2.

And a seek sits immediately after its own data, so the first seek in an entry usually belongs to the previous bank — its implied start is negative (−25 232 for D_452, −145 988 for TCAF_608). I was comparing an entry's first seek against its first data, which are different waves by construction. That is why no reading could line up.

The declared sizes are honest — 7 620 / 7 620. For every RIFF-bearing entry on the disc there is seek magic at exactly data_at + declared_size, and its packet count × 2048 equals the declared size. Zero failures. For TCAF_608: probe at 663 207 356 → seek, count 371, 371 × 2048 = 759 808 = declared.

Why it decoded to 896 bytes: its Channels is 2. I decoded it as mono. Reading it as stereo gives 6 520 176 bytes = 33.96 s — and two independent length signals in the bank agree: the last cumulative sample 1 626 112 / 48 000 = 33.88 s, and 759 808 / PsuedoBytesPerSec = 33.97 s. The audio was there the whole time.

170 of 8 021 banks (2.12 %) are stereo — Channels is the byte at RIFF + 49. That is exactly the 1-in-60 rate of my "gains nothing" outlier.

What this retracts

• ❌ "VOICE_TCAF_608's missing bytes cannot be recovered from the stream" — wrong, nothing was missing.
• ❌ "The declared data size exceeds the TOC window for 5 296 banks" stands as a fact about the window, but my framing of it as a problem is withdrawn: the window is simply not the wave boundary, and data_at + declared_size is.
• ❌ My seek-layout write-up above (entry count, "failed readings") was wrong in its endianness and in its pairing assumption. Left in place as a record.

This is the mono/stereo trap already documented on this page — "at two channels every bank yields exactly 1792 bytes, one frame" — met from the other direction. Having written that down, I then spent several passes attributing a one-frame decode to missing data instead of checking the channel count.

Code fixed

to_xma_riffs built the leading segment with a hard-wired mono fmt . It now reads Channels from the bank's own first RIFF (riff_channels), falling back to mono only when there is no RIFF to read. 7 disc tests pass.

The decoder-independent boundary, for the record

bytes    = u32 LE at seek+12  x 2048   (== the `data` chunk size)
validate = 'seek' magic at data_at + declared_size          (7 620/7 620)
samples  = the LAST u32 LE entry in the seek table
channels = byte at RIFF + 49            <-- read it, never assume

🟡 Enumerating every wave on the disc, and a bank→wave assignment rule

2026-08-26. auto/slb-loader leaves open "which bank in a window belongs to the entry's name". This is a measured attempt at it, short of settled.

Every wave can be enumerated without reference to the TOC. Scanning the 1.01 GB flat stream for seek and keeping only chunks satisfying size == 8 + 4·count with a non-negative implied start gives 9 661 waves and rejects nothing — not one false positive in a gigabyte of audio. The identity is that strong. Each wave's extent is then [seek_pos − count·2048, seek_pos).

The assignment rule. Take an entry to name the first wave starting at or after its offset. Against the 7 620 entries where the answer is independently known (they carry a RIFF, so the wave is data_at for declared_size):

correct   7 338 / 7 620 = 96.30 %
otherwise   282

The 282 are one class, not a scatter. In every one, the first wave ends earlier than the RIFF, and the gap between that wave's seek and the first RIFF is exactly 12 288 bytes — the same value in all 282. A constant that sharp is structural, not noise. 12 288 is 6 packets, and also 3 × the 4 096-byte RIFF+Dmmy block the other branch identified.

I first guessed these were leading segments, which would put the earlier wave's seek at the first RIFF. That is refuted: it happens 0 times out of 282. Whatever occupies those 12 288 bytes is something else.

✅ The 12 288-byte region is a padded metadata block — and the rule is 100 %

I dumped it, as the previous paragraph said to. Across all 282:

• the region from the earlier wave's seek to the first RIFF is exactly 12 288 bytes — the same in every one;
• it opens with that wave's seek chunk (240–260 bytes);
• the tail after the chunk carries 47–57 non-zero bytes (median 52) and is otherwise zero padding, filling the block out to 12 288.

So an entry may hold a leading wave, then a 12 288-byte padded block, then its RIFF wave. With that, the assignment rule completes:

the entry's wave is the first wave at/after its offset	7 338 (96.30 %)
the second — a leading wave + 12 288 block precedes it	282
neither	0
first-or-second	7 620 / 7 620 = 100.00 %

❌ And this overturns my own refutation from one iteration ago. I proposed the earlier waves were leading segments, tested it as "the earlier wave's seek should sit at the first RIFF", got 0 of 282, and recorded the hypothesis as refuted. The hypothesis was right; my test was wrong by exactly the padded block — the seek sits at RIFF − 12 288, not at RIFF. A negative result is only as good as the predicate it tests, and mine was too strict by a constant I had not yet discovered.

⚠️ Consequence for the open duration question: the rule is now exceptionless on the checkable set, which is much stronger than the 96.30 % it replaced. It still cannot be verified on headerless entries — there is no RIFF there to check against — but "100 % wherever it can be checked, with a named structural reason for every case" is a materially better basis than before. The trailer's first two words are now identified — see below.

✅🟡 Inside the 12 288-byte block's trailer

2026-08-26. The block is seek chunk, then a trailer of 47–57 non-zero bytes, then zeros. Two of those bytes-groups are now named.

The trailer opens with two little-endian u32 words, and across all 282:

• ✅ w1 is the leading wave's total sample count — 282 / 282, exact. It is the same number as the last entry of that wave's own seek table, so the block restates the wave's length in a directly readable field.
• ✅ w0 < w1 in every case, and w1 − w0 is always a whole multiple of 512 — 282 / 282. 512 samples is the XMA1 frame, so the difference is a whole number of frames: 9 to 91, median 14.

Examples:

packets  w0        w1        leading wave's samples
63       409 600   445 440   445 440
61       375 808   410 624   410 624
12        68 608    75 264    75 264

🟡 What w0 means is not settled. A value that trails the total by a whole number of frames is the shape of a usable-length or loop-end field — decoder priming and the final partial frame are both counted in frames — but that is a reading of the shape, not a measurement, and nothing here distinguishes the candidates. It is recorded as 🟡 for that reason.

❔ The remaining ~48 non-zero bytes are scattered thinly across the 12 KiB rather than clustered — roughly 17 per KiB in blocks 1, 3 and 7, the rest empty. That is the shape of a sparse table, and it is unidentified.

A correction to how I described this block: I called the region "zero padding" after the seek chunk. It is not padding — it is a sparse structure that is mostly zero. The distinction matters for anyone who tries to skip it.

❌ The seek table's sample total is NOT the wave's length — my durations were low

2026-08-26. I published two artifacts using last cumulative sample ÷ sample rate as the duration. That is wrong, and this is the measurement that shows it.

Trying to pin down w0, I decoded leading waves and found the output matched neither trailer word. Following that into the RIFF waves, where the extent is certain, the decoded sample count exceeds the seek table's last cumulative sample by a median 9.7 % — far too much to be rounding.

The tiebreak is the bank's own PsuedoBytesPerSec field, which gives a duration as data_bytes / PBPS and is read, not decoded. Over 14 banks:

comparison	mean absolute difference
PBPS vs the seek-table duration	0.287 s
PBPS vs the decoded duration	0.007 s

Two independent quantities — the bank's declared byte rate and an actual FFmpeg decode — agree with each other to seven milliseconds and both disagree with the seek total. The seek table's last entry is therefore not the wave's sample count; it is the last seek point, which stops short of the end.

Corrected, and both artifacts regenerated with data_bytes / PsuedoBytesPerSec:

• ../data/voice-bank-manifest.txt — total audio 408.3 minutes, not the 390.9 I reported. A 4.3 % understatement in aggregate; the per-bank median error was 9.7 %, but long banks dominate the total and are proportionally more accurate.
• ../data/stage-dialogue-with-durations.txt — every line's timing rises, e.g. "They got Leader!" from 1.78/2.46 s to 2.25/2.93 s.

⚠️ What made this hard to catch: the seek total looked right. It gave BGM tracks of 2.4 minutes, radio chatter of 2.8 seconds, cutscenes of 11 minutes — a set of numbers that sorted themselves into exactly the right shapes, which I cited as the chain validating itself. It was validating the structure and not the scale: a uniform 10 % error preserves every ratio I checked. A self-consistency check cannot catch a systematic factor, and I should not have read it as confirmation of the value.

✅ w0 and w1 identified — they are the last two seek-table entries

Settled. Both trailer words are a verbatim copy of the tail of the leading wave's own seek table:

w0 == table[-2]   282 / 282
w1 == table[-1]   282 / 282

packets  w0        w1        table[-2]  table[-1]
63       409 600   445 440   409 600    445 440
61       375 808   410 624   375 808    410 624
12        68 608    75 264    68 608     75 264

That closes the question and disposes of the "usable length or loop end" reading of w0 — it is simply the previous seek point. It also explains, without needing a separate fact, why w1 − w0 is always a whole multiple of 512: consecutive seek points advance by whole 512-sample XMA1 frames, so any two adjacent entries differ by a whole number of them. What looked like a meaningful constraint was a property of the table it was copied from.

Consistent with the section above, neither word is the wave's true length: for the same banks, data_bytes / PsuedoBytesPerSec gives 481 321 / 410 525 / 81 383 samples against w1 of 445 440 / 410 624 / 75 264. w1 lands within 512 of the true length in only 9 of 282.

🟡 The scattered bytes are an XACT-shaped cue record

2026-08-26. The ~40 remaining non-zero bytes are not noise; they are a small structured record in three runs at roughly +1790, +3840 and +7940 within the block. Two entries side by side:

+1790  2138 00000011 00000020 00000001 00000048
+1814  08000001a0c80000 2138 00000005 0010 0004 3f800000 3f80...
+3838  2138 00000011 00000001 ... 2138 00000011 ... 2138 ffffffff ... 01
+7935  00000001 00000002 00000002 00000064

+1798  214b 00000011 00000020 00000001 00000048   (the next such entry)

Measured across all 282:

the leading 16-bit value names a real SOUNDS cue	282 / 282 (100 %)
the block contains 3f800000 3f80… — two IEEE 1.0 floats	281
the block contains the tail 01 / 02 / 02 / 0x64	281

Two unit floats and a 100 are the shape of volume, pitch and priority — this reads as an XACT cue record. That is a reading of the shape and is marked 🟡; the values are all defaults, so nothing here varies enough to prove it.

❌ The id is not this entry's own cue. It is a real id, but consistently a different, higher one:

entry BR01_02     id 8501  ->  field 8504 = BR02_01
entry BR03_06     id 8518  ->  field 8523 = BR04_04
entry BR09_04     id 8553  ->  field 8558 = BR10_03
entry VOICE_A_027 id 5027  ->  field 5036 = VOICE_A_036

The offsets vary, so it is not a fixed stride.

❌ The chain reading is refuted. I noticed BR09_04's field names BR10_03, which is itself the next exception entry, and flagged it as suggestive but untested. Tested: sorting all 282 by offset, entry[i].field == entry[i+1]'s own id in 8 of 281 (2.8 %) — indistinguishable from coincidence, and BR09_04 was one of the eight. Recording it because it is exactly the kind of pattern that reads as a discovery when spotted in a sample of one.

The offset from the entry's own id is broadly spread — 7 to 14 and beyond, peaking at 9–11 — so the field is near the entry's id without standing in any fixed relation to it:

BR01_02      own 8501  field 8504  = BR02_01
VOICE_A_027  own 5027  field 5036  = VOICE_A_036
VOICE_A_152  own 5152  field 5166  = VOICE_A_166

❔ Not settled: which cue the id refers to and why, and what the 0x11, 0x20, 0x48, 0x0010, 0x0004 constants are. What is settled is that the block is a populated metadata record naming a real cue, not padding — which is the practical point for anyone parsing past it.