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re: resolve_movie_voice_region starts INSIDE the first stream, 8 of 10 multichannel regions

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Found because the port refused to apply my stream assignment and did the
arithmetic instead: the running decoder's three ADV contexts sum to 3 584 000 B
against a resolved region of 3 114 352 -- 15 % too small to hold them. Two spans,
one wrong, and it was the disc side.

The gap is 238 packets exactly (487 424 B), which is what a start offset looks
like; ctx0 declares 632 packets and the resolver's leading chunk has 394.

Verified against the decoder's own byte_sizes, which cannot be fitted to: at
-238 packets to_xma_riffs yields [1294336, 1118208, 1171456], all three exactly.
It is a real boundary and not the end of a sweep -- at -300 the previous asset's
chunks appear while the three ADV sizes stay stable.

Disc-wide: 24 of 24 single-chunk regions start at a boundary; 8 of 10 three-chunk
regions start mid-stream. The defect is specific to the multichannel case.

The audit's per-movie number is an UPPER BOUND, not the clip -- its stopping rule
is the chunk count changing, and to_xma_riffs absorbs a few packets of the
previous asset first (243 reported for ADV against a true 238). Only ADV has
external ground truth.

Consequence: in those 8 movies the leading chunk is a truncated first stream, not
a spurious artefact, and anything measured on it was measured on a fragment --
including this corpus's own chunk-0 level, though the assignment survives because
its ratio test was chosen to be immune to the clipping.

The resolver is NOT patched. Why the predecessor cue's trailer lands 238 packets
into the next asset is unanswered, and a fix guessed from one movie would be
worse than a documented defect.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Wuu56cE8vJGTBtn1ppsk8v
This commit is contained in:
sylph-decoder
2026-08-30 08:41:22 +00:00
parent 8c71520ab8
commit 3e8235ddbd
6 changed files with 321 additions and 0 deletions
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63
docs/re/data/voice-region-start-audit.txt Normal file
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@@ -0,0 +1,63 @@
movie chunks first chunk clip pkts verdict
ADV 3 806912 243 STARTS MID-STREAM
S00A 3 1323008 243 STARTS MID-STREAM
S01A 3 1153024 243 STARTS MID-STREAM
RT01A 1 284672 0 starts at a boundary
RT01B 1 350208 0 starts at a boundary
RT01C_1 1 352256 0 starts at a boundary
RT01C_2 1 354304 0 starts at a boundary
S02A 3 665600 0 starts at a boundary
S02B 3 430080 243 STARTS MID-STREAM
S02C 3 1867776 243 STARTS MID-STREAM
RT02A 1 321536 0 starts at a boundary
RT02B 1 387072 0 starts at a boundary
RT02C 1 436224 0 starts at a boundary
RT02D_1 1 190464 0 starts at a boundary
RT02D_2 1 243712 0 starts at a boundary
hokyu_LS_s02A 1 51200 0 starts at a boundary
hokyu_LS_s02H 1 38912 0 starts at a boundary
S03A 3 251904 243 STARTS MID-STREAM
RT03A 1 319488 0 starts at a boundary
RT03B 1 266240 0 starts at a boundary
RT03C 1 397312 0 starts at a boundary
RT03D 1 612352 0 starts at a boundary
hokyu_LS_s03A 1 51200 0 starts at a boundary
hokyu_LS_s03H 1 38912 0 starts at a boundary
S04B 3 555008 243 STARTS MID-STREAM
RT04A 1 229376 0 starts at a boundary
RT04B 1 219136 0 starts at a boundary
hokyu_DS_s02A 1 53248 0 starts at a boundary
S05A 3 161792 0 starts at a boundary
RT05A 1 307200 0 starts at a boundary
RT05B 1 344064 0 starts at a boundary
RT05C 1 188416 0 starts at a boundary
hokyu_LS_s02A 1 51200 0 starts at a boundary
S06A 3 350208 243 STARTS MID-STREAM
S06B 3 606208 243 STARTS MID-STREAM
RT06A 1 301056 0 starts at a boundary
RT06B 1 325632 0 starts at a boundary
RT06C 1 227328 0 starts at a boundary
RT06D 1 120832 0 starts at a boundary
hokyu_LS_s06A 1 51200 0 starts at a boundary
hokyu_LS_s06H 1 38912 0 starts at a boundary
S07A 3 503808 243 STARTS MID-STREAM
S07B 3 53248 0 starts at a boundary
RT07A 1 505856 0 starts at a boundary
RT07B 1 258048 0 starts at a boundary
RT07C 1 133120 0 starts at a boundary
hokyu_DS_s07A 1 53248 0 starts at a boundary
hokyu_DS_s07H 1 57344 0 starts at a boundary
RT08A 1 180224 0 starts at a boundary
RT08B 1 174080 0 starts at a boundary
RT08C 1 143360 0 starts at a boundary
hokyu_DS_s08A 1 53248 0 starts at a boundary
S09B 3 176128 243 STARTS MID-STREAM
RT09A 1 307200 0 starts at a boundary
RT09B 1 468992 0 starts at a boundary
RT09C 1 245760 0 starts at a boundary
RT09D 1 385024 0 starts at a boundary
hokyu_LS_s09A 1 53248 0 starts at a boundary
hokyu_LS_s09H 1 38912 0 starts at a boundary
RT10A 1 106496 0 starts at a boundary
RT10B 1 67584 0 starts at a boundary
S11A 3 81920 0 starts at a boundary

47
docs/re/data/voice-region-start-clip.txt Normal file
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# resolve_movie_voice_region starts 238 packets LATE for ADV.
#
# 2026-08-30. Raised by the port agent, whose arithmetic is the whole reason
# this was found: the running decoder's three ADV contexts sum to 3 584 000
# payload bytes, but the resolved region is 3 114 352 -- 15 % too small to
# hold them. One of the two spans was wrong, and it was the disc side.
#
# The gap is a WHOLE NUMBER OF PACKETS, which is what a start offset looks
# like and corruption does not:
# ctx0 declares 632 packets = 1 294 336 B
# the resolver's leading chunk has 394 packets = 806 912 B
# difference 238 packets = 487 424 B
#
# GROUND TRUTH is the running decoder's own byte_sizes. This is not free to
# fit: the span either lands on all three or it does not.
#
resolver says 433930240..437044592 (3114352 B)
decoder wants [1294336, 1118208, 1171456] = 3584000 B payload
- 0 packets (start 433930240): 3 chunk(s) [806912, 1118208, 1171456]
- 100 packets (start 433725440): 3 chunk(s) [1011712, 1118208, 1171456]
- 200 packets (start 433520640): 3 chunk(s) [1216512, 1118208, 1171456]
- 237 packets (start 433444864): 3 chunk(s) [1292288, 1118208, 1171456]
- 238 packets (start 433442816): 3 chunk(s) [1294336, 1118208, 1171456] <== MATCHES THE DECODER
- 239 packets (start 433440768): 3 chunk(s) [1296384, 1118208, 1171456]
- 300 packets (start 433315840): 5 chunk(s) [57344, 45056, 1294336, 1118208, 1171456]
- 400 packets (start 433111040): 8 chunk(s) [59392, 59392, 47104, 47104, 45056, 1294336, 1118208, 1171456]
# -238 is a real boundary, not the end of a sweep: at -300 and -400 the
# PREVIOUS asset's chunks appear (57344, 45056, ...) while the three ADV
# sizes stay exactly stable. The stream starts at -238 and something else
# ends just before it.
# ---------------------------------------------------------------------------
# DISC-WIDE (examples/voice_region_start_audit.rs, full table in
# voice-region-start-audit.txt)
#
# 1-chunk regions: 24 of 24 start at a chunk boundary
# 3-chunk regions: 8 of 10 START MID-STREAM
#
# So the defect is specific to the three-stream (multichannel) voice regions.
#
# ⚠️ The audit's "243" column is an UPPER BOUND on the clip, not the clip. Its
# stopping rule is "step back until the chunk COUNT changes", and to_xma_riffs
# will happily absorb a few packets of the PREVIOUS asset into the first chunk
# before that happens -- for ADV it reports 243 where the decoder-verified
# answer is 238. Only ADV has external ground truth.

8
docs/re/structures/intro-audio-decomposed.md
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@@ -149,6 +149,14 @@ FL/FR residual's **+0.918**, chunk 2 **+0.962** against BL/BR's **+0.929**.
| ctx1 · 1 118 208 | **FC** (LFE silent) |
| ctx2 · 1 171 456 | **BL, BR** |
🔴 **And the identifier this is indexed by does not resolve against the disc.** The
port refused to apply this assignment because the three contexts sum to 3 584 000 B
against a resolved region of 3 114 352. It was right to: the **region start is
wrong**, by 238 packets for `ADV` and on 8 of 10 multichannel regions disc-wide —
[`voice-region-starts-late.md`](voice-region-starts-late.md). The assignment above
still stands (the ratio test was chosen to be immune to the clipping), but chunk 0's
absolute level was measured over 62 % of its stream.
⚠️ **Reach.** Levels, not waveforms — this is an argument from three numbers
agreeing to 0.5 dB and a 1:1 structural match, not from a matched waveform. One
movie, one boot. And chunk 0 is a clipped tail, which is why the ratio test is

87
docs/re/structures/voice-region-starts-late.md Normal file
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@@ -0,0 +1,87 @@
# 🔴 `resolve_movie_voice_region` starts **inside** the first stream — 8 of 10 multichannel regions
**Classification: decoded**, against the running decoder as ground truth for one
movie and a structural check disc-wide. Found because the port agent refused to
apply a result of mine and did the arithmetic instead.
## How it surfaced
I sent the port a stream→channel assignment indexed by `byte_size`. It did not
apply it, and said why:
| | bytes |
|---|---|
| the running decoder's three `ADV` contexts | **3 584 000** |
| the resolved `ADV` voice region | **3 114 352** |
| | **15 % too small to hold them** |
Two spans, one of which was not what the other thought it was. The disc side is
this crate's, and it is the one that was wrong.
## The gap is a whole number of packets
| | |
|---|---|
| `ctx0` declares | **632** packets = 1 294 336 B |
| the resolver's leading chunk has | **394** packets = 806 912 B |
| difference | **238 packets = 487 424 B** |
A whole number of packets is what a **start offset** looks like. Corruption does not
land on 2048-byte multiples.
## Verified against the decoder, which cannot be fitted to
Stepping the region start backwards and re-running `to_xma_riffs`
([`../data/voice-region-start-clip.txt`](../data/voice-region-start-clip.txt)):
```
- 0 packets: [806912, 1118208, 1171456]
- 237 packets: [1292288, 1118208, 1171456]
- 238 packets: [1294336, 1118208, 1171456] <== the decoder's own three sizes
- 239 packets: [1296384, 1118208, 1171456]
- 300 packets: [57344, 45056, 1294336, 1118208, 1171456]
```
✅ **−238 is a real boundary, not the end of a sweep.** At −300 the *previous*
asset's chunks appear (57 344, 45 056) while the three `ADV` sizes stay exactly
stable. The stream begins there and something else ends just before it.
## Disc-wide
[`../data/voice-region-start-audit.txt`](../data/voice-region-start-audit.txt):
| region | starts at a boundary | **starts mid-stream** |
|---|---|---|
| 1 chunk | **24 / 24** | 0 |
| 3 chunks | 2 | **8 / 10** |
**The defect is specific to the three-stream (multichannel) regions.** Every
single-stream region is fine.
⚠️ **The audit's per-movie packet number is an UPPER BOUND, not the clip.** Its
stopping rule is "step back until the chunk *count* changes", and `to_xma_riffs`
absorbs a few packets of the previous asset into the first chunk before that
happens — it reports **243** for `ADV` where the decoder-verified answer is **238**.
Only `ADV` has external ground truth, so only `ADV`'s clip is exact.
## What this means for anyone consuming a voice region
🔴 **In those 8 movies the leading chunk is a truncated first stream, not a spurious
artefact.** Any consumer that drops it as "the leading chunk that matches nothing"
is discarding most of a real stream — and any measurement made *on* it (levels,
correlations against the other chunks) was made on a fragment.
⚠️ **This includes measurements in this corpus.** My own
[`intro-audio-decomposed.md`](intro-audio-decomposed.md) assignment used `ADV`'s
clipped chunk 0; the quantitative argument there survives because it quotes a
**ratio** test explicitly chosen to be immune to the clipping, but the absolute
level for chunk 0 was measured over 62 % of the stream.
## ⚠️ What is NOT fixed here
**The resolver is unchanged.** This page establishes that its start is wrong for
these regions and by how much for one of them; it does not derive the correct rule.
`voice_region_chunks.rs`'s own note says the region *"starts at the PREDECESSOR
cue's trailer"* — so the question is why that trailer lands 238 packets into the
next asset, and that is not answered. Recorded rather than patched, because a fix
guessed from one movie would be worse than a documented defect.