FA-49486 / PCM sample encoding / Open access
Riff pcm data spans: append data chunks · case 01
Later PCM chunks overwrite earlier sample spans.
ROOT CAUSE
Later PCM chunks overwrite earlier sample spans.
VERIFIED REPAIR
Use the stated conversion contract at append data chunks.
Unsuccessful approach: Including alignment padding adds non-sample bytes to each odd data chunk.
Case contract
Locate PCM spans in a bounded RIFF-like list of chunk descriptors with eight-byte headers and even-byte padding, requiring a preceding format chunk.
Why this case matters
Offline PCM interchange uses these exact bounded packet and sample representation decisions.
1 / The failure
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(chunks, base):
cursor=base
spans=[]
format_seen=False
for tag,size in chunks:
data_start=cursor+8
if tag=='fmt ':
format_seen=True
if tag=='data' and format_seen:
spans=[[data_start,size]]
cursor=data_start+size+(size&1)
return [spans,cursor]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('oracle 1', solve(*([['fmt ', 16], ['data', 3], ['data', 2]], 12)), [[[44, 3], [56, 2]], 58])
check('oracle 2', solve(*([['JUNK', 3], ['fmt ', 16], ['data', 4]], 12)), [[[56, 4]], 60])
check('oracle 3', solve(*([['data', 4], ['fmt ', 16], ['data', 2]], 0)), [[[44, 2]], 46])
check('oracle 4', solve(*([], 12)), [[], 12])
check('oracle 5', solve(*([['fmt ', 18], ['LIST', 5], ['data', 0]], 12)), [[[60, 0]], 60])
check('oracle 6', solve(*([['fmt ', 16], ['data', 1], ['JUNK', 0], ['data', 1]], 0)), [[[32, 1], [50, 1]], 52])
check('oracle 7', solve(*([['JUNK', 0]], 0)), [[], 8])
if N == 1: check('variant packet 1', solve(*[[['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2]], 12]), [[[44, 3], [56, 2], [90, 3], [102, 2]], 104])
if N == 2: check('variant packet 2', solve(*[[['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2]], 12]), [[[44, 3], [56, 2], [90, 3], [102, 2], [136, 3], [148, 2]], 150])
if N == 3: check('variant packet 3', solve(*[[['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2]], 12]), [[[44, 3], [56, 2], [90, 3], [102, 2], [136, 3], [148, 2], [182, 3], [194, 2]], 196])
if N == 4: check('variant packet 4', solve(*[[['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2]], 12]), [[[44, 3], [56, 2], [90, 3], [102, 2], [136, 3], [148, 2], [182, 3], [194, 2], [228, 3], [240, 2]], 242])
if N == 5: check('variant packet 5', solve(*[[['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2]], 12]), [[[44, 3], [56, 2], [90, 3], [102, 2], [136, 3], [148, 2], [182, 3], [194, 2], [228, 3], [240, 2], [274, 3], [286, 2]], 288])
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| oracle 1 | [[[56, 2]], 58] | [[[44, 3], [56, 2]], 58] | Failed |
| oracle 2 | [[[56, 4]], 60] | [[[56, 4]], 60] | Passed |
| oracle 3 | [[[44, 2]], 46] | [[[44, 2]], 46] | Passed |
| oracle 4 | [[], 12] | [[], 12] | Passed |
| oracle 5 | [[[60, 0]], 60] | [[[60, 0]], 60] | Passed |
| oracle 6 | [[[50, 1]], 52] | [[[32, 1], [50, 1]], 52] | Failed |
| oracle 7 | [[], 8] | [[], 8] | Passed |
| variant packet 1 | [[[102, 2]], 104] | [[[44, 3], [56, 2], [90, 3], [102, 2]], 104] | Failed |
SHA-256 / 03bb51f1d56b445383125d4d2bb08d5d1ee3168f1af1cd17e15fecb03cf8881d
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(chunks, base):
cursor=base
spans=[]
format_seen=False
for tag,size in chunks:
data_start=cursor+8
if tag=='fmt ':
format_seen=True
if tag=='data' and format_seen:
spans.append([data_start,size+(size&1)])
cursor=data_start+size+(size&1)
return [spans,cursor]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('oracle 1', solve(*([['fmt ', 16], ['data', 3], ['data', 2]], 12)), [[[44, 3], [56, 2]], 58])
check('oracle 2', solve(*([['JUNK', 3], ['fmt ', 16], ['data', 4]], 12)), [[[56, 4]], 60])
check('oracle 3', solve(*([['data', 4], ['fmt ', 16], ['data', 2]], 0)), [[[44, 2]], 46])
check('oracle 4', solve(*([], 12)), [[], 12])
check('oracle 5', solve(*([['fmt ', 18], ['LIST', 5], ['data', 0]], 12)), [[[60, 0]], 60])
check('oracle 6', solve(*([['fmt ', 16], ['data', 1], ['JUNK', 0], ['data', 1]], 0)), [[[32, 1], [50, 1]], 52])
check('oracle 7', solve(*([['JUNK', 0]], 0)), [[], 8])
if N == 1: check('variant packet 1', solve(*[[['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2]], 12]), [[[44, 3], [56, 2], [90, 3], [102, 2]], 104])
if N == 2: check('variant packet 2', solve(*[[['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2]], 12]), [[[44, 3], [56, 2], [90, 3], [102, 2], [136, 3], [148, 2]], 150])
if N == 3: check('variant packet 3', solve(*[[['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2]], 12]), [[[44, 3], [56, 2], [90, 3], [102, 2], [136, 3], [148, 2], [182, 3], [194, 2]], 196])
if N == 4: check('variant packet 4', solve(*[[['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2]], 12]), [[[44, 3], [56, 2], [90, 3], [102, 2], [136, 3], [148, 2], [182, 3], [194, 2], [228, 3], [240, 2]], 242])
if N == 5: check('variant packet 5', solve(*[[['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2]], 12]), [[[44, 3], [56, 2], [90, 3], [102, 2], [136, 3], [148, 2], [182, 3], [194, 2], [228, 3], [240, 2], [274, 3], [286, 2]], 288])
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| oracle 1 | [[[44, 4], [56, 2]], 58] | [[[44, 3], [56, 2]], 58] | Failed |
| oracle 2 | [[[56, 4]], 60] | [[[56, 4]], 60] | Passed |
| oracle 3 | [[[44, 2]], 46] | [[[44, 2]], 46] | Passed |
| oracle 4 | [[], 12] | [[], 12] | Passed |
| oracle 5 | [[[60, 0]], 60] | [[[60, 0]], 60] | Passed |
| oracle 6 | [[[32, 2], [50, 2]], 52] | [[[32, 1], [50, 1]], 52] | Failed |
| oracle 7 | [[], 8] | [[], 8] | Passed |
| variant packet 1 | [[[44, 4], [56, 2], [90, 4], [102, 2]], 104] | [[[44, 3], [56, 2], [90, 3], [102, 2]], 104] | Failed |
SHA-256 / bd85f4e241b3f5618321837dab76bc6f7f7b652170a7b37cdd6c279af9e7f6ef
3 / The verified repair
Exit 0"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(chunks, base):
cursor=base
spans=[]
format_seen=False
for tag,size in chunks:
data_start=cursor+8
if tag=='fmt ':
format_seen=True
if tag=='data' and format_seen:
spans.append([data_start,size])
cursor=data_start+size+(size&1)
return [spans,cursor]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('oracle 1', solve(*([['fmt ', 16], ['data', 3], ['data', 2]], 12)), [[[44, 3], [56, 2]], 58])
check('oracle 2', solve(*([['JUNK', 3], ['fmt ', 16], ['data', 4]], 12)), [[[56, 4]], 60])
check('oracle 3', solve(*([['data', 4], ['fmt ', 16], ['data', 2]], 0)), [[[44, 2]], 46])
check('oracle 4', solve(*([], 12)), [[], 12])
check('oracle 5', solve(*([['fmt ', 18], ['LIST', 5], ['data', 0]], 12)), [[[60, 0]], 60])
check('oracle 6', solve(*([['fmt ', 16], ['data', 1], ['JUNK', 0], ['data', 1]], 0)), [[[32, 1], [50, 1]], 52])
check('oracle 7', solve(*([['JUNK', 0]], 0)), [[], 8])
if N == 1: check('variant packet 1', solve(*[[['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2]], 12]), [[[44, 3], [56, 2], [90, 3], [102, 2]], 104])
if N == 2: check('variant packet 2', solve(*[[['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2]], 12]), [[[44, 3], [56, 2], [90, 3], [102, 2], [136, 3], [148, 2]], 150])
if N == 3: check('variant packet 3', solve(*[[['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2]], 12]), [[[44, 3], [56, 2], [90, 3], [102, 2], [136, 3], [148, 2], [182, 3], [194, 2]], 196])
if N == 4: check('variant packet 4', solve(*[[['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2]], 12]), [[[44, 3], [56, 2], [90, 3], [102, 2], [136, 3], [148, 2], [182, 3], [194, 2], [228, 3], [240, 2]], 242])
if N == 5: check('variant packet 5', solve(*[[['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2], ['fmt ', 16], ['data', 3], ['data', 2]], 12]), [[[44, 3], [56, 2], [90, 3], [102, 2], [136, 3], [148, 2], [182, 3], [194, 2], [228, 3], [240, 2], [274, 3], [286, 2]], 288])
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| oracle 1 | [[[44, 3], [56, 2]], 58] | [[[44, 3], [56, 2]], 58] | Passed |
| oracle 2 | [[[56, 4]], 60] | [[[56, 4]], 60] | Passed |
| oracle 3 | [[[44, 2]], 46] | [[[44, 2]], 46] | Passed |
| oracle 4 | [[], 12] | [[], 12] | Passed |
| oracle 5 | [[[60, 0]], 60] | [[[60, 0]], 60] | Passed |
| oracle 6 | [[[32, 1], [50, 1]], 52] | [[[32, 1], [50, 1]], 52] | Passed |
| oracle 7 | [[], 8] | [[], 8] | Passed |
| variant packet 1 | [[[44, 3], [56, 2], [90, 3], [102, 2]], 104] | [[[44, 3], [56, 2], [90, 3], [102, 2]], 104] | Passed |
SHA-256 / eac91c84b33f2cfd7b834d9fec20f96fd86f6e59e5dab3bec33ec23ae4c1b781
Verification & scope
Stipulated finite model; no claim of hardware timing or full file-format conformance. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.
Observations recorded using Python 3.12.14 at 2026-09-29T14:45:00.410271+00:00.
Case digest / fb37b9cda8573a2f7c949152ba24d9461b8ce80efef1f7f49840b2f0b1cae89d