FA-81826 / MIDI event timing / Open access

Event placement inside an audio render buffer: event sample position truncated · case 01

Events between two samples always land on the earlier sample; a half-sample event plays early.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The time-to-sample conversion floors instead of rounding half up.

VERIFIED REPAIR

Restore the sample rounding step so that it reads `(2 * us * sr + 1000000) // 2000000`.

Unsuccessful approach: Rounding up any fraction moves events that are just past a sample to the next sample.

Case contract

Input [sample_rate, buffer_start_sample, buffer_size, event_times_us]. Each event maps to sample position us*rate/1000000 rounded half up. Positions before the buffer start are "late", positions at or after start+size are "future", otherwise the offset within the buffer. Invalid rate or size returns None.

Why this case matters

MIDI sequencers, file readers and synth drivers depend on exact event ordering and tick/time arithmetic.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    if not isinstance(x, list) or len(x) != 4:
        return None
    sr, start, size, events = x
    if sr <= 0 or size <= 0:
        return None
    out = []
    for us in events:
        pos = us * sr // 1000000
        if pos < start:
            out.append('late')
        elif pos >= start + size:
            out.append('future')
        else:
            out.append(pos - start)
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[([48000, 0, 256, [0, 1000, 5333, 5334]], [0, 48, 'future', 'future']), ([48000, 480, 256, [10000, 10010, 15332, 15333]], [0, 0, 'future', 'future']), ([44100, 441, 128, [10000, 10011, 12902, 12903]], [0, 0, 'future', 'future']), ([48000, 48000, 512, [1000000, 1010667, 1010656, 999990]], [0, 'future', 511, 0]), ([1000, 10, 5, [9500, 10000, 14499, 14500]], [0, 0, 4, 'future']), ([48000, 0, 64, [10, 11, 1333, 1343]], [0, 1, 'future', 'future']), ([48000, 0, 0, [0]], None), ([0, 0, 10, [0]], None)], [([48000, 480, 256, [10000, 10010, 15332, 15333]], [0, 0, 'future', 'future']), ([44100, 441, 128, [10000, 10011, 12902, 12903]], [0, 0, 'future', 'future']), ([48000, 48000, 512, [1000000, 1010667, 1010656, 999990]], [0, 'future', 511, 0]), ([1000, 10, 5, [9500, 10000, 14499, 14500]], [0, 0, 4, 'future']), ([48000, 0, 64, [10, 11, 1333, 1343]], [0, 1, 'future', 'future']), ([44100, 1024, 256, [23220, 23232, 29025, 29037]], [0, 1, 'future', 'future']), ([8000, 100, 10, [12500, 12562, 13687, 13688]], [0, 0, 9, 'future']), ([96000, 960, 96, [10000, 10005, 10995, 11000]], [0, 0, 'future', 'future'])], [([44100, 441, 128, [10000, 10011, 12902, 12903]], [0, 0, 'future', 'future']), ([48000, 48000, 512, [1000000, 1010667, 1010656, 999990]], [0, 'future', 511, 0]), ([1000, 10, 5, [9500, 10000, 14499, 14500]], [0, 0, 4, 'future']), ([48000, 0, 64, [10, 11, 1333, 1343]], [0, 1, 'future', 'future']), ([44100, 1024, 256, [23220, 23232, 29025, 29037]], [0, 1, 'future', 'future']), ([8000, 100, 10, [12500, 12562, 13687, 13688]], [0, 0, 9, 'future']), ([96000, 960, 96, [10000, 10005, 10995, 11000]], [0, 0, 'future', 'future']), ([1000, 0, 4, [499, 500, 3499, 3500]], [0, 1, 3, 'future'])], [([48000, 48000, 512, [1000000, 1010667, 1010656, 999990]], [0, 'future', 511, 0]), ([1000, 10, 5, [9500, 10000, 14499, 14500]], [0, 0, 4, 'future']), ([48000, 0, 64, [10, 11, 1333, 1343]], [0, 1, 'future', 'future']), ([8000, 100, 10, [12500, 12562, 13687, 13688]], [0, 0, 9, 'future']), ([48000, 0, 0, [0]], None), ([0, 0, 10, [0]], None), ([96000, 960, 96, [10000, 10005, 10995, 11000]], [0, 0, 'future', 'future']), ([1000, 0, 4, [499, 500, 3499, 3500]], [0, 1, 3, 'future'])], [([48000, 0, 256, [0, 1000, 5333, 5334]], [0, 48, 'future', 'future']), ([48000, 480, 256, [10000, 10010, 15332, 15333]], [0, 0, 'future', 'future']), ([1000, 10, 5, [9500, 10000, 14499, 14500]], [0, 0, 4, 'future']), ([48000, 0, 64, [10, 11, 1333, 1343]], [0, 1, 'future', 'future']), ([44100, 1024, 256, [23220, 23232, 29025, 29037]], [0, 1, 'future', 'future']), ([48000, 0, 0, [0]], None), ([0, 0, 10, [0]], None), ([96000, 960, 96, [10000, 10005, 10995, 11000]], [0, 0, 'future', 'future'])]]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("oracle %d" % i, solve(args), expected)
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 0	`[0, 48, 255, 'future']`	`[0, 48, 'future', 'future']`	Failed
oracle 1	`[0, 0, 255, 255]`	`[0, 0, 'future', 'future']`	Failed
oracle 2	`[0, 0, 127, 'future']`	`[0, 0, 'future', 'future']`	Failed
oracle 3	`[0, 'future', 511, 'late']`	`[0, 'future', 511, 0]`	Failed
oracle 4	`['late', 0, 4, 4]`	`[0, 0, 4, 'future']`	Failed
oracle 5	`[0, 0, 63, 'future']`	`[0, 1, 'future', 'future']`	Failed
oracle 6	`None`	`None`	Passed
oracle 7	`None`	`None`	Passed

SHA-256 / 32a5bba1b64cd744458dec973f6a3ef483927951a3ffb0c47cf102f5b74c2a77

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    if not isinstance(x, list) or len(x) != 4:
        return None
    sr, start, size, events = x
    if sr <= 0 or size <= 0:
        return None
    out = []
    for us in events:
        pos = (us * sr + 999999) // 1000000
        if pos < start:
            out.append('late')
        elif pos >= start + size:
            out.append('future')
        else:
            out.append(pos - start)
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[([48000, 0, 256, [0, 1000, 5333, 5334]], [0, 48, 'future', 'future']), ([48000, 480, 256, [10000, 10010, 15332, 15333]], [0, 0, 'future', 'future']), ([44100, 441, 128, [10000, 10011, 12902, 12903]], [0, 0, 'future', 'future']), ([48000, 48000, 512, [1000000, 1010667, 1010656, 999990]], [0, 'future', 511, 0]), ([1000, 10, 5, [9500, 10000, 14499, 14500]], [0, 0, 4, 'future']), ([48000, 0, 64, [10, 11, 1333, 1343]], [0, 1, 'future', 'future']), ([48000, 0, 0, [0]], None), ([0, 0, 10, [0]], None)], [([48000, 480, 256, [10000, 10010, 15332, 15333]], [0, 0, 'future', 'future']), ([44100, 441, 128, [10000, 10011, 12902, 12903]], [0, 0, 'future', 'future']), ([48000, 48000, 512, [1000000, 1010667, 1010656, 999990]], [0, 'future', 511, 0]), ([1000, 10, 5, [9500, 10000, 14499, 14500]], [0, 0, 4, 'future']), ([48000, 0, 64, [10, 11, 1333, 1343]], [0, 1, 'future', 'future']), ([44100, 1024, 256, [23220, 23232, 29025, 29037]], [0, 1, 'future', 'future']), ([8000, 100, 10, [12500, 12562, 13687, 13688]], [0, 0, 9, 'future']), ([96000, 960, 96, [10000, 10005, 10995, 11000]], [0, 0, 'future', 'future'])], [([44100, 441, 128, [10000, 10011, 12902, 12903]], [0, 0, 'future', 'future']), ([48000, 48000, 512, [1000000, 1010667, 1010656, 999990]], [0, 'future', 511, 0]), ([1000, 10, 5, [9500, 10000, 14499, 14500]], [0, 0, 4, 'future']), ([48000, 0, 64, [10, 11, 1333, 1343]], [0, 1, 'future', 'future']), ([44100, 1024, 256, [23220, 23232, 29025, 29037]], [0, 1, 'future', 'future']), ([8000, 100, 10, [12500, 12562, 13687, 13688]], [0, 0, 9, 'future']), ([96000, 960, 96, [10000, 10005, 10995, 11000]], [0, 0, 'future', 'future']), ([1000, 0, 4, [499, 500, 3499, 3500]], [0, 1, 3, 'future'])], [([48000, 48000, 512, [1000000, 1010667, 1010656, 999990]], [0, 'future', 511, 0]), ([1000, 10, 5, [9500, 10000, 14499, 14500]], [0, 0, 4, 'future']), ([48000, 0, 64, [10, 11, 1333, 1343]], [0, 1, 'future', 'future']), ([8000, 100, 10, [12500, 12562, 13687, 13688]], [0, 0, 9, 'future']), ([48000, 0, 0, [0]], None), ([0, 0, 10, [0]], None), ([96000, 960, 96, [10000, 10005, 10995, 11000]], [0, 0, 'future', 'future']), ([1000, 0, 4, [499, 500, 3499, 3500]], [0, 1, 3, 'future'])], [([48000, 0, 256, [0, 1000, 5333, 5334]], [0, 48, 'future', 'future']), ([48000, 480, 256, [10000, 10010, 15332, 15333]], [0, 0, 'future', 'future']), ([1000, 10, 5, [9500, 10000, 14499, 14500]], [0, 0, 4, 'future']), ([48000, 0, 64, [10, 11, 1333, 1343]], [0, 1, 'future', 'future']), ([44100, 1024, 256, [23220, 23232, 29025, 29037]], [0, 1, 'future', 'future']), ([48000, 0, 0, [0]], None), ([0, 0, 10, [0]], None), ([96000, 960, 96, [10000, 10005, 10995, 11000]], [0, 0, 'future', 'future'])]]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("oracle %d" % i, solve(args), expected)
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 0	`[0, 48, 'future', 'future']`	`[0, 48, 'future', 'future']`	Passed
oracle 1	`[0, 1, 'future', 'future']`	`[0, 0, 'future', 'future']`	Failed
oracle 2	`[0, 1, 'future', 'future']`	`[0, 0, 'future', 'future']`	Failed
oracle 3	`[0, 'future', 'future', 0]`	`[0, 'future', 511, 0]`	Failed
oracle 4	`[0, 0, 'future', 'future']`	`[0, 0, 4, 'future']`	Failed
oracle 5	`[1, 1, 'future', 'future']`	`[0, 1, 'future', 'future']`	Failed
oracle 6	`None`	`None`	Passed
oracle 7	`None`	`None`	Passed

SHA-256 / b9292e652f3cc9c987af0161ac02c4806b0cbeb3b0185e058b6c5fa5366e5847

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    if not isinstance(x, list) or len(x) != 4:
        return None
    sr, start, size, events = x
    if sr <= 0 or size <= 0:
        return None
    out = []
    for us in events:
        pos = (2 * us * sr + 1000000) // 2000000
        if pos < start:
            out.append('late')
        elif pos >= start + size:
            out.append('future')
        else:
            out.append(pos - start)
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[([48000, 0, 256, [0, 1000, 5333, 5334]], [0, 48, 'future', 'future']), ([48000, 480, 256, [10000, 10010, 15332, 15333]], [0, 0, 'future', 'future']), ([44100, 441, 128, [10000, 10011, 12902, 12903]], [0, 0, 'future', 'future']), ([48000, 48000, 512, [1000000, 1010667, 1010656, 999990]], [0, 'future', 511, 0]), ([1000, 10, 5, [9500, 10000, 14499, 14500]], [0, 0, 4, 'future']), ([48000, 0, 64, [10, 11, 1333, 1343]], [0, 1, 'future', 'future']), ([48000, 0, 0, [0]], None), ([0, 0, 10, [0]], None)], [([48000, 480, 256, [10000, 10010, 15332, 15333]], [0, 0, 'future', 'future']), ([44100, 441, 128, [10000, 10011, 12902, 12903]], [0, 0, 'future', 'future']), ([48000, 48000, 512, [1000000, 1010667, 1010656, 999990]], [0, 'future', 511, 0]), ([1000, 10, 5, [9500, 10000, 14499, 14500]], [0, 0, 4, 'future']), ([48000, 0, 64, [10, 11, 1333, 1343]], [0, 1, 'future', 'future']), ([44100, 1024, 256, [23220, 23232, 29025, 29037]], [0, 1, 'future', 'future']), ([8000, 100, 10, [12500, 12562, 13687, 13688]], [0, 0, 9, 'future']), ([96000, 960, 96, [10000, 10005, 10995, 11000]], [0, 0, 'future', 'future'])], [([44100, 441, 128, [10000, 10011, 12902, 12903]], [0, 0, 'future', 'future']), ([48000, 48000, 512, [1000000, 1010667, 1010656, 999990]], [0, 'future', 511, 0]), ([1000, 10, 5, [9500, 10000, 14499, 14500]], [0, 0, 4, 'future']), ([48000, 0, 64, [10, 11, 1333, 1343]], [0, 1, 'future', 'future']), ([44100, 1024, 256, [23220, 23232, 29025, 29037]], [0, 1, 'future', 'future']), ([8000, 100, 10, [12500, 12562, 13687, 13688]], [0, 0, 9, 'future']), ([96000, 960, 96, [10000, 10005, 10995, 11000]], [0, 0, 'future', 'future']), ([1000, 0, 4, [499, 500, 3499, 3500]], [0, 1, 3, 'future'])], [([48000, 48000, 512, [1000000, 1010667, 1010656, 999990]], [0, 'future', 511, 0]), ([1000, 10, 5, [9500, 10000, 14499, 14500]], [0, 0, 4, 'future']), ([48000, 0, 64, [10, 11, 1333, 1343]], [0, 1, 'future', 'future']), ([8000, 100, 10, [12500, 12562, 13687, 13688]], [0, 0, 9, 'future']), ([48000, 0, 0, [0]], None), ([0, 0, 10, [0]], None), ([96000, 960, 96, [10000, 10005, 10995, 11000]], [0, 0, 'future', 'future']), ([1000, 0, 4, [499, 500, 3499, 3500]], [0, 1, 3, 'future'])], [([48000, 0, 256, [0, 1000, 5333, 5334]], [0, 48, 'future', 'future']), ([48000, 480, 256, [10000, 10010, 15332, 15333]], [0, 0, 'future', 'future']), ([1000, 10, 5, [9500, 10000, 14499, 14500]], [0, 0, 4, 'future']), ([48000, 0, 64, [10, 11, 1333, 1343]], [0, 1, 'future', 'future']), ([44100, 1024, 256, [23220, 23232, 29025, 29037]], [0, 1, 'future', 'future']), ([48000, 0, 0, [0]], None), ([0, 0, 10, [0]], None), ([96000, 960, 96, [10000, 10005, 10995, 11000]], [0, 0, 'future', 'future'])]]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("oracle %d" % i, solve(args), expected)
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 0	`[0, 48, 'future', 'future']`	`[0, 48, 'future', 'future']`	Passed
oracle 1	`[0, 0, 'future', 'future']`	`[0, 0, 'future', 'future']`	Passed
oracle 2	`[0, 0, 'future', 'future']`	`[0, 0, 'future', 'future']`	Passed
oracle 3	`[0, 'future', 511, 0]`	`[0, 'future', 511, 0]`	Passed
oracle 4	`[0, 0, 4, 'future']`	`[0, 0, 4, 'future']`	Passed
oracle 5	`[0, 1, 'future', 'future']`	`[0, 1, 'future', 'future']`	Passed
oracle 6	`None`	`None`	Passed
oracle 7	`None`	`None`	Passed

SHA-256 / e90d6467b973d749e1c99720ffeb9f9228de997e895a02cb305895816d87e822

Verification & scope

A deterministic bounded teaching model with a stipulated toy contract; it is not a complete Standard MIDI File or MIDI 1.0/2.0 implementation. 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 2026-09-29T14:50:06.394724+00:00.

Case digest / b5e9f02a2c75a24807cbdf0e57a99299bf60bd7fe969b5a01e6a1d903af24061