FA-81381 / MIDI event timing / Open access

Standard MIDI File header chunk reader: chunk length read little-endian · case 01

Every normal header (length 00 00 00 06) is rejected because the length reads as 100663296.

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

ROOT CAUSE

The 32-bit chunk length is assembled little-endian although SMF chunk lengths are big-endian.

VERIFIED REPAIR

Restore the chunk length byte order step so that it reads `(x[4] << 24) | (x[5] << 16) | (x[6] << 8) | x[7]`.

Unsuccessful approach: Reading only the low 16 bits accepts a header whose declared length is 65542 but whose bytes are missing.

Case contract

Input the bytes of a header chunk: "MThd", a 32-bit big-endian length (>= 6; extra bytes ignored but must be present), 16-bit format (0, 1, 2), 16-bit track count (nonzero; exactly 1 for format 0) and 16-bit division. If bit 15 of division is set, the high byte is a negative two's-complement frame rate (24, 25, 29, 30) and the low byte ticks per frame; otherwise division is ticks per quarter note (nonzero). Return a dict or 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) < 14 or x[:4] != [77, 84, 104, 100]:
        return None
    length = x[4] | (x[5] << 8) | (x[6] << 16) | (x[7] << 24)
    if length < 6 or len(x) < 8 + length:
        return None
    fmt = (x[8] << 8) | x[9]
    ntrks = (x[10] << 8) | x[11]
    division = (x[12] << 8) | x[13]
    if fmt not in (0, 1, 2) or ntrks == 0 or (fmt == 0 and ntrks != 1):
        return None
    if division & 0x8000:
        fps = 256 - x[12]
        if fps not in (24, 25, 29, 30):
            return None
        return {'format': fmt, 'tracks': ntrks, 'fps': fps, 'ticks_per_frame': x[13]}
    if division == 0:
        return None
    return {'format': fmt, 'tracks': ntrks, 'ppq': division}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 2, 1, 224], {'format': 1, 'tracks': 2, 'ppq': 480}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 0, 0, 2, 0, 96], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 3, 231, 40], {'format': 1, 'tracks': 3, 'fps': 25, 'ticks_per_frame': 40}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 230, 4], None), ([77, 84, 104, 100, 0, 0, 0, 8, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 5, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 1, 0, 6, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 3, 0, 2, 1, 224], None)], [([77, 84, 104, 100, 0, 0, 0, 6, 0, 0, 0, 1, 0, 96], {'format': 0, 'tracks': 1, 'ppq': 96}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 232, 80], {'format': 1, 'tracks': 1, 'fps': 24, 'ticks_per_frame': 80}), ([77, 84, 104, 100, 0, 0, 0, 5, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 1, 0, 6, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 3, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 0, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 2, 0, 0], None), ([77, 84, 105, 100, 0, 0, 0, 6, 0, 1, 0, 2, 1, 224], None)], [([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 2, 1, 224], {'format': 1, 'tracks': 2, 'ppq': 480}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 3, 231, 40], {'format': 1, 'tracks': 3, 'fps': 25, 'ticks_per_frame': 40}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 227, 4], {'format': 1, 'tracks': 1, 'fps': 29, 'ticks_per_frame': 4}), ([77, 84, 104, 100, 0, 1, 0, 6, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 2, 0, 0], None), ([77, 84, 105, 100, 0, 0, 0, 6, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 2, 128, 0], None)], [([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 2, 1, 224], {'format': 1, 'tracks': 2, 'ppq': 480}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 0, 0, 1, 0, 96], {'format': 0, 'tracks': 1, 'ppq': 96}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 3, 231, 40], {'format': 1, 'tracks': 3, 'fps': 25, 'ticks_per_frame': 40}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 232, 80], {'format': 1, 'tracks': 1, 'fps': 24, 'ticks_per_frame': 80}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 227, 4], {'format': 1, 'tracks': 1, 'fps': 29, 'ticks_per_frame': 4}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 226, 100], {'format': 1, 'tracks': 1, 'fps': 30, 'ticks_per_frame': 100}), ([77, 84, 104, 100, 0, 1, 0, 6, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 2, 128, 0], None)], [([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 3, 231, 40], {'format': 1, 'tracks': 3, 'fps': 25, 'ticks_per_frame': 40}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 232, 80], {'format': 1, 'tracks': 1, 'fps': 24, 'ticks_per_frame': 80}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 227, 4], {'format': 1, 'tracks': 1, 'fps': 29, 'ticks_per_frame': 4}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 226, 100], {'format': 1, 'tracks': 1, 'fps': 30, 'ticks_per_frame': 100}), ([77, 84, 104, 100, 0, 0, 0, 8, 0, 1, 0, 2, 1, 224, 0, 0], {'format': 1, 'tracks': 2, 'ppq': 480}), ([77, 84, 104, 100, 0, 1, 0, 6, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 2, 0, 5, 0, 120], {'format': 2, 'tracks': 5, 'ppq': 120}), ([77, 84, 104, 100, 0, 0, 0, 7, 0, 1, 0, 2, 1, 224, 9], {'format': 1, 'tracks': 2, 'ppq': 480})]]
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	`None`	`{'format': 1, 'ppq': 480, 'tracks': 2}`	Failed
oracle 1	`None`	`None`	Passed
oracle 2	`None`	`{'format': 1, 'fps': 25, 'ticks_per_frame': 40, 'tracks': 3}`	Failed
oracle 3	`None`	`None`	Passed
oracle 4	`None`	`None`	Passed
oracle 5	`None`	`None`	Passed
oracle 6	`None`	`None`	Passed
oracle 7	`None`	`None`	Passed

SHA-256 / 6ad3d0388e1687efd6d0b19100b73edbdcfd89721311fffdd5425edfb2cfb682

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) < 14 or x[:4] != [77, 84, 104, 100]:
        return None
    length = (x[6] << 8) | x[7]
    if length < 6 or len(x) < 8 + length:
        return None
    fmt = (x[8] << 8) | x[9]
    ntrks = (x[10] << 8) | x[11]
    division = (x[12] << 8) | x[13]
    if fmt not in (0, 1, 2) or ntrks == 0 or (fmt == 0 and ntrks != 1):
        return None
    if division & 0x8000:
        fps = 256 - x[12]
        if fps not in (24, 25, 29, 30):
            return None
        return {'format': fmt, 'tracks': ntrks, 'fps': fps, 'ticks_per_frame': x[13]}
    if division == 0:
        return None
    return {'format': fmt, 'tracks': ntrks, 'ppq': division}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 2, 1, 224], {'format': 1, 'tracks': 2, 'ppq': 480}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 0, 0, 2, 0, 96], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 3, 231, 40], {'format': 1, 'tracks': 3, 'fps': 25, 'ticks_per_frame': 40}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 230, 4], None), ([77, 84, 104, 100, 0, 0, 0, 8, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 5, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 1, 0, 6, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 3, 0, 2, 1, 224], None)], [([77, 84, 104, 100, 0, 0, 0, 6, 0, 0, 0, 1, 0, 96], {'format': 0, 'tracks': 1, 'ppq': 96}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 232, 80], {'format': 1, 'tracks': 1, 'fps': 24, 'ticks_per_frame': 80}), ([77, 84, 104, 100, 0, 0, 0, 5, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 1, 0, 6, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 3, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 0, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 2, 0, 0], None), ([77, 84, 105, 100, 0, 0, 0, 6, 0, 1, 0, 2, 1, 224], None)], [([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 2, 1, 224], {'format': 1, 'tracks': 2, 'ppq': 480}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 3, 231, 40], {'format': 1, 'tracks': 3, 'fps': 25, 'ticks_per_frame': 40}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 227, 4], {'format': 1, 'tracks': 1, 'fps': 29, 'ticks_per_frame': 4}), ([77, 84, 104, 100, 0, 1, 0, 6, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 2, 0, 0], None), ([77, 84, 105, 100, 0, 0, 0, 6, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 2, 128, 0], None)], [([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 2, 1, 224], {'format': 1, 'tracks': 2, 'ppq': 480}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 0, 0, 1, 0, 96], {'format': 0, 'tracks': 1, 'ppq': 96}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 3, 231, 40], {'format': 1, 'tracks': 3, 'fps': 25, 'ticks_per_frame': 40}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 232, 80], {'format': 1, 'tracks': 1, 'fps': 24, 'ticks_per_frame': 80}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 227, 4], {'format': 1, 'tracks': 1, 'fps': 29, 'ticks_per_frame': 4}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 226, 100], {'format': 1, 'tracks': 1, 'fps': 30, 'ticks_per_frame': 100}), ([77, 84, 104, 100, 0, 1, 0, 6, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 2, 128, 0], None)], [([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 3, 231, 40], {'format': 1, 'tracks': 3, 'fps': 25, 'ticks_per_frame': 40}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 232, 80], {'format': 1, 'tracks': 1, 'fps': 24, 'ticks_per_frame': 80}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 227, 4], {'format': 1, 'tracks': 1, 'fps': 29, 'ticks_per_frame': 4}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 226, 100], {'format': 1, 'tracks': 1, 'fps': 30, 'ticks_per_frame': 100}), ([77, 84, 104, 100, 0, 0, 0, 8, 0, 1, 0, 2, 1, 224, 0, 0], {'format': 1, 'tracks': 2, 'ppq': 480}), ([77, 84, 104, 100, 0, 1, 0, 6, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 2, 0, 5, 0, 120], {'format': 2, 'tracks': 5, 'ppq': 120}), ([77, 84, 104, 100, 0, 0, 0, 7, 0, 1, 0, 2, 1, 224, 9], {'format': 1, 'tracks': 2, 'ppq': 480})]]
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	`{'format': 1, 'ppq': 480, 'tracks': 2}`	`{'format': 1, 'ppq': 480, 'tracks': 2}`	Passed
oracle 1	`None`	`None`	Passed
oracle 2	`{'format': 1, 'fps': 25, 'ticks_per_frame': 40, 'tracks': 3}`	`{'format': 1, 'fps': 25, 'ticks_per_frame': 40, 'tracks': 3}`	Passed
oracle 3	`None`	`None`	Passed
oracle 4	`None`	`None`	Passed
oracle 5	`None`	`None`	Passed
oracle 6	`{'format': 1, 'ppq': 480, 'tracks': 2}`	`None`	Failed
oracle 7	`None`	`None`	Passed

SHA-256 / 99aa7d7b221f6443852005a0395ea8d32d00a18ff52a0459896fe8d3d1115357

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) < 14 or x[:4] != [77, 84, 104, 100]:
        return None
    length = (x[4] << 24) | (x[5] << 16) | (x[6] << 8) | x[7]
    if length < 6 or len(x) < 8 + length:
        return None
    fmt = (x[8] << 8) | x[9]
    ntrks = (x[10] << 8) | x[11]
    division = (x[12] << 8) | x[13]
    if fmt not in (0, 1, 2) or ntrks == 0 or (fmt == 0 and ntrks != 1):
        return None
    if division & 0x8000:
        fps = 256 - x[12]
        if fps not in (24, 25, 29, 30):
            return None
        return {'format': fmt, 'tracks': ntrks, 'fps': fps, 'ticks_per_frame': x[13]}
    if division == 0:
        return None
    return {'format': fmt, 'tracks': ntrks, 'ppq': division}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 2, 1, 224], {'format': 1, 'tracks': 2, 'ppq': 480}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 0, 0, 2, 0, 96], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 3, 231, 40], {'format': 1, 'tracks': 3, 'fps': 25, 'ticks_per_frame': 40}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 230, 4], None), ([77, 84, 104, 100, 0, 0, 0, 8, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 5, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 1, 0, 6, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 3, 0, 2, 1, 224], None)], [([77, 84, 104, 100, 0, 0, 0, 6, 0, 0, 0, 1, 0, 96], {'format': 0, 'tracks': 1, 'ppq': 96}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 232, 80], {'format': 1, 'tracks': 1, 'fps': 24, 'ticks_per_frame': 80}), ([77, 84, 104, 100, 0, 0, 0, 5, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 1, 0, 6, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 3, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 0, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 2, 0, 0], None), ([77, 84, 105, 100, 0, 0, 0, 6, 0, 1, 0, 2, 1, 224], None)], [([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 2, 1, 224], {'format': 1, 'tracks': 2, 'ppq': 480}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 3, 231, 40], {'format': 1, 'tracks': 3, 'fps': 25, 'ticks_per_frame': 40}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 227, 4], {'format': 1, 'tracks': 1, 'fps': 29, 'ticks_per_frame': 4}), ([77, 84, 104, 100, 0, 1, 0, 6, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 2, 0, 0], None), ([77, 84, 105, 100, 0, 0, 0, 6, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 2, 128, 0], None)], [([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 2, 1, 224], {'format': 1, 'tracks': 2, 'ppq': 480}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 0, 0, 1, 0, 96], {'format': 0, 'tracks': 1, 'ppq': 96}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 3, 231, 40], {'format': 1, 'tracks': 3, 'fps': 25, 'ticks_per_frame': 40}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 232, 80], {'format': 1, 'tracks': 1, 'fps': 24, 'ticks_per_frame': 80}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 227, 4], {'format': 1, 'tracks': 1, 'fps': 29, 'ticks_per_frame': 4}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 226, 100], {'format': 1, 'tracks': 1, 'fps': 30, 'ticks_per_frame': 100}), ([77, 84, 104, 100, 0, 1, 0, 6, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 2, 128, 0], None)], [([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 3, 231, 40], {'format': 1, 'tracks': 3, 'fps': 25, 'ticks_per_frame': 40}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 232, 80], {'format': 1, 'tracks': 1, 'fps': 24, 'ticks_per_frame': 80}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 227, 4], {'format': 1, 'tracks': 1, 'fps': 29, 'ticks_per_frame': 4}), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 1, 0, 1, 226, 100], {'format': 1, 'tracks': 1, 'fps': 30, 'ticks_per_frame': 100}), ([77, 84, 104, 100, 0, 0, 0, 8, 0, 1, 0, 2, 1, 224, 0, 0], {'format': 1, 'tracks': 2, 'ppq': 480}), ([77, 84, 104, 100, 0, 1, 0, 6, 0, 1, 0, 2, 1, 224], None), ([77, 84, 104, 100, 0, 0, 0, 6, 0, 2, 0, 5, 0, 120], {'format': 2, 'tracks': 5, 'ppq': 120}), ([77, 84, 104, 100, 0, 0, 0, 7, 0, 1, 0, 2, 1, 224, 9], {'format': 1, 'tracks': 2, 'ppq': 480})]]
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	`{'format': 1, 'ppq': 480, 'tracks': 2}`	`{'format': 1, 'ppq': 480, 'tracks': 2}`	Passed
oracle 1	`None`	`None`	Passed
oracle 2	`{'format': 1, 'fps': 25, 'ticks_per_frame': 40, 'tracks': 3}`	`{'format': 1, 'fps': 25, 'ticks_per_frame': 40, 'tracks': 3}`	Passed
oracle 3	`None`	`None`	Passed
oracle 4	`None`	`None`	Passed
oracle 5	`None`	`None`	Passed
oracle 6	`None`	`None`	Passed
oracle 7	`None`	`None`	Passed

SHA-256 / 618265379f257e11de9b07f97d7133cbdc54bffe3771f5a37826680b7c3060e0

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 2026-09-29T14:50:02.491988+00:00.

Case digest / 48784af8a78c3e74879017a2ac331044f81d5abac69e44797fa1d8835d71dd79