FA-81426 / MIDI event timing / Open access

Track event parser with running status: deltas treated as absolute times · case 01

Event times reset after each event: the second of two events 10 ticks apart reports tick 10 regardless of history.

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

ROOT CAUSE

Each event tick is set to its own delta instead of adding the delta to the running time.

VERIFIED REPAIR

Restore the delta accumulation step so that it reads `tick += delta`.

Unsuccessful approach: Taking the maximum of the running tick and the delta still ignores accumulated time for small deltas.

Case contract

Input the bytes of a track body: each event is a variable-length delta then either a meta event (FF type len data...), a status byte (bit 7 set) with its data bytes, or data bytes reusing the previous channel status (running status). Program change (Cx) and channel pressure (Dx) take one data byte, other channel messages two. Meta events cancel running status. Return [absolute tick, status, data...] for channel events and [tick, "meta", type] for meta events, or None on truncation or data without a running status.

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):
        return None
    out = []
    i = 0
    tick = 0
    running = None
    while i < len(x):
        delta = 0
        while True:
            if i >= len(x):
                return None
            b = x[i]
            i += 1
            delta = (delta << 7) | (b & 0x7F)
            if not b & 0x80:
                break
        tick = delta
        if i >= len(x):
            return None
        status = x[i]
        if status == 0xFF:
            if i + 2 >= len(x):
                return None
            kind = x[i + 1]
            i += 3 + x[i + 2]
            if i > len(x):
                return None
            running = None
            out.append([tick, 'meta', kind])
            continue
        if status & 0x80:
            i += 1
            running = status
        elif running is None:
            return None
        else:
            status = running
        size = 1 if (status & 0xF0) in (0xC0, 0xD0) else 2
        if i + size > len(x):
            return None
        out.append([tick, status] + x[i:i + size])
        i += size
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[([0, 144, 60, 100, 10, 60, 0], [[0, 144, 60, 100], [10, 144, 60, 0]]), ([0, 192, 5, 0, 6], [[0, 192, 5], [0, 192, 6]]), ([0, 208, 64, 0, 50], [[0, 208, 64], [0, 208, 50]]), ([0, 144, 60, 100, 0, 255, 1, 0, 0, 62, 100], None), ([0, 144, 60, 100, 0, 255, 1, 1, 65, 0, 62, 100], None), ([0, 176, 7, 100, 20, 10, 90], [[0, 176, 7, 100], [20, 176, 10, 90]]), ([0, 192, 5, 7, 6, 0, 144, 64, 90], [[0, 192, 5], [7, 192, 6], [7, 144, 64, 90]]), ([5, 144, 60, 100, 5, 128, 60, 0, 5, 62, 0], [[5, 144, 60, 100], [10, 128, 60, 0], [15, 128, 62, 0]])], [([0, 144, 60, 100, 0, 255, 1, 0, 0, 62, 100], None), ([0, 144, 60, 100, 0, 255, 1, 1, 65, 0, 62, 100], None), ([0, 176, 7, 100, 20, 10, 90], [[0, 176, 7, 100], [20, 176, 10, 90]]), ([127, 144, 60, 1], [[127, 144, 60, 1]]), ([128, 0, 144, 60, 1], [[0, 144, 60, 1]]), ([129, 0, 144, 60, 1], [[128, 144, 60, 1]]), ([0, 144, 60], None), ([5, 144, 60, 100, 5, 128, 60, 0, 5, 62, 0], [[5, 144, 60, 100], [10, 128, 60, 0], [15, 128, 62, 0]])], [([127, 144, 60, 1], [[127, 144, 60, 1]]), ([128, 0, 144, 60, 1], [[0, 144, 60, 1]]), ([129, 0, 144, 60, 1], [[128, 144, 60, 1]]), ([0, 144, 60], None), ([0, 62, 100], None), ([0, 192, 5, 7, 6, 0, 144, 64, 90], [[0, 192, 5], [7, 192, 6], [7, 144, 64, 90]]), ([0, 255, 47, 0], [[0, 'meta', 47]]), ([5, 144, 60, 100, 5, 128, 60, 0, 5, 62, 0], [[5, 144, 60, 100], [10, 128, 60, 0], [15, 128, 62, 0]])], [([0, 144, 60], None), ([0, 62, 100], None), ([0, 255, 47, 0], [[0, 'meta', 47]]), ([0, 255, 81, 3, 7, 161, 32, 0, 144, 60, 64], [[0, 'meta', 81], [0, 144, 60, 64]]), ([0, 224, 0, 64, 16, 0, 65], [[0, 224, 0, 64], [16, 224, 0, 65]]), ([5, 144, 60, 100, 5, 128, 60, 0, 5, 62, 0], [[5, 144, 60, 100], [10, 128, 60, 0], [15, 128, 62, 0]]), ([0, 208, 10, 0, 20], [[0, 208, 10], [0, 208, 20]]), ([0, 255, 3], None)], [([0, 192, 5, 7, 6, 0, 144, 64, 90], [[0, 192, 5], [7, 192, 6], [7, 144, 64, 90]]), ([0, 255, 81, 3, 7, 161, 32, 0, 144, 60, 64], [[0, 'meta', 81], [0, 144, 60, 64]]), ([0, 224, 0, 64, 16, 0, 65], [[0, 224, 0, 64], [16, 224, 0, 65]]), ([5, 144, 60, 100, 5, 128, 60, 0, 5, 62, 0], [[5, 144, 60, 100], [10, 128, 60, 0], [15, 128, 62, 0]]), ([0, 208, 10, 0, 20], [[0, 208, 10], [0, 208, 20]]), ([0, 255, 3], None), ([0, 255, 3, 5, 65], None), ([0, 144, 60, 100, 0, 192, 9, 3, 11], [[0, 144, 60, 100], [0, 192, 9], [3, 192, 11]])]]
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, 144, 60, 100], [10, 144, 60, 0]]`	`[[0, 144, 60, 100], [10, 144, 60, 0]]`	Passed
oracle 1	`[[0, 192, 5], [0, 192, 6]]`	`[[0, 192, 5], [0, 192, 6]]`	Passed
oracle 2	`[[0, 208, 64], [0, 208, 50]]`	`[[0, 208, 64], [0, 208, 50]]`	Passed
oracle 3	`None`	`None`	Passed
oracle 4	`None`	`None`	Passed
oracle 5	`[[0, 176, 7, 100], [20, 176, 10, 90]]`	`[[0, 176, 7, 100], [20, 176, 10, 90]]`	Passed
oracle 6	`[[0, 192, 5], [7, 192, 6], [0, 144, 64, 90]]`	`[[0, 192, 5], [7, 192, 6], [7, 144, 64, 90]]`	Failed
oracle 7	`[[5, 144, 60, 100], [5, 128, 60, 0], [5, 128, 62, 0]]`	`[[5, 144, 60, 100], [10, 128, 60, 0], [15, 128, 62, 0]]`	Failed

SHA-256 / c11e395636a884f8475e15801a7fdea16b8523728b4d437bd433d83670c71f62

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):
        return None
    out = []
    i = 0
    tick = 0
    running = None
    while i < len(x):
        delta = 0
        while True:
            if i >= len(x):
                return None
            b = x[i]
            i += 1
            delta = (delta << 7) | (b & 0x7F)
            if not b & 0x80:
                break
        tick = max(tick, delta)
        if i >= len(x):
            return None
        status = x[i]
        if status == 0xFF:
            if i + 2 >= len(x):
                return None
            kind = x[i + 1]
            i += 3 + x[i + 2]
            if i > len(x):
                return None
            running = None
            out.append([tick, 'meta', kind])
            continue
        if status & 0x80:
            i += 1
            running = status
        elif running is None:
            return None
        else:
            status = running
        size = 1 if (status & 0xF0) in (0xC0, 0xD0) else 2
        if i + size > len(x):
            return None
        out.append([tick, status] + x[i:i + size])
        i += size
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[([0, 144, 60, 100, 10, 60, 0], [[0, 144, 60, 100], [10, 144, 60, 0]]), ([0, 192, 5, 0, 6], [[0, 192, 5], [0, 192, 6]]), ([0, 208, 64, 0, 50], [[0, 208, 64], [0, 208, 50]]), ([0, 144, 60, 100, 0, 255, 1, 0, 0, 62, 100], None), ([0, 144, 60, 100, 0, 255, 1, 1, 65, 0, 62, 100], None), ([0, 176, 7, 100, 20, 10, 90], [[0, 176, 7, 100], [20, 176, 10, 90]]), ([0, 192, 5, 7, 6, 0, 144, 64, 90], [[0, 192, 5], [7, 192, 6], [7, 144, 64, 90]]), ([5, 144, 60, 100, 5, 128, 60, 0, 5, 62, 0], [[5, 144, 60, 100], [10, 128, 60, 0], [15, 128, 62, 0]])], [([0, 144, 60, 100, 0, 255, 1, 0, 0, 62, 100], None), ([0, 144, 60, 100, 0, 255, 1, 1, 65, 0, 62, 100], None), ([0, 176, 7, 100, 20, 10, 90], [[0, 176, 7, 100], [20, 176, 10, 90]]), ([127, 144, 60, 1], [[127, 144, 60, 1]]), ([128, 0, 144, 60, 1], [[0, 144, 60, 1]]), ([129, 0, 144, 60, 1], [[128, 144, 60, 1]]), ([0, 144, 60], None), ([5, 144, 60, 100, 5, 128, 60, 0, 5, 62, 0], [[5, 144, 60, 100], [10, 128, 60, 0], [15, 128, 62, 0]])], [([127, 144, 60, 1], [[127, 144, 60, 1]]), ([128, 0, 144, 60, 1], [[0, 144, 60, 1]]), ([129, 0, 144, 60, 1], [[128, 144, 60, 1]]), ([0, 144, 60], None), ([0, 62, 100], None), ([0, 192, 5, 7, 6, 0, 144, 64, 90], [[0, 192, 5], [7, 192, 6], [7, 144, 64, 90]]), ([0, 255, 47, 0], [[0, 'meta', 47]]), ([5, 144, 60, 100, 5, 128, 60, 0, 5, 62, 0], [[5, 144, 60, 100], [10, 128, 60, 0], [15, 128, 62, 0]])], [([0, 144, 60], None), ([0, 62, 100], None), ([0, 255, 47, 0], [[0, 'meta', 47]]), ([0, 255, 81, 3, 7, 161, 32, 0, 144, 60, 64], [[0, 'meta', 81], [0, 144, 60, 64]]), ([0, 224, 0, 64, 16, 0, 65], [[0, 224, 0, 64], [16, 224, 0, 65]]), ([5, 144, 60, 100, 5, 128, 60, 0, 5, 62, 0], [[5, 144, 60, 100], [10, 128, 60, 0], [15, 128, 62, 0]]), ([0, 208, 10, 0, 20], [[0, 208, 10], [0, 208, 20]]), ([0, 255, 3], None)], [([0, 192, 5, 7, 6, 0, 144, 64, 90], [[0, 192, 5], [7, 192, 6], [7, 144, 64, 90]]), ([0, 255, 81, 3, 7, 161, 32, 0, 144, 60, 64], [[0, 'meta', 81], [0, 144, 60, 64]]), ([0, 224, 0, 64, 16, 0, 65], [[0, 224, 0, 64], [16, 224, 0, 65]]), ([5, 144, 60, 100, 5, 128, 60, 0, 5, 62, 0], [[5, 144, 60, 100], [10, 128, 60, 0], [15, 128, 62, 0]]), ([0, 208, 10, 0, 20], [[0, 208, 10], [0, 208, 20]]), ([0, 255, 3], None), ([0, 255, 3, 5, 65], None), ([0, 144, 60, 100, 0, 192, 9, 3, 11], [[0, 144, 60, 100], [0, 192, 9], [3, 192, 11]])]]
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, 144, 60, 100], [10, 144, 60, 0]]`	`[[0, 144, 60, 100], [10, 144, 60, 0]]`	Passed
oracle 1	`[[0, 192, 5], [0, 192, 6]]`	`[[0, 192, 5], [0, 192, 6]]`	Passed
oracle 2	`[[0, 208, 64], [0, 208, 50]]`	`[[0, 208, 64], [0, 208, 50]]`	Passed
oracle 3	`None`	`None`	Passed
oracle 4	`None`	`None`	Passed
oracle 5	`[[0, 176, 7, 100], [20, 176, 10, 90]]`	`[[0, 176, 7, 100], [20, 176, 10, 90]]`	Passed
oracle 6	`[[0, 192, 5], [7, 192, 6], [7, 144, 64, 90]]`	`[[0, 192, 5], [7, 192, 6], [7, 144, 64, 90]]`	Passed
oracle 7	`[[5, 144, 60, 100], [5, 128, 60, 0], [5, 128, 62, 0]]`	`[[5, 144, 60, 100], [10, 128, 60, 0], [15, 128, 62, 0]]`	Failed

SHA-256 / d8ebbed184461f89c756354a9e9b5ad7cea429a141c2c806a5c50780c711055b

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):
        return None
    out = []
    i = 0
    tick = 0
    running = None
    while i < len(x):
        delta = 0
        while True:
            if i >= len(x):
                return None
            b = x[i]
            i += 1
            delta = (delta << 7) | (b & 0x7F)
            if not b & 0x80:
                break
        tick += delta
        if i >= len(x):
            return None
        status = x[i]
        if status == 0xFF:
            if i + 2 >= len(x):
                return None
            kind = x[i + 1]
            i += 3 + x[i + 2]
            if i > len(x):
                return None
            running = None
            out.append([tick, 'meta', kind])
            continue
        if status & 0x80:
            i += 1
            running = status
        elif running is None:
            return None
        else:
            status = running
        size = 1 if (status & 0xF0) in (0xC0, 0xD0) else 2
        if i + size > len(x):
            return None
        out.append([tick, status] + x[i:i + size])
        i += size
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[([0, 144, 60, 100, 10, 60, 0], [[0, 144, 60, 100], [10, 144, 60, 0]]), ([0, 192, 5, 0, 6], [[0, 192, 5], [0, 192, 6]]), ([0, 208, 64, 0, 50], [[0, 208, 64], [0, 208, 50]]), ([0, 144, 60, 100, 0, 255, 1, 0, 0, 62, 100], None), ([0, 144, 60, 100, 0, 255, 1, 1, 65, 0, 62, 100], None), ([0, 176, 7, 100, 20, 10, 90], [[0, 176, 7, 100], [20, 176, 10, 90]]), ([0, 192, 5, 7, 6, 0, 144, 64, 90], [[0, 192, 5], [7, 192, 6], [7, 144, 64, 90]]), ([5, 144, 60, 100, 5, 128, 60, 0, 5, 62, 0], [[5, 144, 60, 100], [10, 128, 60, 0], [15, 128, 62, 0]])], [([0, 144, 60, 100, 0, 255, 1, 0, 0, 62, 100], None), ([0, 144, 60, 100, 0, 255, 1, 1, 65, 0, 62, 100], None), ([0, 176, 7, 100, 20, 10, 90], [[0, 176, 7, 100], [20, 176, 10, 90]]), ([127, 144, 60, 1], [[127, 144, 60, 1]]), ([128, 0, 144, 60, 1], [[0, 144, 60, 1]]), ([129, 0, 144, 60, 1], [[128, 144, 60, 1]]), ([0, 144, 60], None), ([5, 144, 60, 100, 5, 128, 60, 0, 5, 62, 0], [[5, 144, 60, 100], [10, 128, 60, 0], [15, 128, 62, 0]])], [([127, 144, 60, 1], [[127, 144, 60, 1]]), ([128, 0, 144, 60, 1], [[0, 144, 60, 1]]), ([129, 0, 144, 60, 1], [[128, 144, 60, 1]]), ([0, 144, 60], None), ([0, 62, 100], None), ([0, 192, 5, 7, 6, 0, 144, 64, 90], [[0, 192, 5], [7, 192, 6], [7, 144, 64, 90]]), ([0, 255, 47, 0], [[0, 'meta', 47]]), ([5, 144, 60, 100, 5, 128, 60, 0, 5, 62, 0], [[5, 144, 60, 100], [10, 128, 60, 0], [15, 128, 62, 0]])], [([0, 144, 60], None), ([0, 62, 100], None), ([0, 255, 47, 0], [[0, 'meta', 47]]), ([0, 255, 81, 3, 7, 161, 32, 0, 144, 60, 64], [[0, 'meta', 81], [0, 144, 60, 64]]), ([0, 224, 0, 64, 16, 0, 65], [[0, 224, 0, 64], [16, 224, 0, 65]]), ([5, 144, 60, 100, 5, 128, 60, 0, 5, 62, 0], [[5, 144, 60, 100], [10, 128, 60, 0], [15, 128, 62, 0]]), ([0, 208, 10, 0, 20], [[0, 208, 10], [0, 208, 20]]), ([0, 255, 3], None)], [([0, 192, 5, 7, 6, 0, 144, 64, 90], [[0, 192, 5], [7, 192, 6], [7, 144, 64, 90]]), ([0, 255, 81, 3, 7, 161, 32, 0, 144, 60, 64], [[0, 'meta', 81], [0, 144, 60, 64]]), ([0, 224, 0, 64, 16, 0, 65], [[0, 224, 0, 64], [16, 224, 0, 65]]), ([5, 144, 60, 100, 5, 128, 60, 0, 5, 62, 0], [[5, 144, 60, 100], [10, 128, 60, 0], [15, 128, 62, 0]]), ([0, 208, 10, 0, 20], [[0, 208, 10], [0, 208, 20]]), ([0, 255, 3], None), ([0, 255, 3, 5, 65], None), ([0, 144, 60, 100, 0, 192, 9, 3, 11], [[0, 144, 60, 100], [0, 192, 9], [3, 192, 11]])]]
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, 144, 60, 100], [10, 144, 60, 0]]`	`[[0, 144, 60, 100], [10, 144, 60, 0]]`	Passed
oracle 1	`[[0, 192, 5], [0, 192, 6]]`	`[[0, 192, 5], [0, 192, 6]]`	Passed
oracle 2	`[[0, 208, 64], [0, 208, 50]]`	`[[0, 208, 64], [0, 208, 50]]`	Passed
oracle 3	`None`	`None`	Passed
oracle 4	`None`	`None`	Passed
oracle 5	`[[0, 176, 7, 100], [20, 176, 10, 90]]`	`[[0, 176, 7, 100], [20, 176, 10, 90]]`	Passed
oracle 6	`[[0, 192, 5], [7, 192, 6], [7, 144, 64, 90]]`	`[[0, 192, 5], [7, 192, 6], [7, 144, 64, 90]]`	Passed
oracle 7	`[[5, 144, 60, 100], [10, 128, 60, 0], [15, 128, 62, 0]]`	`[[5, 144, 60, 100], [10, 128, 60, 0], [15, 128, 62, 0]]`	Passed

SHA-256 / 4e01736750ac17c5c378a2119ae520a62703434d083bb737c19d3fac08824435

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 2026-09-29T14:50:03.013376+00:00.

Case digest / f382a221a5c4137a2391b651983020cc66632b2103abdbd05e44932b3f42aa81