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FA-81596 / MIDI event timing / Open access

MIDI clock transport and song position: start resumes from the old position · case 01

Start after playback resumes counting from the previous position instead of from 0.

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

ROOT CAUSE

The start handler sets the running flag but does not rewind.

VERIFIED REPAIR

Restore the start resets position step so that it reads `if kind == 'start': pos = 0 running = True`.

Unsuccessful approach: Rewinding without setting the running flag leaves the transport stopped after start.

Case contract

Input a list of messages: ["start"], ["continue"], ["stop"], ["clock"] or ["spp", lsb, msb]. start resets the position to 0 and runs; continue runs from the current position; stop halts; clock advances the position by one clock only while running; a song position pointer (in sixteenth notes, 6 clocks each, 14-bit lsb/msb) is honoured only while stopped. Return [position in clocks, running, quarter notes = position // 24]; unknown messages return 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):
        return None
    pos = 0
    running = False
    for msg in x:
        kind = msg[0]
        if kind == 'start':
            running = True
        elif kind == 'continue':
            running = True
        elif kind == 'stop':
            running = False
        elif kind == 'clock':
            if running:
                pos += 1
        elif kind == 'spp':
            if not running:
                pos = 6 * ((msg[2] << 7) | msg[1])
        else:
            return None
    return [pos, running, pos // 24]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[([['start'], ['clock'], ['clock']], [2, True, 0]), ([['clock'], ['clock']], [0, False, 0]), ([['spp', 4, 0], ['continue'], ['clock']], [25, True, 1]), ([['spp', 0, 1], ['continue']], [768, True, 32]), ([['spp', 1, 1]], [774, False, 32]), ([['start'], ['clock'], ['stop'], ['start'], ['clock']], [1, True, 0]), ([['stop'], ['spp', 3, 0], ['continue'], ['clock'], ['clock']], [20, True, 0]), ([['reset']], None)], [([['start'], ['clock'], ['stop'], ['clock'], ['continue'], ['clock']], [2, True, 0]), ([['spp', 1, 1]], [774, False, 32]), ([['spp', 16, 0], ['start']], [0, True, 0]), ([['stop'], ['spp', 3, 0], ['continue'], ['clock'], ['clock']], [20, True, 0]), ([['reset']], None), ([], [0, False, 0]), ([['spp', 127, 127]], [98298, False, 4095]), ([['spp', 4, 0], ['continue'], ['stop'], ['continue'], ['clock']], [25, True, 1])], [([['start'], ['spp', 8, 0], ['clock']], [1, True, 0]), ([['start'], ['clock'], ['stop'], ['start'], ['clock']], [1, True, 0]), ([], [0, False, 0]), ([['start'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock']], [25, True, 1]), ([['spp', 127, 127]], [98298, False, 4095]), ([['spp', 4, 0], ['continue'], ['stop'], ['continue'], ['clock']], [25, True, 1]), ([['start'], ['clock'], ['clock'], ['stop'], ['spp', 2, 0], ['continue'], ['clock']], [13, True, 0]), ([['continue'], ['clock']], [1, True, 0])], [([['start'], ['clock'], ['clock']], [2, True, 0]), ([['start'], ['clock'], ['stop'], ['clock'], ['continue'], ['clock']], [2, True, 0]), ([['start'], ['spp', 8, 0], ['clock']], [1, True, 0]), ([['start'], ['clock'], ['stop'], ['start'], ['clock']], [1, True, 0]), ([['spp', 16, 0], ['start']], [0, True, 0]), ([['start'], ['clock'], ['clock'], ['stop'], ['spp', 2, 0], ['continue'], ['clock']], [13, True, 0]), ([['continue'], ['clock']], [1, True, 0]), ([['start'], ['stop'], ['continue'], ['clock']], [1, True, 0])], [([['start'], ['clock'], ['clock']], [2, True, 0]), ([['clock'], ['clock']], [0, False, 0]), ([['start'], ['clock'], ['stop'], ['clock'], ['continue'], ['clock']], [2, True, 0]), ([['spp', 4, 0], ['continue'], ['clock']], [25, True, 1]), ([['start'], ['spp', 8, 0], ['clock']], [1, True, 0]), ([['start'], ['clock'], ['stop'], ['start'], ['clock']], [1, True, 0]), ([['spp', 16, 0], ['start']], [0, True, 0]), ([['start'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock']], [25, True, 1])]]
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 fixtureActualExpectedOutcome
oracle 0[2, True, 0][2, True, 0]Passed
oracle 1[0, False, 0][0, False, 0]Passed
oracle 2[25, True, 1][25, True, 1]Passed
oracle 3[768, True, 32][768, True, 32]Passed
oracle 4[774, False, 32][774, False, 32]Passed
oracle 5[2, True, 0][1, True, 0]Failed
oracle 6[20, True, 0][20, True, 0]Passed
oracle 7NoneNonePassed

SHA-256 / 894b54c70d3d40f126a1a80431dda1e73f867bd589685048b922b2e037877a85

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
    pos = 0
    running = False
    for msg in x:
        kind = msg[0]
        if kind == 'start':
            pos = 0
        elif kind == 'continue':
            running = True
        elif kind == 'stop':
            running = False
        elif kind == 'clock':
            if running:
                pos += 1
        elif kind == 'spp':
            if not running:
                pos = 6 * ((msg[2] << 7) | msg[1])
        else:
            return None
    return [pos, running, pos // 24]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[([['start'], ['clock'], ['clock']], [2, True, 0]), ([['clock'], ['clock']], [0, False, 0]), ([['spp', 4, 0], ['continue'], ['clock']], [25, True, 1]), ([['spp', 0, 1], ['continue']], [768, True, 32]), ([['spp', 1, 1]], [774, False, 32]), ([['start'], ['clock'], ['stop'], ['start'], ['clock']], [1, True, 0]), ([['stop'], ['spp', 3, 0], ['continue'], ['clock'], ['clock']], [20, True, 0]), ([['reset']], None)], [([['start'], ['clock'], ['stop'], ['clock'], ['continue'], ['clock']], [2, True, 0]), ([['spp', 1, 1]], [774, False, 32]), ([['spp', 16, 0], ['start']], [0, True, 0]), ([['stop'], ['spp', 3, 0], ['continue'], ['clock'], ['clock']], [20, True, 0]), ([['reset']], None), ([], [0, False, 0]), ([['spp', 127, 127]], [98298, False, 4095]), ([['spp', 4, 0], ['continue'], ['stop'], ['continue'], ['clock']], [25, True, 1])], [([['start'], ['spp', 8, 0], ['clock']], [1, True, 0]), ([['start'], ['clock'], ['stop'], ['start'], ['clock']], [1, True, 0]), ([], [0, False, 0]), ([['start'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock']], [25, True, 1]), ([['spp', 127, 127]], [98298, False, 4095]), ([['spp', 4, 0], ['continue'], ['stop'], ['continue'], ['clock']], [25, True, 1]), ([['start'], ['clock'], ['clock'], ['stop'], ['spp', 2, 0], ['continue'], ['clock']], [13, True, 0]), ([['continue'], ['clock']], [1, True, 0])], [([['start'], ['clock'], ['clock']], [2, True, 0]), ([['start'], ['clock'], ['stop'], ['clock'], ['continue'], ['clock']], [2, True, 0]), ([['start'], ['spp', 8, 0], ['clock']], [1, True, 0]), ([['start'], ['clock'], ['stop'], ['start'], ['clock']], [1, True, 0]), ([['spp', 16, 0], ['start']], [0, True, 0]), ([['start'], ['clock'], ['clock'], ['stop'], ['spp', 2, 0], ['continue'], ['clock']], [13, True, 0]), ([['continue'], ['clock']], [1, True, 0]), ([['start'], ['stop'], ['continue'], ['clock']], [1, True, 0])], [([['start'], ['clock'], ['clock']], [2, True, 0]), ([['clock'], ['clock']], [0, False, 0]), ([['start'], ['clock'], ['stop'], ['clock'], ['continue'], ['clock']], [2, True, 0]), ([['spp', 4, 0], ['continue'], ['clock']], [25, True, 1]), ([['start'], ['spp', 8, 0], ['clock']], [1, True, 0]), ([['start'], ['clock'], ['stop'], ['start'], ['clock']], [1, True, 0]), ([['spp', 16, 0], ['start']], [0, True, 0]), ([['start'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock']], [25, True, 1])]]
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 fixtureActualExpectedOutcome
oracle 0[0, False, 0][2, True, 0]Failed
oracle 1[0, False, 0][0, False, 0]Passed
oracle 2[25, True, 1][25, True, 1]Passed
oracle 3[768, True, 32][768, True, 32]Passed
oracle 4[774, False, 32][774, False, 32]Passed
oracle 5[0, False, 0][1, True, 0]Failed
oracle 6[20, True, 0][20, True, 0]Passed
oracle 7NoneNonePassed

SHA-256 / f145b2e2414b4ec6e4a748903c86e63262a8dd9c19c3ad5ef09d07bdab226de3

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
    pos = 0
    running = False
    for msg in x:
        kind = msg[0]
        if kind == 'start':
            pos = 0
            running = True
        elif kind == 'continue':
            running = True
        elif kind == 'stop':
            running = False
        elif kind == 'clock':
            if running:
                pos += 1
        elif kind == 'spp':
            if not running:
                pos = 6 * ((msg[2] << 7) | msg[1])
        else:
            return None
    return [pos, running, pos // 24]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[([['start'], ['clock'], ['clock']], [2, True, 0]), ([['clock'], ['clock']], [0, False, 0]), ([['spp', 4, 0], ['continue'], ['clock']], [25, True, 1]), ([['spp', 0, 1], ['continue']], [768, True, 32]), ([['spp', 1, 1]], [774, False, 32]), ([['start'], ['clock'], ['stop'], ['start'], ['clock']], [1, True, 0]), ([['stop'], ['spp', 3, 0], ['continue'], ['clock'], ['clock']], [20, True, 0]), ([['reset']], None)], [([['start'], ['clock'], ['stop'], ['clock'], ['continue'], ['clock']], [2, True, 0]), ([['spp', 1, 1]], [774, False, 32]), ([['spp', 16, 0], ['start']], [0, True, 0]), ([['stop'], ['spp', 3, 0], ['continue'], ['clock'], ['clock']], [20, True, 0]), ([['reset']], None), ([], [0, False, 0]), ([['spp', 127, 127]], [98298, False, 4095]), ([['spp', 4, 0], ['continue'], ['stop'], ['continue'], ['clock']], [25, True, 1])], [([['start'], ['spp', 8, 0], ['clock']], [1, True, 0]), ([['start'], ['clock'], ['stop'], ['start'], ['clock']], [1, True, 0]), ([], [0, False, 0]), ([['start'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock']], [25, True, 1]), ([['spp', 127, 127]], [98298, False, 4095]), ([['spp', 4, 0], ['continue'], ['stop'], ['continue'], ['clock']], [25, True, 1]), ([['start'], ['clock'], ['clock'], ['stop'], ['spp', 2, 0], ['continue'], ['clock']], [13, True, 0]), ([['continue'], ['clock']], [1, True, 0])], [([['start'], ['clock'], ['clock']], [2, True, 0]), ([['start'], ['clock'], ['stop'], ['clock'], ['continue'], ['clock']], [2, True, 0]), ([['start'], ['spp', 8, 0], ['clock']], [1, True, 0]), ([['start'], ['clock'], ['stop'], ['start'], ['clock']], [1, True, 0]), ([['spp', 16, 0], ['start']], [0, True, 0]), ([['start'], ['clock'], ['clock'], ['stop'], ['spp', 2, 0], ['continue'], ['clock']], [13, True, 0]), ([['continue'], ['clock']], [1, True, 0]), ([['start'], ['stop'], ['continue'], ['clock']], [1, True, 0])], [([['start'], ['clock'], ['clock']], [2, True, 0]), ([['clock'], ['clock']], [0, False, 0]), ([['start'], ['clock'], ['stop'], ['clock'], ['continue'], ['clock']], [2, True, 0]), ([['spp', 4, 0], ['continue'], ['clock']], [25, True, 1]), ([['start'], ['spp', 8, 0], ['clock']], [1, True, 0]), ([['start'], ['clock'], ['stop'], ['start'], ['clock']], [1, True, 0]), ([['spp', 16, 0], ['start']], [0, True, 0]), ([['start'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock'], ['clock']], [25, True, 1])]]
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 fixtureActualExpectedOutcome
oracle 0[2, True, 0][2, True, 0]Passed
oracle 1[0, False, 0][0, False, 0]Passed
oracle 2[25, True, 1][25, True, 1]Passed
oracle 3[768, True, 32][768, True, 32]Passed
oracle 4[774, False, 32][774, False, 32]Passed
oracle 5[1, True, 0][1, True, 0]Passed
oracle 6[20, True, 0][20, True, 0]Passed
oracle 7NoneNonePassed

SHA-256 / 6063e841c7c27816661af5adebd840d3640a0ab300213f95f6dee7388051d336

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 2026-09-29T14:50:04.438126+00:00.

Case digest / 543425bbfb176d47414b53196fa6e4a94e982b507f25a9d642e76f4b032705a4