FA-81781 / MIDI event timing / Open access

Channel note message encoder with running status: running-status note-off carries a release velocity · case 01

With running status on, a note-off with release velocity 40 is sent as a note-on with velocity 40, retriggering the note.

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

ROOT CAUSE

The note-on-as-note-off form copies the release velocity instead of sending velocity 0.

VERIFIED REPAIR

Restore the running-status note-off velocity step so that it reads `[note, 0]`.

Unsuccessful approach: Sending a fixed 64 is still a nonzero note-on velocity and retriggers the note.

Case contract

Input [events, running_status] with events [kind, channel 1..16, note, velocity]. A note-on with velocity > 0 encodes as 0x90|(channel-1), note, velocity. A note-off (or note-on with velocity 0) encodes as 0x90|(channel-1), note, 0 when running status is enabled; otherwise as 0x80|(channel-1), note, velocity for an off and note, 64 for a velocity-0 on. With running status enabled, a status byte equal to the previous one is omitted. Invalid values 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) or len(x) != 2:
        return None
    events, rs = x
    out = []
    last = None
    for kind, ch, note, vel in events:
        if not 1 <= ch <= 16 or not 0 <= note <= 127 or not 0 <= vel <= 127:
            return None
        if kind == 'on' and vel > 0:
            status, data = 0x90 | (ch - 1), [note, vel]
        elif kind in ('on', 'off'):
            if rs:
                status, data = 0x90 | (ch - 1), [note, vel]
            else:
                status, data = 0x80 | (ch - 1), [note, vel if kind == 'off' else 64]
        else:
            return None
        if not (rs and status == last):
            out.append(status)
        out.extend(data)
        last = status
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[([[['on', 1, 60, 100], ['off', 1, 60, 40]], False], [144, 60, 100, 128, 60, 40]), ([[['on', 1, 60, 100], ['off', 1, 60, 40]], True], [144, 60, 100, 60, 0]), ([[['on', 1, 60, 100], ['on', 1, 64, 90]], True], [144, 60, 100, 64, 90]), ([[['on', 1, 60, 100], ['on', 1, 64, 90]], False], [144, 60, 100, 144, 64, 90]), ([[['on', 16, 60, 100]], False], [159, 60, 100]), ([[['on', 0, 60, 100]], False], None), ([[['on', 17, 60, 100]], False], None), ([[['off', 5, 70, 90], ['off', 5, 71, 90]], True], [148, 70, 0, 71, 0])], [([[['on', 1, 60, 100], ['off', 1, 60, 40]], True], [144, 60, 100, 60, 0]), ([[['on', 16, 60, 100]], False], [159, 60, 100]), ([[['on', 0, 60, 100]], False], None), ([[['on', 17, 60, 100]], False], None), ([[['on', 2, 60, 0]], False], [129, 60, 64]), ([[['on', 2, 60, 0]], True], [145, 60, 0]), ([[['off', 3, 60, 0]], False], [130, 60, 0]), ([[['off', 5, 70, 90], ['off', 5, 71, 90]], True], [148, 70, 0, 71, 0])], [([[['on', 1, 60, 100], ['off', 1, 60, 40]], True], [144, 60, 100, 60, 0]), ([[['on', 2, 60, 0]], False], [129, 60, 64]), ([[['on', 2, 60, 0]], True], [145, 60, 0]), ([[['off', 3, 60, 0]], False], [130, 60, 0]), ([[['on', 1, 60, 100], ['on', 2, 60, 100]], True], [144, 60, 100, 145, 60, 100]), ([[['on', 1, 128, 100]], False], None), ([[['cc', 1, 7, 100]], False], None), ([[['on', 10, 36, 127], ['off', 10, 36, 0], ['on', 10, 38, 127]], True], [153, 36, 127, 36, 0, 38, 127])], [([[['on', 1, 60, 100], ['off', 1, 60, 40]], False], [144, 60, 100, 128, 60, 40]), ([[['on', 1, 60, 100], ['off', 1, 60, 40]], True], [144, 60, 100, 60, 0]), ([[['on', 2, 60, 0]], True], [145, 60, 0]), ([[['on', 1, 128, 100]], False], None), ([[['cc', 1, 7, 100]], False], None), ([[['on', 10, 36, 127], ['off', 10, 36, 0], ['on', 10, 38, 127]], True], [153, 36, 127, 36, 0, 38, 127]), ([[['on', 1, 60, 1]], True], [144, 60, 1]), ([[['off', 5, 70, 90], ['off', 5, 71, 90]], True], [148, 70, 0, 71, 0])], [([[['on', 1, 60, 100], ['off', 1, 60, 40]], False], [144, 60, 100, 128, 60, 40]), ([[['on', 1, 60, 100], ['off', 1, 60, 40]], True], [144, 60, 100, 60, 0]), ([[['on', 1, 60, 100], ['on', 1, 64, 90]], True], [144, 60, 100, 64, 90]), ([[['on', 1, 60, 100], ['on', 1, 64, 90]], False], [144, 60, 100, 144, 64, 90]), ([[['on', 16, 60, 100]], False], [159, 60, 100]), ([[['on', 2, 60, 0]], True], [145, 60, 0]), ([[['on', 10, 36, 127], ['off', 10, 36, 0], ['on', 10, 38, 127]], True], [153, 36, 127, 36, 0, 38, 127]), ([[['off', 5, 70, 90], ['off', 5, 71, 90]], True], [148, 70, 0, 71, 0])]]
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	`[144, 60, 100, 128, 60, 40]`	`[144, 60, 100, 128, 60, 40]`	Passed
oracle 1	`[144, 60, 100, 60, 40]`	`[144, 60, 100, 60, 0]`	Failed
oracle 2	`[144, 60, 100, 64, 90]`	`[144, 60, 100, 64, 90]`	Passed
oracle 3	`[144, 60, 100, 144, 64, 90]`	`[144, 60, 100, 144, 64, 90]`	Passed
oracle 4	`[159, 60, 100]`	`[159, 60, 100]`	Passed
oracle 5	`None`	`None`	Passed
oracle 6	`None`	`None`	Passed
oracle 7	`[148, 70, 90, 71, 90]`	`[148, 70, 0, 71, 0]`	Failed

SHA-256 / 502b705909ffdf00c08373ae4296507d3fb6e2afecb0bd11a0efc39a045ce120

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) != 2:
        return None
    events, rs = x
    out = []
    last = None
    for kind, ch, note, vel in events:
        if not 1 <= ch <= 16 or not 0 <= note <= 127 or not 0 <= vel <= 127:
            return None
        if kind == 'on' and vel > 0:
            status, data = 0x90 | (ch - 1), [note, vel]
        elif kind in ('on', 'off'):
            if rs:
                status, data = 0x90 | (ch - 1), [note, 64]
            else:
                status, data = 0x80 | (ch - 1), [note, vel if kind == 'off' else 64]
        else:
            return None
        if not (rs and status == last):
            out.append(status)
        out.extend(data)
        last = status
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[([[['on', 1, 60, 100], ['off', 1, 60, 40]], False], [144, 60, 100, 128, 60, 40]), ([[['on', 1, 60, 100], ['off', 1, 60, 40]], True], [144, 60, 100, 60, 0]), ([[['on', 1, 60, 100], ['on', 1, 64, 90]], True], [144, 60, 100, 64, 90]), ([[['on', 1, 60, 100], ['on', 1, 64, 90]], False], [144, 60, 100, 144, 64, 90]), ([[['on', 16, 60, 100]], False], [159, 60, 100]), ([[['on', 0, 60, 100]], False], None), ([[['on', 17, 60, 100]], False], None), ([[['off', 5, 70, 90], ['off', 5, 71, 90]], True], [148, 70, 0, 71, 0])], [([[['on', 1, 60, 100], ['off', 1, 60, 40]], True], [144, 60, 100, 60, 0]), ([[['on', 16, 60, 100]], False], [159, 60, 100]), ([[['on', 0, 60, 100]], False], None), ([[['on', 17, 60, 100]], False], None), ([[['on', 2, 60, 0]], False], [129, 60, 64]), ([[['on', 2, 60, 0]], True], [145, 60, 0]), ([[['off', 3, 60, 0]], False], [130, 60, 0]), ([[['off', 5, 70, 90], ['off', 5, 71, 90]], True], [148, 70, 0, 71, 0])], [([[['on', 1, 60, 100], ['off', 1, 60, 40]], True], [144, 60, 100, 60, 0]), ([[['on', 2, 60, 0]], False], [129, 60, 64]), ([[['on', 2, 60, 0]], True], [145, 60, 0]), ([[['off', 3, 60, 0]], False], [130, 60, 0]), ([[['on', 1, 60, 100], ['on', 2, 60, 100]], True], [144, 60, 100, 145, 60, 100]), ([[['on', 1, 128, 100]], False], None), ([[['cc', 1, 7, 100]], False], None), ([[['on', 10, 36, 127], ['off', 10, 36, 0], ['on', 10, 38, 127]], True], [153, 36, 127, 36, 0, 38, 127])], [([[['on', 1, 60, 100], ['off', 1, 60, 40]], False], [144, 60, 100, 128, 60, 40]), ([[['on', 1, 60, 100], ['off', 1, 60, 40]], True], [144, 60, 100, 60, 0]), ([[['on', 2, 60, 0]], True], [145, 60, 0]), ([[['on', 1, 128, 100]], False], None), ([[['cc', 1, 7, 100]], False], None), ([[['on', 10, 36, 127], ['off', 10, 36, 0], ['on', 10, 38, 127]], True], [153, 36, 127, 36, 0, 38, 127]), ([[['on', 1, 60, 1]], True], [144, 60, 1]), ([[['off', 5, 70, 90], ['off', 5, 71, 90]], True], [148, 70, 0, 71, 0])], [([[['on', 1, 60, 100], ['off', 1, 60, 40]], False], [144, 60, 100, 128, 60, 40]), ([[['on', 1, 60, 100], ['off', 1, 60, 40]], True], [144, 60, 100, 60, 0]), ([[['on', 1, 60, 100], ['on', 1, 64, 90]], True], [144, 60, 100, 64, 90]), ([[['on', 1, 60, 100], ['on', 1, 64, 90]], False], [144, 60, 100, 144, 64, 90]), ([[['on', 16, 60, 100]], False], [159, 60, 100]), ([[['on', 2, 60, 0]], True], [145, 60, 0]), ([[['on', 10, 36, 127], ['off', 10, 36, 0], ['on', 10, 38, 127]], True], [153, 36, 127, 36, 0, 38, 127]), ([[['off', 5, 70, 90], ['off', 5, 71, 90]], True], [148, 70, 0, 71, 0])]]
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	`[144, 60, 100, 128, 60, 40]`	`[144, 60, 100, 128, 60, 40]`	Passed
oracle 1	`[144, 60, 100, 60, 64]`	`[144, 60, 100, 60, 0]`	Failed
oracle 2	`[144, 60, 100, 64, 90]`	`[144, 60, 100, 64, 90]`	Passed
oracle 3	`[144, 60, 100, 144, 64, 90]`	`[144, 60, 100, 144, 64, 90]`	Passed
oracle 4	`[159, 60, 100]`	`[159, 60, 100]`	Passed
oracle 5	`None`	`None`	Passed
oracle 6	`None`	`None`	Passed
oracle 7	`[148, 70, 64, 71, 64]`	`[148, 70, 0, 71, 0]`	Failed

SHA-256 / 1ac6f709c490969faaa6399b856243f383e570b9104e460ddd55c8f6191c1386

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) != 2:
        return None
    events, rs = x
    out = []
    last = None
    for kind, ch, note, vel in events:
        if not 1 <= ch <= 16 or not 0 <= note <= 127 or not 0 <= vel <= 127:
            return None
        if kind == 'on' and vel > 0:
            status, data = 0x90 | (ch - 1), [note, vel]
        elif kind in ('on', 'off'):
            if rs:
                status, data = 0x90 | (ch - 1), [note, 0]
            else:
                status, data = 0x80 | (ch - 1), [note, vel if kind == 'off' else 64]
        else:
            return None
        if not (rs and status == last):
            out.append(status)
        out.extend(data)
        last = status
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[([[['on', 1, 60, 100], ['off', 1, 60, 40]], False], [144, 60, 100, 128, 60, 40]), ([[['on', 1, 60, 100], ['off', 1, 60, 40]], True], [144, 60, 100, 60, 0]), ([[['on', 1, 60, 100], ['on', 1, 64, 90]], True], [144, 60, 100, 64, 90]), ([[['on', 1, 60, 100], ['on', 1, 64, 90]], False], [144, 60, 100, 144, 64, 90]), ([[['on', 16, 60, 100]], False], [159, 60, 100]), ([[['on', 0, 60, 100]], False], None), ([[['on', 17, 60, 100]], False], None), ([[['off', 5, 70, 90], ['off', 5, 71, 90]], True], [148, 70, 0, 71, 0])], [([[['on', 1, 60, 100], ['off', 1, 60, 40]], True], [144, 60, 100, 60, 0]), ([[['on', 16, 60, 100]], False], [159, 60, 100]), ([[['on', 0, 60, 100]], False], None), ([[['on', 17, 60, 100]], False], None), ([[['on', 2, 60, 0]], False], [129, 60, 64]), ([[['on', 2, 60, 0]], True], [145, 60, 0]), ([[['off', 3, 60, 0]], False], [130, 60, 0]), ([[['off', 5, 70, 90], ['off', 5, 71, 90]], True], [148, 70, 0, 71, 0])], [([[['on', 1, 60, 100], ['off', 1, 60, 40]], True], [144, 60, 100, 60, 0]), ([[['on', 2, 60, 0]], False], [129, 60, 64]), ([[['on', 2, 60, 0]], True], [145, 60, 0]), ([[['off', 3, 60, 0]], False], [130, 60, 0]), ([[['on', 1, 60, 100], ['on', 2, 60, 100]], True], [144, 60, 100, 145, 60, 100]), ([[['on', 1, 128, 100]], False], None), ([[['cc', 1, 7, 100]], False], None), ([[['on', 10, 36, 127], ['off', 10, 36, 0], ['on', 10, 38, 127]], True], [153, 36, 127, 36, 0, 38, 127])], [([[['on', 1, 60, 100], ['off', 1, 60, 40]], False], [144, 60, 100, 128, 60, 40]), ([[['on', 1, 60, 100], ['off', 1, 60, 40]], True], [144, 60, 100, 60, 0]), ([[['on', 2, 60, 0]], True], [145, 60, 0]), ([[['on', 1, 128, 100]], False], None), ([[['cc', 1, 7, 100]], False], None), ([[['on', 10, 36, 127], ['off', 10, 36, 0], ['on', 10, 38, 127]], True], [153, 36, 127, 36, 0, 38, 127]), ([[['on', 1, 60, 1]], True], [144, 60, 1]), ([[['off', 5, 70, 90], ['off', 5, 71, 90]], True], [148, 70, 0, 71, 0])], [([[['on', 1, 60, 100], ['off', 1, 60, 40]], False], [144, 60, 100, 128, 60, 40]), ([[['on', 1, 60, 100], ['off', 1, 60, 40]], True], [144, 60, 100, 60, 0]), ([[['on', 1, 60, 100], ['on', 1, 64, 90]], True], [144, 60, 100, 64, 90]), ([[['on', 1, 60, 100], ['on', 1, 64, 90]], False], [144, 60, 100, 144, 64, 90]), ([[['on', 16, 60, 100]], False], [159, 60, 100]), ([[['on', 2, 60, 0]], True], [145, 60, 0]), ([[['on', 10, 36, 127], ['off', 10, 36, 0], ['on', 10, 38, 127]], True], [153, 36, 127, 36, 0, 38, 127]), ([[['off', 5, 70, 90], ['off', 5, 71, 90]], True], [148, 70, 0, 71, 0])]]
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	`[144, 60, 100, 128, 60, 40]`	`[144, 60, 100, 128, 60, 40]`	Passed
oracle 1	`[144, 60, 100, 60, 0]`	`[144, 60, 100, 60, 0]`	Passed
oracle 2	`[144, 60, 100, 64, 90]`	`[144, 60, 100, 64, 90]`	Passed
oracle 3	`[144, 60, 100, 144, 64, 90]`	`[144, 60, 100, 144, 64, 90]`	Passed
oracle 4	`[159, 60, 100]`	`[159, 60, 100]`	Passed
oracle 5	`None`	`None`	Passed
oracle 6	`None`	`None`	Passed
oracle 7	`[148, 70, 0, 71, 0]`	`[148, 70, 0, 71, 0]`	Passed

SHA-256 / f77821a411f7d75b6bafb57d76fbd41e4edc0df6d234c9c78250a03b52106b2e

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 2026-09-29T14:50:06.268202+00:00.

Case digest / a74abedab6879b676ba0c4eecd34f42f7fe94579a1f61ccddd4a33163427c3ed