FA-78386 / Broadcast timecode arithmetic / Open access

Frame count to timecode label with frame pairs: pair index · case 01

Frame-pair fields restart halfway through each second.

Verified by executionVariant 1 · 9 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The pair index wraps modulo half the rate instead of halving the frame.

THE FAILURE

The pair index wraps modulo half the rate instead of halving the frame.

Unsuccessful approach: Rounding up the pair index groups frames into the wrong pairs.

Case contract

Convert a frame count (any integer, wrapped modulo 24 hours) to HH:MM:SS:FF. For fps above 30 the frame field counts frame pairs (frame//2) and the last separator is "." for the second frame of a pair and ":" otherwise.

Why this case matters

Timecode arithmetic errors misplace edits, commercial breaks and captions against the broadcast clock.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(frames, fps):
    day=24*3600*fps
    frames%=day
    fr=frames%fps
    s=frames//fps
    hh,mm,ss=s//3600,s//60%60,s%60
    if fps>30:
        return '%02d:%02d:%02d%s%02d'%(hh,mm,ss,'.' if fr%2 else ':',fr%(fps//2))
    return '%02d:%02d:%02d:%02d'%(hh,mm,ss,fr)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression: pair index', [3, 50], '00:00:00.01'), ('regression variant: pair index', [4147205, 48], '00:00:00.02'), ('partial repair probe: pair index', [216007, 60], '01:00:00.03'), ('partial repair variant: pair index', [-1, 50], '23:59:59.24'), ('boundary control', [0, 25], '00:00:00:00'), ('boundary control', [30, 30], '00:00:01:00'), ('normal control', [-1, 25], '23:59:59:24'), ('normal control', [1803, 30], '00:01:00:03'), ('normal control', [8166989, 30], '03:37:12:29')], [('regression: pair index', [2, 50], '00:00:00:01'), ('regression variant: pair index', [-5184003, 60], '23:59:59.28'), ('partial repair probe: pair index', [8640011, 50], '00:00:00.05'), ('partial repair variant: pair index', [49, 50], '00:00:00.24'), ('boundary control', [-1, 25], '23:59:59:24'), ('boundary control', [0, 25], '00:00:00:00'), ('normal control', [5184000, 60], '00:00:00:00'), ('normal control', [-4622105, 30], '05:12:09:25'), ('normal control', [2, 30], '00:00:00:02')], [('regression: pair index', [216007, 60], '01:00:00.03'), ('regression variant: pair index', [1, 48], '00:00:00.00'), ('partial repair probe: pair index', [3745221, 48], '21:40:25.10'), ('partial repair variant: pair index', [-4147203, 48], '23:59:59.22'), ('boundary control', [2160000, 25], '00:00:00:00'), ('boundary control', [-1, 25], '23:59:59:24'), ('normal control', [2592005, 30], '00:00:00:05'), ('normal control', [2592000, 30], '00:00:00:00'), ('normal control', [1, 25], '00:00:00:01')], [('regression: pair index', [8640011, 50], '00:00:00.05'), ('regression variant: pair index', [2, 48], '00:00:00:01'), ('partial repair probe: pair index', [4147205, 48], '00:00:00.02'), ('partial repair variant: pair index', [180007, 50], '01:00:00.03'), ('boundary control', [30, 30], '00:00:01:00'), ('boundary control', [2160000, 25], '00:00:00:00'), ('normal control', [48, 48], '00:00:01:00'), ('normal control', [2591999, 30], '23:59:59:29'), ('normal control', [2073605, 24], '00:00:00:05')], [('regression: pair index', [3745221, 48], '21:40:25.10'), ('regression variant: pair index', [-4147203, 48], '23:59:59.22'), ('partial repair probe: pair index', [4319999, 50], '23:59:59.24'), ('partial repair variant: pair index', [4320005, 50], '00:00:00.02'), ('boundary control', [0, 25], '00:00:00:00'), ('boundary control', [30, 30], '00:00:01:00'), ('normal control', [0, 48], '00:00:00:00'), ('normal control', [29, 30], '00:00:00:29'), ('normal control', [2, 25], '00:00:00:02')]]
for label, args, expected in fixtures[N-1]:
    check(label, 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
regression: pair index	`00:00:00.03`	`00:00:00.01`	Failed
regression variant: pair index	`00:00:00.05`	`00:00:00.02`	Failed
partial repair probe: pair index	`01:00:00.07`	`01:00:00.03`	Failed
partial repair variant: pair index	`23:59:59.24`	`23:59:59.24`	Passed
boundary control	`00:00:00:00`	`00:00:00:00`	Passed
boundary control	`00:00:01:00`	`00:00:01:00`	Passed
normal control	`23:59:59:24`	`23:59:59:24`	Passed
normal control	`00:01:00:03`	`00:01:00:03`	Passed
normal control	`03:37:12:29`	`03:37:12:29`	Passed

SHA-256 / aa9e78120c16f2f0a59bc563641293b6474b3a3d6d600284a878a4aca1ebe22b

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(frames, fps):
    day=24*3600*fps
    frames%=day
    fr=frames%fps
    s=frames//fps
    hh,mm,ss=s//3600,s//60%60,s%60
    if fps>30:
        return '%02d:%02d:%02d%s%02d'%(hh,mm,ss,'.' if fr%2 else ':',(fr+1)//2)
    return '%02d:%02d:%02d:%02d'%(hh,mm,ss,fr)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression: pair index', [3, 50], '00:00:00.01'), ('regression variant: pair index', [4147205, 48], '00:00:00.02'), ('partial repair probe: pair index', [216007, 60], '01:00:00.03'), ('partial repair variant: pair index', [-1, 50], '23:59:59.24'), ('boundary control', [0, 25], '00:00:00:00'), ('boundary control', [30, 30], '00:00:01:00'), ('normal control', [-1, 25], '23:59:59:24'), ('normal control', [1803, 30], '00:01:00:03'), ('normal control', [8166989, 30], '03:37:12:29')], [('regression: pair index', [2, 50], '00:00:00:01'), ('regression variant: pair index', [-5184003, 60], '23:59:59.28'), ('partial repair probe: pair index', [8640011, 50], '00:00:00.05'), ('partial repair variant: pair index', [49, 50], '00:00:00.24'), ('boundary control', [-1, 25], '23:59:59:24'), ('boundary control', [0, 25], '00:00:00:00'), ('normal control', [5184000, 60], '00:00:00:00'), ('normal control', [-4622105, 30], '05:12:09:25'), ('normal control', [2, 30], '00:00:00:02')], [('regression: pair index', [216007, 60], '01:00:00.03'), ('regression variant: pair index', [1, 48], '00:00:00.00'), ('partial repair probe: pair index', [3745221, 48], '21:40:25.10'), ('partial repair variant: pair index', [-4147203, 48], '23:59:59.22'), ('boundary control', [2160000, 25], '00:00:00:00'), ('boundary control', [-1, 25], '23:59:59:24'), ('normal control', [2592005, 30], '00:00:00:05'), ('normal control', [2592000, 30], '00:00:00:00'), ('normal control', [1, 25], '00:00:00:01')], [('regression: pair index', [8640011, 50], '00:00:00.05'), ('regression variant: pair index', [2, 48], '00:00:00:01'), ('partial repair probe: pair index', [4147205, 48], '00:00:00.02'), ('partial repair variant: pair index', [180007, 50], '01:00:00.03'), ('boundary control', [30, 30], '00:00:01:00'), ('boundary control', [2160000, 25], '00:00:00:00'), ('normal control', [48, 48], '00:00:01:00'), ('normal control', [2591999, 30], '23:59:59:29'), ('normal control', [2073605, 24], '00:00:00:05')], [('regression: pair index', [3745221, 48], '21:40:25.10'), ('regression variant: pair index', [-4147203, 48], '23:59:59.22'), ('partial repair probe: pair index', [4319999, 50], '23:59:59.24'), ('partial repair variant: pair index', [4320005, 50], '00:00:00.02'), ('boundary control', [0, 25], '00:00:00:00'), ('boundary control', [30, 30], '00:00:01:00'), ('normal control', [0, 48], '00:00:00:00'), ('normal control', [29, 30], '00:00:00:29'), ('normal control', [2, 25], '00:00:00:02')]]
for label, args, expected in fixtures[N-1]:
    check(label, 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
regression: pair index	`00:00:00.02`	`00:00:00.01`	Failed
regression variant: pair index	`00:00:00.03`	`00:00:00.02`	Failed
partial repair probe: pair index	`01:00:00.04`	`01:00:00.03`	Failed
partial repair variant: pair index	`23:59:59.25`	`23:59:59.24`	Failed
boundary control	`00:00:00:00`	`00:00:00:00`	Passed
boundary control	`00:00:01:00`	`00:00:01:00`	Passed
normal control	`23:59:59:24`	`23:59:59:24`	Passed
normal control	`00:01:00:03`	`00:01:00:03`	Passed
normal control	`03:37:12:29`	`03:37:12:29`	Passed

SHA-256 / 6e0296b77f07de5ba939619e2efb8b5fd110297999412d4728f64ef7a4dc3d60

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 9 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

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Verification & scope

A deterministic bounded teaching model with a stipulated toy contract; it does not claim conformance to SMPTE or any broadcast standard. 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 2026-09-29T14:49:34.690763+00:00.

Case digest / 3283c6052d5b9e0cf617f02ba679b9c233e79ce7b20a9826fa83770a2100c6bc