Timecode Math Calculator

Inspectable records

Ledger state

The current ledger marks this instrument verified clean within the source-bound verification corpus.

Area

Audio, Music, Photography & Color

Tranche

tranche-4

Evidence ID

t4-274

Ledger rows

1

No ledger note is attached.

Review findings

NEEDS_REVIEW because the exact drop-frame correction algorithm and the frame-rate-conversion policy are ambiguous. The vectors assume SMPTE-style 29.97 DF and 59.94 DF, absolute frame-index arithmetic, elapsed-time-preserving conversion, and exact target-frame results.

Formula and scope findings

• The stated formula is correct for non-drop-frame timecodes when fps is an integer nominal frame rate and ff is a frame number in the range 0 through fps-1.
• The formula is incomplete for 29.97 and 59.94 drop-frame timecode. It must use nominal rates of 30 and 60 respectively, with 2 dropped frame numbers per non-tenth minute at 29.97 DF and 4 dropped frame numbers per non-tenth minute at 59.94 DF.
• The drop-frame correction algorithm is not specified, including the exact valid-rate mapping, dropped-frame count, minute-boundary exceptions, and conversion between absolute frame numbers and displayed timecode.
• Frame-rate conversion is underspecified: the spec does not state whether conversion preserves elapsed time, absolute frame count, or display labels, nor how fractional-frame results are rounded.
• The spec does not define behavior for subtraction producing negative results, timecode rollover, or whether results may exceed 24 hours.

Unit assumptions

• fps means frames per second; 29.97 and 59.94 are treated as exact nominal labels for display but as 30000/1001 and 60000/1001 for elapsed-time calculations.
• Non-drop-frame calculations use an integer nominal frame rate, such as 24 or 30.
• 29.97 DF uses a 30-frame nominal rate and drops frame numbers ;00 and ;01 at the start of every minute except each tenth minute.
• 59.94 DF uses a 60-frame nominal rate and drops frame numbers ;00 through ;03 at the start of every minute except each tenth minute.
• The test-vector frame totals for drop-frame cases are absolute nominal frame indices after applying the SMPTE drop-frame correction.
• Frame-rate conversion in the third vector preserves elapsed time exactly and uses a target frame rate of 30 fps.

Boundary hardening

BREAK_CLAIMED · SELF_FLAGGED

The 29.97 DF domain contains skipped frame labels that must be rejected, and subtraction can produce a negative result whose display convention is unspecified. A calculator that blindly applies arithmetic or silently wraps negatives can return a misleading result.

Errata and corrections

No applied erratum is attached to this unique-name record.

Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

{
  "inputs": {
    "timecode_a": "01:02:03:12",
    "timecode_b": "00:00:10:12",
    "operation": "add",
    "frame_rate": 24,
    "mode": "non-drop-frame"
  },
  "expected_outputs": {
    "resulting_timecode": "01:02:14:00",
    "total_frames": 89616
  },
  "working": "At 24 fps: A = 1*3600*24 + 2*60*24 + 3*24 + 12 = 86400 + 2880 + 72 + 12 = 89364 frames. B = 0*86400 + 0*1440 + 10*24 + 12 = 252 frames. Sum = 89364 + 252 = 89616 frames. Convert back: 89616 - 86400 = 3216; 3216 - 2*1440 = 336; 336 - 14*24 = 0. Result = 01:02:14:00."
}

Related workflows

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json · VERIFIED_CLEAN
• evidence-tranche4/tranche4-results.json
• BOUNDARY_HAZARD_CATALOG.json