FA-78584 / Broadcast timecode arithmetic / Member archive

Reverse telecine field attribution: cadence base offset · case 04

With a non-zero phase, fields are attributed as if the cadence started at A.

Member previewVariant 4 · 3 implementations · 9 checks per implementation

Case contract

Fields carry film frames in A2 B3 C2 D3 cadence; film frame 0 has cadence position phase and starts at field 0. Video frame v consists of fields 2v and 2v+1. For order "upper" field 2v is the top field; for "lower" field 2v is the bottom field. Return [film frame in top field, film frame in bottom field, "clean" or "mixed"]; a negative v returns None.

Why this case matters

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

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression: cadence base offset	`[6, 6, "clean"]`	`[8, 8, "clean"]`	Failed

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