FA-81809 / MIDI event timing / Member archive

MIDI Time Code quarter-frame assembly: rate bits leak into the hour · case 04

At 25 fps the rate-code bits are folded into the hours field, so 01:02:03 decodes with hour 9 after wrapping.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

Input the data bytes of received quarter-frame messages. The last eight must carry piece numbers 0..7 (high nibble) in order; low nibbles give frames (pieces 0,1 as low/high nibble), seconds (2,3), minutes (4,5) and hours (6 low nibble, piece 7 bit 0 as hours bit 4); piece 7 bits 1-2 give the rate code (0: 24, 1: 25, 2: 30 drop, 3: 30 fps). The reported time is the decoded time plus 2 frames, carried into seconds, minutes and hours (mod 24). Return [h, m, s, f, rate_code] or None.

Why this case matters

MIDI sequencers, file readers and synth drivers depend on exact event ordering and tick/time arithmetic.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
oracle 0	`[9, 30, 15, 12, 2]`	`[17, 30, 15, 12, 2]`	Failed

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