FA-81404 / MIDI event timing / Member archive

Standard MIDI File header chunk reader: zero ticks per quarter accepted · case 04

A header with division 0 is returned as ppq 0, which later divides by zero in timing code.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

Input the bytes of a header chunk: "MThd", a 32-bit big-endian length (>= 6; extra bytes ignored but must be present), 16-bit format (0, 1, 2), 16-bit track count (nonzero; exactly 1 for format 0) and 16-bit division. If bit 15 of division is set, the high byte is a negative two's-complement frame rate (24, 25, 29, 30) and the low byte ticks per frame; otherwise division is ticks per quarter note (nonzero). Return a dict 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 5	`{"format": 1, "ppq": 0, "tracks": 2}`	`null`	Failed

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