FA-81407 / MIDI event timing / Member archive

Track event parser with running status: one-byte messages recognised only on channel 1 · case 02

A program change on channel 2 (C1) swallows the next delta byte as a second data byte and desynchronises the track.

Member previewVariant 2 · 3 implementations · 8 checks per implementation

Case contract

Input the bytes of a track body: each event is a variable-length delta then either a meta event (FF type len data...), a status byte (bit 7 set) with its data bytes, or data bytes reusing the previous channel status (running status). Program change (Cx) and channel pressure (Dx) take one data byte, other channel messages two. Meta events cancel running status. Return [absolute tick, status, data...] for channel events and [tick, "meta", type] for meta events, or None on truncation or data without a running status.

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 6	`null`	`[[0, 193, 5], [0, 193, 6]]`	Failed

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