Map Logic ProjectData chunk payloads (starts with AuRg or Trak)

[sepehrsadri]

The Logic ProjectData container is decoded — 24-byte header, magic 23 47 C0 AB, little-endian FourCC records — and we can enumerate 22 chunk tags across 2,069 records. The payloads are not decoded.

That gap is the difference between "3 regions were added" and "the region 'Deep Down Shaker.1' moved from bar 12 to bar 16".

What is already known (see docs/FORMATS.md)

Tag	Meaning	Observed across saves
AuFl	audio files	35 → 37 (matches MetaData.plist exactly)
AuCU	plugins	70 → 76 → 265
AuRg	regions	79 → 90 → 96
Trak	tracks	248 → 256 → 260
MSeq/EvSq	sequences	147 → 155 → 159

Region names are already readable directly from AuRg payloads.

The task

Pick one tag and map its payload structure: field offsets, types, and meaning. AuRg (regions) or Trak (tracks) are the highest value. Document findings in docs/FORMATS.md and, ideally, add a parser to experiments/.

Method that worked for the container

Diff the same record across sequential saves in Alternatives/000/Project File Backups/00..08 where you know what the user changed, and correlate with MetaData.plist.

Bonus: this also covers GarageBand. It uses the same container (23 47 C0 AB, gnoS), differing only in a version word — so one parser serves both.

⚠️ Work only on copies. Never modify a real project.