effectcraft/crates/aep/README.md

# effectcraft-aep

After Effects projects (`.aep`, `.aepx`) in one crate, the way `effectcraft-lottie` handles Lottie:

- `container`: reads and writes the container as a lossless chunk tree, with a typed, read-only
  view (below; its API is re-exported at the crate root);
- `import`: maps the typed view into an EffectCraft project and reports everything it does not
  import ([`docs/aep-import.md`](../../docs/aep-import.md));
- `export`: writes an EffectCraft project as an `.aep` with every chunk built in code, and reports everything it does not export
  ([`docs/aep-export.md`](../../docs/aep-export.md)).

No file access: callers pass bytes, so the crate builds for wasm32.

## Container

An `.aep` is a `RIFX` container (big-endian RIFF) with form type `Egg!`: chunks of a 4-byte id, a
big-endian `u32` size and a body padded to an even length; `LIST` chunks start with a 4-byte list
type followed by chunks. `parse` builds the tree, `write` serialises it, and for every input that
parses, `write(parse(x)) == x` byte for byte (container and chunk sizes are recomputed from the
tree; pad bytes, odd bodies and the bytes after the container, an XMP packet, are kept).

The XML form of a project (`.aepx`) is read into the same tree by `read_aepx` (a small bounded
XML tokenizer, no dependency); `parse_any` picks the reader by content, so the typed view and the
importer take either form. The mapping is in `docs/aep-format.md`, section 1.

Bodies that look like lists but are not chunk sequences (for example `LIST btdk`, raw text) stay
opaque rather than failing the parse. Input is untrusted: sizes are checked against the remaining
input, nesting and chunk count are bounded (`Limits`), nothing is allocated from a declared size,
and truncated or damaged files return `Err` (or, inside the container, an opaque body).

The container layer decodes no chunk body. On top of it, a typed view (`Project`, `Item`, `Comp`, `Layer`,
`Property`, ...) reads the fields whose layout was verified against the values the test files were made
with: layer and composition headers (switches, exact times and time stretch, size, frame rate, work area, shutter phase, display start, renderer),
static transform values in After Effects' units with the "absent = default" rule, keyframe records
(interpolation sides, ease per component, plain and spatial templates), Time Remapping, expressions with their enable switch, effect
instances and parameter values, masks and bezier paths with tangents, shape layer groups, text documents
(paragraph and style runs, box, justification, tracking, faux styles, caps, leading), markers with
duration, strings and cue data, cameras and lights with their options, footage (stills, audio, image
sequences), solids and precomp links. Every accessor returns `Option`/an empty list on damaged data and never
panics. Which fields are verified, which are not decoded, and how it was found is in
[`docs/aep-format.md`](../../docs/aep-format.md).

## Specifications

Public specifications used for parts the format embeds:

- ICC.1:2010: the profile description of a working-space profile (a v2 `desc` or a v4 `mluc`
  tag), from which the working space's name is read (`container/settings.rs`).
- RFC 4648 (base64): the profile data in the project's colour settings JSON (read, and written
  by the exporter).
- The exporter's own colour profiles (`export/icc.rs`): ICC.1:2010 version 4.3 display profiles
  with ITU-R BT.709 primaries, D65 white, a D50 PCS and a Bradford adaptation, the IEC 61966-2-1
  sRGB curve or a 2.4 power curve; the profile ID is the MD5 of RFC 1321.

## Clean room

Everything here comes from our own observations: project files that we generated ourselves with
After Effects, one change per file, compared byte by byte. No source code or format
documentation of another `.aep` reader or writer was used, and no Adobe asset is used. The test fixtures are such generated files
(own test data): a few combined projects, one composition per case (`tests/fixtures/CASES.md`;
the generator is in `tests/fixtures/tools/`). They are not in this repository but in
[storytold/effectcraft-corpus](https://github.com/storytold/effectcraft-corpus), with their
attribution, the generation notes and the inspection of their embedded content.
`cargo xtask aep-corpus` fetches them at the commit pinned in `tests/fixtures/corpus.lock`, checks
every file against the SHA-256 listed there and only then installs them in `corpus/aep` (ignored by
git). The tests read them from the folder named by the `EFFECTCRAFT_AEP_FIXTURES` environment
variable (opt-in; set `EFFECTCRAFT_AEP_FIXTURES_REQUIRED=1` too, so that a missing project fails). The
tests reach them only through `tests/it/common/mod.rs`, which hands a test its case as a project
of its own cut from the combined file; a test whose fixture is missing (or with the variable not
set) prints `SKIPPED: fixture <name> missing` and passes.

`tests/fixtures/synthetic.aep` (115 KB) is the one project in the repository: made in After Effects 2026
with the working space set to None (one composition, an image sequence of three 8x8 PNGs, a
solid, a folder, a Levels and a Glow effect with expressions). Every After Effects project embeds
the working space's ICC profile (HP sRGB IEC61966-2.1 for the default) in a JSON settings chunk;
the one `Utf8` chunk of this file that held a profile was replaced by `{}`, and nothing else was
changed. The tests in `tests/it/import/synthetic.rs` damage copies of it and need no other file.

## Tools

- `tests/fixtures/tools/`: the generator of the test projects (regenerates the corpus with After
  Effects; its README says how).
- `examples/aepdump.rs`: prints the chunk tree of a file (ids, sizes, short data, match names):
  `cargo run -p effectcraft-aep --example aepdump -- file.aep`.
- `examples/stubicc.rs`: replaces every embedded ICC profile of a saved project by a stub that keeps
  only the profile's description: the JSON `colorProfileData` of the working space (any white space
  around the colon, `\/` escapes, quotes as `&quot;`) in an `.aep` chunk or the `.aepx` text, and a raw
  profile of an imported image (an `.aep` chunk, or the `bdata` hex of an `.aepx`):
  `cargo run -p effectcraft-aep --example stubicc -- in.aep out.aep`. A profile it cannot replace
  stops it before anything is written. The importer reads the working space's name from the
  description only, so the project imports the same; no vendor colour data stays in the test
  project. Check the result independently, not by the tool's count (the corpus repository has
  `tools/aep/inspect-embedded.py`, which scans the raw bytes, base64 and hex).