[alehel]

Part 6 of 10 of #395, split in the order FredApps recommended there. Each PR in the stack targets main and builds on the one before it, so until the PRs below it merge, GitHub also shows their commits. This PR's own change is the last commit: 80e604c.

What the series is for

SoundCraft, FilmCraft and EffectCraft each wrote their own audio encoders and decoders, and several overlap: three WAV/AIFF writers, two FLAC encoders, and FilmCraft's AAC and MP1/MP2 decoders next to symphonia's. The series moves them into craft-libs so each format has one implementation that every app uses. Where two implementations overlapped, both were measured against ffmpeg and the reference tools and the stronger one was kept; #395 has the comparison.

When all ten parts have merged:

• craft-media holds the containers (MP4/MOV, Matroska/WebM, Ogg), bit I/O, and the types every codec crate needs to take a track from a demuxer: CodecId, CodecParams, Container, ByteSource.
• craft-audio holds the audio codecs and WAV/AIFF file I/O, each format behind its own feature, so an app compiles only what it uses. symphonia stays as a fallback for formats with no native decoder yet (MP3, FLAC decoding, ALAC, Vorbis, CAF, ADPCM, A-law/µ-law) until those are written.
• A video crate can later sit beside craft-audio on craft-media, reusing the demuxers, CodecParams and the testkit. The two codec crates never depend on each other, so audio-only apps such as SoundCraft never compile video code.

%%{init: {"flowchart": {"htmlLabels": false}}}%%
graph TD
    SC["SoundCraft"] --> A
    FC["Film-/EffectCraft"] --> A
    FC -.-> V
    A["craft-audio<br/>audio codecs, file I/O"] --> M
    V["craft-video<br/>video codecs (later)"] -.-> M
    M["craft-media<br/>containers, bit I/O, shared types"]
    classDef later stroke-dasharray: 5 5
    class V later

Loading

Dashed: the planned video crate.

No app changes in the series. Each app keeps its own codec code until it switches to craft-audio in its own follow-up. #395 has the full design, the comparison of overlapping implementations and the migration notes for apps.

The ten parts

#	PR	Merged
1	#439 craft-media: shared codec identifiers, one ByteSource, the testkit	✅
2	#440 craft-media: Ogg demuxer	✅
3	#441 craft-audio: core types, WAV/AIFF read and write, peaks, symphonia
4	#442 craft-audio: FLAC encoder
5	#443 craft-audio: AAC decoder
6	#444 craft-audio: AAC encoder ← this PR
7	#445 craft-audio: Opus decoder
8	#446 craft-audio: Opus encoder
9	#447 craft-audio: AC-3 and E-AC-3 decoder
10	#448 craft-audio: MP1/MP2 decoder

All ten together are #395's final tree on current main, plus one change from the review: actions/checkout is pinned to a commit SHA in audio.yml. Each PR builds, passes clippy for every feature set and passes its tests on its own.

What this adds

FilmCraft's AAC-LC encoder behind aac-encode, which encode now includes. It has a psychoacoustic model, window switching, M/S, TNS, a bit reservoir, CBR and VBR, 1–8 channels and optional ADTS framing.

• rayon encodes channels in parallel.
• aac::aac_order maps WAV order to the encoder's input order.
• Settings the encoder cannot use are aac::Error::InvalidSettings, which converts to AudioError::Encode.
• The tests that need AAC written by our own encoder come with it: the encoder oracle and robustness tests, packet concealment, and TrackDecoder on ADTS without extradata.

Known issue in the ported code

From CodeRabbit on #395, ported unchanged from FilmCraft: the encoder accepts a NaN VBR quality. It will get its own issue and fix.

Testing

Run locally on this branch, as audio.yml runs them:

• cargo fmt --check
• clippy with -D warnings for each feature in the workflow's loop on its own, and for all features
• rustdoc with -D warnings (all features, decode-native, lossless-encode)
• WASM cargo check (all features, lossless-encode)
• the workflow's subset test runs
• cargo test -p craft-audio --all-features with CRAFT_MEDIA_REQUIRE_ORACLES=1 and ffmpeg 9.0.2

Not run locally: the MSRV job (1.95).

🤖 Generated with Claude Code

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