ARA Skill

Use this when working on Pulp's optional ARA (Audio Random Access) support or when guiding users who want to build and validate ARA-enabled plugins.

Scope

• Companion APIs: VST3 on macOS + Windows, AU on macOS, CLAP on macOS + Windows
• Primary hosts: Logic (AU), Cubase + Studio One (VST3), Reaper (VST3 or CLAP with ARA extension), Bitwig (CLAP when its ARA extension ships)
• Target ARA version: 2.x (enum value kARAAPIGeneration_2_3_Final = 6)
• Out of scope: ARA 1.x (obsolete), hosting arbitrary ARA plugins (that's a separate host workstream), audio-file chunk authoring tools

Licensing

• ARA SDK is Apache 2.0 — compatible with Pulp's MIT, but we still treat it like AAX / AudioUnitSDK / VST3 SDK: developer-supplied, opt-in, out-of-tree, never committed. tools/deps/audit.py --strict must stay green.
• DEPENDENCIES.md lists ARA SDK under Optional Developer-Supplied Vendor SDKs exactly because of the companion-API carve-out in CLAUDE.md.
• Celemony notes: "Any public release of ARA-enabled software should be based on a tagged public release of the ARA API." Use a tag, not main.

What Users Should Download

The SDK is public on GitHub. Clone with submodules so ARA_API + ARA_Library + ARA_Examples all resolve:

git clone --recurse-submodules --depth 1 \
    https://github.com/Celemony/ARA_SDK.git \
    external/ara-sdk

After cloning, verify:

ls external/ara-sdk/ARA_API/ARAInterface.h     # core C API
ls external/ara-sdk/ARA_Library/PlugIn/ARAPlug.h  # C++11 helpers

Never commit external/ara-sdk/. The external/ prefix keeps it out of cmake --install exports and the repo audit.

Enabling ARA in a Pulp build

Two CMake knobs:

cmake -S . -B build \
    -DPULP_ENABLE_ARA=ON \
    -DPULP_ARA_SDK_DIR=/absolute/path/to/external/ara-sdk

PULP_ENABLE_ARA=ON without PULP_ARA_SDK_DIR fails fast with a clear error. A missing / wrong path fails on ARAInterface.h existence check before any compilation starts.

When enabled, pulp-format is built with PULP_HAS_ARA=1 and the ARA SDK include directory added to its PUBLIC include path. Plugin TUs that want to implement ARA include <ARA_API/ARAInterface.h> directly.

Verifying the integration

Quick smoke:

cmake --build build --target pulp-test-ara
./build/test/pulp-test-ara
# Expect: ara_sdk_compiled_in() → true, ara_sdk_generation() >= 6

A build with PULP_ENABLE_ARA=OFF (the default) must still pass the same tests — ara_sdk_compiled_in() returns false and ara_sdk_generation() returns 0 without failing.

Writing an ARA-aware plugin

1. Override Processor::create_ara_document_controller() to return a concrete AraDocumentController subclass.
2. Use the Pulp-side types from <pulp/format/ara/types.hpp> (AraAudioSource, AraPlaybackRegion, etc.). These are SDK-independent so the plugin TU never pulls the SDK unless it wants to implement a content reader that inspects ARA's C structs directly.
3. Format-adapter companion factories translate between Pulp types and the SDK's C structs.

Using ARA with each adapter

A real ARA::ARAFactory is surfaced out of core/format/src/ara_factory.cpp whenever PULP_HAS_ARA is defined. Hosts reach it via the adapter-specific hook listed below — the integration code is done on the adapter side, so plugin authors only subclass AraDocumentController.

CLAP

Already end-to-end wired: clap_plugin::get_extension(kClapAraFactoryExtension) returns the live factory. Example: core/format/src/clap_adapter.cpp (search for kClapAraFactoryExtension). Validate with ./build/tools/scan-worker/pulp-scan-worker path/to/MyPlug.clap once ARA is initialised.

VST3 (Cubase, Studio One)

The VST3 adapter wires PulpVst3Processor::initialize(FUnknown*) to query IPluginFactory3::setHostContext for the attribute key kVst3AraFactoryContextKey. The plug-in side does nothing beyond subclassing AraDocumentController; the adapter binding is in core/format/src/vst3_adapter.cpp.

AU (Logic Pro)

The AU adapter exposes kAuAraFactoryPropertyKey as the KVO property audioUnitARAFactory on PulpAudioUnit. Logic reads it on scan, caches the factory, and binds a document controller per loaded plug-in instance.

Verifying live (not a stub)

# Build with the SDK on:
cmake -S . -B build -DPULP_ENABLE_ARA=ON -DPULP_ARA_SDK_DIR=$PWD/external/ara-sdk
cmake --build build --target pulp-test-ara

# Run the live-factory tests (guarded on PULP_HAS_ARA):
./build/test/pulp-test-ara '[factory]'

The ABI-conformance test asserts that the factory's highestSupportedApiGeneration is kARAAPIGeneration_2_3_Final, that createDocumentControllerWithDocument returns a non-null ARADocumentControllerInstance, and that getFactory() round-trips back to the same factory pointer.

Known gotchas

• All time fields are seconds (double), not samples. Pulp's AraPlaybackRegion matches ARAPlaybackRegionProperties; adapters convert to samples only at explicit sample-domain APIs.
• Threading contract: ARA's render thread, document-editing thread, and main thread map to Pulp's audio / UI / main threads. Do not block across them; consult docs/reference/host-thread-rules.md.
• Host quirks are real. Logic's ARA integration differs from Cubase's. Budget time for host-specific workarounds.
• host_supports_ara() currently returns false even with the SDK compiled in until the format-adapter companion factories are wired.
• Factory is valid but controller interface is stubs. When PULP_HAS_ARA is on, ara_companion_factory_for() returns a real ARA::ARAFactory. Its createDocumentControllerWithDocument returns a valid ARADocumentControllerInstance, but every call on the controller interface is a no-op until plug-ins override them. Hosts see a working factory; they just cannot edit audio yet.

Planning & issue tracking

• Spec: planning/production-readiness/06-ara.md
• Status: planning/production-readiness/STATUS.md (ARA / workstream 06 section)
• Tracking: #219

Skill maintenance

Path map: tools/scripts/skill_path_map.json. Add entries for core/format/src/ara*, core/format/include/pulp/format/ara*, external/ara-sdk (so non-committed work still triggers skill sync checks on related source changes).