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Stardust

AU Hosting

Native Audio Unit (AU) plugin support on macOS. The Apple-format equivalent of VST3.

💭 v1.x or v2.0+

What it does

Hosts Audio Unit plugins on macOS — the native Apple plugin format used in Logic, GarageBand, MainStage. Stardust treats AU plugins identically to VST3: load into a Patch’s chain, route MIDI in, get audio out, parameter mapping, MIDI Learn, all the same.

Why v2.0+

Two reasons we defer AU:

  1. VST3 is the universal format. Almost every commercial plugin ships VST3, including most that also ship AU. So VST3 covers the use cases first.
  2. AU hosting requires native Objective-C++ bridging. No good Rust SDK exists; we’d write a small Obj-C++ module bridged to Rust. Similar effort to the VST3 shim.

So we ship 1.0 with VST3 + CLAP (cross-platform), and add AU as a macOS-only v2.0+ enhancement.

Implementation strategy

Similar to VST3:

  1. Write a small Obj-C++ module that wraps Apple’s AU host APIs (AudioToolbox, AudioUnit)
  2. Expose a clean C ABI for Rust to call
  3. Use the same plugin orchestration in Overture as for VST3 (sandboxing, parameter mapping, voice tracking)
  4. UI integration identical — users don’t see the difference between AU and VST3 plugins

What plugins benefit

Mostly:

  • Apple’s own plugins — Alchemy, Sculpture, ES2, Retro Synth (Logic-bundled, AU-only)
  • A few macOS-only third-party plugins that didn’t ship VST3
  • Some legacy plugins that have AU versions but discontinued VST3

For most users, VST3 covers what they need. AU is the “completeness” feature.

Windows users not affected

AU is macOS-only by Apple definition. Windows users use VST3 + CLAP. This is one of the rare areas where macOS users get a feature Windows users don’t — but Apple-only formats are inherently platform-specific.