Plugin Hosting

Host VST3 and CLAP plugins, in sandboxed child processes so a crashing plugin never kills the show.

✅ Shipped · v0.5.0 · sandboxing v0.7.0

What it does

Stardust hosts third-party audio plugins to provide the actual sounds. You drag a plugin (e.g. Spitfire BBC SO Discover, Surge XT, MuseSounds Strings) into a Patch’s VST chain, configure its parameters, and the plugin processes incoming MIDI into output audio. Multiple plugins per Patch are supported — for layered sounds, splits, or effects chains.

Supported formats

Format	Status	Notes
VST3	MVP (v0.2)	The industry standard. Spitfire, MuseSounds, Surge XT, Vital, Dexed, all commercial libraries.
CLAP	v0.3	Open-source modern format. Smaller ecosystem (mostly synths/effects), but high quality.
AU	v2.0+	macOS-only Apple format. Some users prefer it for AU-specific plugins.
VST2	Never	Deprecated by Steinberg. We won’t ship VST2 support.

Plugin sandboxing

The single biggest reliability decision in Stardust: every plugin runs in its own child process.

If a plugin segfaults — and they do, especially older third-party C++ code:

The audio engine catches the disconnect on the next audio callback
Sends all-notes-off to all channels
Either restarts the plugin or falls back to silence + sustain-off
UI notification toast: “Spitfire BBC SO crashed — restarted”
If a plugin crashes twice, it’s quarantined for the rest of the session

Most existing live hosts run plugins in-process for performance reasons, which means a single plugin crash takes the host down with it. Stardust accepts the ~1 ms IPC overhead to keep that from happening. See Comparison for how this compares across hosts, and Plugin Sandboxing for IPC and process-model details.

Latency cost of sandboxing

Plugin process IPC adds ~1 ms of latency via shared-memory ring buffers. Worth every microsecond — the reliability gain is enormous.

See Latency Budget.

Plugin parameter handling

Once a plugin is loaded:

Every parameter is exposed in the Patch editor
Parameters can be mapped to MIDI controls via MIDI Learn
Plugin state (current parameter values) is saved per-Patch
Multiple instances of the same plugin can be loaded in different Patches with different state
Plugin GUI displays in the patch editor’s bottom GUI dock by default (tab strip per loaded plugin in the active patch); pop-out button moves it to a floating window per the user’s per-plugin preference. Per-plugin placement persists across patch reloads. See locked decisions.

Plugin discovery

Auto-scan on first run (with progress UI)
Default scan folders:
- macOS: ~/Library/Audio/Plug-Ins/VST3, /Library/Audio/Plug-Ins/VST3
- Windows: C:\Program Files\Common Files\VST3
Custom folders configurable in Settings → Plugins
CLAP folders similarly default + customizable (v0.3)
Plugin metadata cached for fast re-scan
Quarantined plugins surfaced with manual re-enable

See Audio I/O for related setup.

VST3 implementation strategy

v0.2 uses a small C++ shim around the Steinberg VST3 SDK, called from Rust via FFI. The shim is ~1-2k LOC of C++ following Steinberg’s sample host code.

We chose this over:

vst3-sys (pure Rust): Too immature, lags SDK updates, smaller community
JUCE plugin host: Heavy dependency, GPL-incompatible without commercial license
Native Rust SDK from scratch: 3-6 months of dedicated expert work

The C++ shim is hidden behind a clean Rust API in Overture. If a pure Rust alternative emerges, we can swap internals without breaking the public API.

See VST3 Shim decision.

CLAP implementation (v0.3)

CLAP support uses clack, the leading Rust CLAP host. Adds ~1 week of work; gives users access to Surge XT, Vital, u-he plugins in CLAP mode, and the growing CLAP ecosystem.

See CLAP decision.

Test plugins for development

Free VST3 plugins for validating different behaviors:

Plugin	Why we test with it
Surge XT	Open-source, hugely capable, CLAP version available
Spitfire BBC SO Discover	RAM-heavy sample library
Spitfire LABS	Variety of free instruments
MuseSounds	Orchestral, CPU-heavy on streaming
Vital (free)	Modern wavetable synth, modulation-heavy
Dexed	Small footprint, lots of params (DX7 emulator)
Sforzando	SFZ player — for community-shared samples
Helm	Open-source subtractive synth
Valhalla Supermassive	Effect plugin in chain

This stack validates VST3 hosting under all production conditions.

Phase-by-phase status

Phase	What’s available
v0.2	VST3, in-process, single plugin per chain, basic UI
v0.3	VST3 + CLAP, sandboxed, multi-plugin chains, crash recovery
v0.4	Full UI integration with chains, mappings, transitions
v0.5	Built-in effects rack (EQ, reverb, comp) alongside plugins
v2.0+	AU on macOS