VST3: adopt a permissively-licensed binding now that the SDK is MIT (tracking)

[lvpsxakatiempo]

Summary

Now that Steinberg relicensed the VST3 SDK to MIT (VST 3.8, Oct 2025), nih-plug's VST3 export is the last thing forcing GPLv3 on otherwise-permissive plugins. This is a tracking issue for migrating the VST3 wrapper from the GPLv3-only vst3-sys to a permissively-licensed binding, so closed-source VST3 plugins become possible.

(Consolidating the licensing angle from #135 — which is framed around DPF's Travesty — and noting #236 below. Happy to close as a dup if you'd rather keep everything in #135.)

The blocker today

• The vst3 feature pulls robbert-vdh/vst3-sys (fix/drop-box-from-raw), which is GPLv3-only.
• src/wrapper/vst3/ (~4k LOC, ~110 references to vst3_sys) is written directly against that crate's COM API, so the GPLv3 propagates to any VST3 build.
• A CLAP build is fine (clap-sys is MIT/Apache) — only VST3 is affected.

What changed / what's available now

1. SDK is MIT (Oct 2025): the original reason vst3-sys was GPLv3 (it derived from a GPL/proprietary SDK) no longer applies. The long "is the VST3 interface copyrightable" debate in Couldn't the vst3 export be replaced by DPF's Travesty custom vst3 implementation? #135 is largely moot — the headers are MIT now.
2. Permissive, generated bindings already exist and are maintained: coupler-rs/vst3-rs and micahrj/vst3-sys, both MIT OR Apache-2.0, regenerated from the headers. The RustAudio/vst3-sys maintainer now recommends them himself.
3. Move to non-forked vst3-sys crate #236 ("move to non-forked vst3-sys") does not fix licensing — upstream RustAudio/vst3-sys is also GPLv3-only. The relicensing path through that crate looks unlikely (see VST3 com interface issue / fix #58), so the durable fix is the generated bindings.

Proposed scope

• Decide the target binding (coupler-rs/vst3-rs looks like the strongest candidate; it's by the same author as clap-sys).
• Port src/wrapper/vst3/* from the vst3-sys COM API to the chosen crate.
• Verify host compatibility (FL Studio, Cubase, Reaper, Bitwig, Ableton) and that the persisted VST3_CLASS_ID is unaffected (so existing saved sessions keep loading).
• Flip the crate's license note for VST3 builds accordingly.

Offer to help

I maintain a commercial multi-format sampler on nih-plug (CLAP shipping; VST3 blocked only by this). I'm happy to help with the port and to test a migration against a large real-world surface — SFZ / SF2 / DLS / EXS24 / Akai / DecentSampler / etc., 64-voice polyphony, multi-output, automation, persisted state. Just let me know if a migration is something you'd accept and I'll start on a branch.

Thanks for nih-plug — it's a genuinely great framework, and this is the one thing keeping commercial VST3 plugins off it.

[d4kine]

I'd totally appreciate this, there's no reason to be still GPL when Steinberg made it MIT :)

[JuxGD]

NIH-plug isn't being actively maintained currently, there's an actively maintained fork (that's linked in the readme btw :p) at https://codeberg.org/RustAudio/nice-plug