MPVST

Programmable VST3 instruments and audio effects backed by dedicated MicroPython engine processes. One bundle ships a whole library: every audioinstruments module and every audioeffects class appears in the DAW's browser under its own name and category - TR-808 under Instrument|Drum, Tape Delay under Fx|Delay - alongside two generic MPVST Script Host classes that run any script you point them at.

Windows and Linux both ship, each with an editor of its own: a panel built from whatever the instance declares - a patch selector, a bypass switch, a status light and a slider per macro - and your host's generic parameter editor reaches everything either way. The same project renders identical audio on both platforms.

Every instance runs its Python in a separate sidecar process, so a script that loops forever or exhausts memory takes down its own sidecar and gets restarted rather than taking the DAW with it. The audio callback itself stays native and real-time safe.

Install it

Nothing has to be built to use the plug-in - the archives carry everything, including the sidecar engine. There is no published release yet; until there is, scripts/package-linux.sh and scripts/package-windows.sh build the same artifacts into the ignored dist/.

• Windows: run MPVST-<version>-windows-x86_64-setup.exe. It installs for the current user, so there is no UAC prompt. That also decides where the uninstaller shows up: Settings -> Apps -> Installed apps, not the old Control Panel "Programs and Features" list, which is machine-wide installs only. Close your DAW first: a host that has the plug-in loaded holds its files open.
• Linux: unpack MPVST-<version>-linux-x86_64.tar.gz and run the install.sh inside it. It copies the bundle to ~/.vst3; --dir puts it somewhere else and --uninstall removes it.

Then rescan plug-ins in your host - and make it a real rescan, not a restart. A host caches what it found last time against the bundle's contents, and REAPER was observed holding entries from an earlier build after an install (Preferences -> Plug-ins -> VST -> Re-scan clears it). The bundle registers a named plug-in per library instrument and effect, plus the two script hosts; mpvst_scan_plugins.py --list prints the current set.

Use it

Windows and Linux each have a page covering what you just installed: where the bundle went, the editor and its parameters, rescanning after you add a script of your own, and how to point an instance at a file you are editing. The installer puts the one for your platform beside the uninstaller, so it is also there after you install.

Known limitations

• No host-visible diagnostic string. Both editors show only the ready and error parameters; the bounded diagnostic text is available through the transport API.
• The editor is one generic panel. Per-script panels, a shared knob widget, meters, and resizable or zoomable editors are all deferred.
• State embeds one source file, not a dependency bundle. Imports must resolve in the sidecar's own MicroPython environment.
• MPVST_SCRIPT_PATH is process-wide, so two developer-file instances cannot follow different scripts - they re-read it on restart and on save. Projects that need per-instance scripts embed them in state instead, which reaper/matrix/build_effect_project.py demonstrates by synthesizing the chunks directly.
• The 2,080 hidden MIDI parameters are standards-compliant and validator-clean but unprofiled for scan and project-load overhead in real DAWs.
• The installers are not code signed, so Windows SmartScreen warns on first run and macOS is not a target at all.
• The Linux REAPER used for testing runs under WSLg with no audio device. Real-time playback on Linux hardware has not been exercised.
• REAPER is the only DAW tested.

Going further

• Getting started - what MPVST is, installing it, and finding your first instrument in the FX browser.
• Generating projects - building .RPP files programmatically: the state chunk, class IDs, and Reaper's routing traps.
• Writing your own instruments and effects - what a script declares, how macros and patches reach it, what the library gives you to build on. Needs nothing built.
• Working on MPVST itself - repository layout, prerequisites, building the plug-in and the sidecar engine, the test suite, the DAW harnesses, cutting a release.
• What the shipped engine cannot do - no sockets, no SSL, no FFI, and why a plug-in that runs other people's code ships that way.
• Architecture - the shared-memory protocol between plug-in and sidecar, with the editor's half alongside it.

License

MIT, in LICENSE — the same terms as the rest of PyDevices.

That covers this repository's own source. The Steinberg VST3 SDK is not vendored here: scripts/fetch-vst3-sdk.sh clones it into .deps/, which is ignored. It carries its own dual license (GPLv3 or a proprietary Steinberg agreement), and anyone distributing a built plug-in binary has to satisfy one of those two for the SDK it links. Building from source for your own use does not change anything here.