MIDI VST3 Capture Host

A small Windows JUCE host helper for MIDI-producing VST3 plugins. It opens a plugin's editor, optionally feeds it a source MIDI file, captures MIDI events returned by the plugin, and writes a Standard MIDI File.

This is an early prototype, not a general-purpose DAW or a security sandbox. Only use VST3 plugins you trust. A plugin runs in-process and can crash the helper.

Build

The Windows GitHub Actions workflow builds a 64-bit Release executable and uploads it as an artifact. For a local build, install CMake 3.25+ and Visual Studio 2022 C++ tools, then run:

cmake -S . -B build -A x64
cmake --build build --config Release

JUCE 8.0.6 is fetched by CMake at configure time.

Launch configuration

The helper accepts the path to a JSON configuration file as its only argument:

{
  "plugin_path": "C:/Program Files/Common Files/VST3/Example.vst3",
  "input_midi_path": "C:/temp/source.mid",
  "output_midi_path": "C:/temp/captured.mid",
  "status_path": "C:/temp/capture-status.json",
  "duration_seconds": 15,
  "ticks_per_beat": 480,
  "tempo_microseconds": 500000
}

input_midi_path may be an empty string when the plugin generates notes without MIDI input. The plugin editor opens first; configure it, then click Start capture. The helper writes a success or failure result to status_path. It will not write a successful MIDI file unless at least one note-on event was captured.

The prototype feeds MIDI events from the input file in real time and timestamps captured plugin output against the audio callback. It does not yet provide a full DAW transport or isolate plugin crashes.