minihost

Minihost is a headless, JUCE-based audio plugin host that supports VST3, AudioUnit, and LV2 plugins. It provides a C/C++ API for integration and a Python API powered by nanobind.

At a glance

Process an input WAV through a chain of effect plugins and write the result:

import minihost

with (
    minihost.Plugin("/path/to/delay.vst3", sample_rate=48000) as delay,
    minihost.Plugin("/path/to/reverb.vst3", sample_rate=48000) as reverb,
    minihost.PluginChain([delay, reverb]) as chain,
):
    minihost.process_audio_to_file(
        chain, "in.wav", "out.wav",
        tail_seconds=4.0,           # capture reverb tail
    )

process_audio_to_file handles block iteration, latency compensation, sample-rate matching, channel layout, and tail rendering. See the Python API section for lower-level control.

Features

• Load VST3 plugins (macOS, Windows, Linux)

• Load AudioUnit plugins (macOS only)

• Load LV2 plugins (macOS, Windows, Linux)

• Headless mode (default) - no GUI dependencies, uses JUCE's juce_audio_processors_headless module

• Plugin chaining - connect multiple plugins in series (synth -> reverb -> limiter)

• AudioBuffer -- the canonical audio container. Planar float32, JUCE-backed, stdlib-only. Numpy-style 2-axis indexing (buf[ch, frame_slice]), JUCE DSP ops (clear, apply_gain, magnitude, copy), zero-copy channel-range views (buf.channel_view(start, count)), DLPack export so it's accepted directly by Plugin.process / numpy.asarray / PyTorch / etc.

• numpy is optional. pip install minihost installs no Python runtime dependencies; the AudioBuffer API works without numpy. pip install minihost[numpy] enables numpy-typed APIs (AudioBuffer.as_ndarray(), read_audio(as_=numpy.ndarray), accepting numpy arrays as inputs).

• High-level offline processing -- process_audio_to_file(plugin_or_chain, "in.wav", "out.wav") collapses block iteration, latency compensation, sample-rate matching, and tail rendering into one call.

• Audio file I/O via miniaudio + tflac -- read WAV/FLAC/MP3/Vorbis, write WAV (16/24/32-bit) and FLAC (16/24-bit), optional Broadcast Wave (bext) metadata on WAV output (write_audio(..., bwf={...}))

• Sample rate conversion via miniaudio resampler -- minihost.resample() API and minihost resample CLI subcommand

• Real-time audio playback via miniaudio (cross-platform), with duplex capture mode for effect processing

• Audio device selection -- enumerate and target specific playback/capture devices (minihost devices CLI, audio_get_playback_devices() / audio_get_capture_devices() API, --playback-device / --capture-device on minihost play)

• Real-time audio input -- lock-free ring buffer API (write_input()) and duplex capture (capture=True) for routing system audio through effects

• Real-time MIDI I/O via libremidi (cross-platform)

• Control surface mapping -- minihost.MidiMapper translates incoming MIDI CCs from a USB control surface (Launch Control / MIDIMix / nanoKONTROL / X-Touch / etc.) onto plugin parameters with optional value-range and curve (linear/exp/log); CLI: minihost play --map "channel:cc:param[:lo:hi[:curve]]" (repeatable) or --map-file PATH for saved JSON mappings.

• 14-bit MIDI CC -- map_cc14 pairs controller n (0-31) with n+32 for 16384 steps instead of 128, which matters on anything a 7-bit CC makes audibly stepped; CLI: minihost play --map14 "channel:msb_cc:param". Overlap with a plain CC is rejected at map time, because a stray mapping on the LSB otherwise shadows it silently.

• OSC in and out -- OscServer / OscClient over UDP, built on JUCE's juce_osc (no new dependency). AudioDevice.connect_osc(port) parses /mh/param/<index> in C and drives parameters without taking a lock or the GIL; OscMapper adds name addressing, curves and ranges; OscFeedback sends values back so a surface tracks preset loads instead of lying. CLI: minihost play --osc-port 9000 --osc-feedback HOST:PORT.

• Sample-accurate live parameter writes -- AudioDevice.send_param() queues a change on a lock-free ring the audio thread drains at the next block boundary, rather than writing the parameter underneath a running processBlock as set_param does. Coalesces per parameter per block, so a fader drag costs one write.

• Host playhead for realtime -- AudioDevice.set_transport_enabled(True) plus transport_play() / transport_set_bpm() / loop points gives live plugins a tempo and a position. Tempo-synced delays, arpeggiators and LFOs previously saw no transport at all under minihost play.

• Generated touch surfaces -- minihost touch synth.vst3 turns a plugin's parameters into a TouchOSC layout and a matching MIDI map, rendered from one table so the two cannot disagree. Widget choice follows the plugin's metadata (boolean -> button, stepped -> radio, else fader). Generation needs no dependency; compiling to .tosc uses the optional minihost[touch] extra (py2tosc).

• Looped sources for live tweaking -- minihost play --loop-midi PATH loops a MIDI file through the plugin (with All Notes Off between iterations); --loop-audio PATH loops an audio file into the plugin's input ring buffer at real time. Useful for parameter exploration against a repeating pattern.

• Virtual MIDI ports - create named ports that DAWs can connect to (macOS, Linux)

• Standalone MIDI input - monitor raw MIDI messages without a plugin (MidiIn class)

• Batch processing -- glob patterns and directory output for processing multiple files (minihost process -i "*.wav" -o output/)

• Auto-tail detection -- tail_seconds="auto" monitors output amplitude and stops rendering when reverb/delay tails decay below threshold

• Process audio with sample-accurate parameter automation

• Single and double precision processing

• MIDI input/output support

• Transport info for tempo-synced plugins

• State save/restore for presets and per-program state

• Preset morphing -- minihost.morph interpolates between two parameter snapshots (A/B blend) for sound-design sweeps (capture / lerp / apply / morph)

• Thread-safe by design -- construction, destruction, and thread-affine control operations are marshaled onto a dedicated native plugin thread, so a plugin can be built on one thread and used or closed from another (only the real-time process* path is single-thread/lock-free)

• Change notifications (latency, parameter info, program, non-parameter state) with deferred dispatch via poll_callbacks()

• Parameter gestures for automation bracketing

• Bus layout validation and sidechain support

• Track name/color metadata forwarding to plugins

• Latency and tail time reporting

• Parameter access by name -- plugin.find_param("Cutoff"), plugin.get_param_by_name("Cutoff"), plugin.set_param_by_name("Cutoff", 0.5) with case-insensitive lookup

• Async plugin loading -- minihost.open_async() returns a concurrent.futures.Future that resolves to a ready-to-use Plugin, loaded off the calling thread (safe to use/close from any thread thanks to the dedicated plugin thread)

• VST3 preset I/O -- read and write .vstpreset files from C (minihost_vstpreset.h), C++, and Python (minihost.vstpreset); minihost presets CLI subcommand exports the current plugin state, optionally after loading a program, state blob, or another .vstpreset

Library structure

minihost ships as two separate static libraries with a one-way dependency: libminihost_audio builds on libminihost, never the reverse.

• libminihost -- the plugin host core (projects/libminihost/). Loads and runs VST3/AU/LV2 plugins and processes audio blocks you hand it: MIDI in/out, parameters, state save/restore, sample-accurate automation, sidechain, transport, bus layouts, and the routing abstractions (PluginChain, PluginBus, PluginGraph). Depends only on JUCE. C ABI prefix: mh_* (e.g. mh_open, mh_process, mh_chain_*, mh_bus_*, mh_graph_*). Header: minihost.h. Link this alone to load a plugin and feed it your own buffers -- the offline and embedded path, with no device or codec dependencies.

• libminihost_audio -- the I/O layer around the core (projects/libminihost_audio/). It has no plugin-format knowledge; it gets audio and MIDI in and out of the machine and drives a plugin or chain through its real-time audio callback. Provides live audio device playback/capture (miniaudio), audio file read/write (read WAV/FLAC/MP3/Vorbis; write WAV/FLAC via miniaudio + tflac), MIDI ports (libremidi), and the lock-free ring buffers. Depends on libminihost plus the vendored miniaudio, tflac, and libremidi. C ABI prefix: mh_audio_*. Headers: minihost_audio.h, minihost_audiofile.h, minihost_midi.h. Link this in addition to libminihost when you want real-time devices, file I/O, or MIDI hardware.

In short: libminihost runs the plugin; libminihost_audio connects it to speakers, files, and MIDI hardware. The Python wheel links both.

Desktop application

minihost_desktop (projects/minihost_desktop/) is a developer-facing GUI host built on the same libraries. It loads VST3/AU/LV2 plugins, wires them into a node graph on a canvas, opens native plugin editor windows, renders the graph to disk offline, and drives a realtime audio device with live MIDI input and a transport (BPM / loop region). Project files are JSON, schema-versioned, and round-trip with the Python loader (minihost.load_project / render_project), so a graph built in the app renders identically from the command line.

Each plugin window carries the host-side controls a plugin's own editor usually leaves out: a factory-program selector, a bypass toggle (backed by the plugin's own bypass parameter where it publishes one), and .vstpreset load/save for interchange with other hosts. Offline renders put every plugin into non-realtime mode for the duration, so a bounce uses the plugin's offline code path rather than its realtime one.

Status: functional and pre-release. Both the offline renderer and the realtime engine are built and tested. Not yet done: packaging (code signing, notarization, installers). See docs/dev/desktop_app.md for the design and docs/dev/desktop_app_todo.md for per-feature status.

Plugins run in-process, the same trust model a DAW uses: a misbehaving plugin can crash the whole app and lose unsaved canvas edits. Two mitigations bound the harm. Plugin scanning is out-of-process, so a plugin that crashes while being catalogued takes down only a disposable child. And the working project is autosaved to a sidecar every few seconds; after an unclean exit the app offers to recover it on the next launch, so a crash costs at most a few seconds of unsaved editing. Save often regardless.

The app is opt-in and off by default (it requires a non-headless build, so it is excluded from the headless library, CLI, and Python wheel builds):

# Build the desktop app into its own build-desktop/ dir (keeps the
# headless library / CLI / wheel build in build/ untouched)
make desktop

# Or configure it by hand:
cmake -B build-desktop -DMINIHOST_BUILD_DESKTOP=ON
cmake --build build-desktop --config Release --target minihost_desktop

# Build (if needed) and launch it (macOS)
make run-desktop

Headless entry points for scripting and CI: minihost_desktop --render-project=<project.json> renders a project with no window, and minihost_desktop --save-roundtrip=<project.json> parses and re-saves a project (used as a build smoke test).

Requirements

• CMake 3.20+

• C++17 compiler

• JUCE framework (automatically downloaded if not present)

• Vendored C libraries: miniaudio, tflac, libremidi, midifile (see docs/vendored.md)

Platform-specific

• macOS: Xcode command line tools

• Windows: Visual Studio 2019+ or MinGW

• Linux: Install the following development libraries:

  sudo apt install libasound2-dev libfreetype-dev libfontconfig1-dev \
      libwebkit2gtk-4.1-dev libgtk-3-dev libgl-dev libcurl4-openssl-dev
  

Building

macOS / Linux

# Clone the repository
git clone https://github.com/shakfu/minihost.git
cd minihost

# Build (JUCE will be downloaded automatically)
make

# Or with a custom JUCE path
cmake -B build -DJUCE_PATH=/path/to/JUCE
cmake --build build

# Also build the non-headless libminihost_gui.a (GUI support: plugin
# editor windows). The headless libminihost.a is still built alongside it.
cmake -B build -DMINIHOST_BUILD_GUI_LIB=ON
cmake --build build

Windows

# Clone the repository
git clone https://github.com/shakfu/minihost.git
cd minihost

# Download JUCE
python scripts/download_juce.py

# Configure and build
cmake -B build
cmake --build build --config Release

JUCE Setup

JUCE is downloaded automatically by make (macOS/Linux). You can also download it manually:

python scripts/download_juce.py

To use a different version or existing installation:

# Download specific version (macOS/Linux)
JUCE_VERSION=8.0.6 python scripts/download_juce.py

# Download specific version (Windows PowerShell)
$env:JUCE_VERSION="8.0.6"; python scripts/download_juce.py

# Or point to existing JUCE
cmake -B build -DJUCE_PATH=/path/to/your/JUCE

Command Line Interface

The minihost command provides a CLI for common plugin operations:

# Install (from source)
uv sync

# Available commands
minihost --help
usage: minihost [-h] [-r SAMPLE_RATE] [-b BLOCK_SIZE]
                {scan,info,params,midi,devices,presets,play,process,resample} ...

Audio plugin hosting CLI

positional arguments:
  {scan,info,params,midi,devices,presets,play,process,resample}
                        Commands
    scan                Scan directory for plugins
    info                Show plugin info
    params              List plugin parameters
    midi                List or monitor MIDI ports
    devices             List audio playback/capture devices
    presets             List factory presets or export .vstpreset files
    play                Play plugin with real-time audio/MIDI
    process             Process audio through plugin (offline)
    resample            Resample audio file to a different sample rate

options:
  -h, --help            show this help message and exit
  -r, --sample-rate SAMPLE_RATE
                        Sample rate in Hz (default: 48000)
  -b, --block-size BLOCK_SIZE
                        Block size in samples (default: 512)

Commands

minihost info - Show plugin info

minihost info /path/to/plugin.vst3          # full info (loads plugin)
minihost info /path/to/plugin.vst3 --probe  # lightweight metadata only
minihost info /path/to/plugin.vst3 --json   # JSON output

By default shows full runtime details (sample rate, channels, latency, buses, presets). Use --probe for fast metadata-only mode without fully loading the plugin.

minihost scan - Scan directory for plugins

minihost scan /Library/Audio/Plug-Ins/VST3/
minihost scan ~/Music/Plugins --json

minihost params - List plugin parameters

minihost params /path/to/plugin.vst3
minihost params /path/to/plugin.vst3 --json

minihost devices - List audio devices

minihost devices                    # list playback and capture devices
minihost devices --json             # JSON output

Use an index or case-insensitive device-name substring with minihost play --playback-device / --capture-device.

minihost presets - List or export factory presets

# List factory presets
minihost presets /path/to/synth.vst3
minihost presets /path/to/synth.vst3 --json

# Export factory preset N as a .vstpreset
minihost presets /path/to/synth.vst3 --program 5 --save preset5.vstpreset

# Round-trip: load a .vstpreset and re-save (preserves class_id)
minihost presets /path/to/synth.vst3 --load-vstpreset in.vstpreset --save out.vstpreset

# Convert a raw state blob to .vstpreset
minihost presets /path/to/synth.vst3 --state state.bin --save out.vstpreset

minihost midi - List or monitor MIDI ports

minihost midi                          # list all MIDI ports
minihost midi --json                   # list as JSON
minihost midi -m 0                     # monitor MIDI input port 0
minihost midi --virtual-midi "Monitor" # create virtual port and monitor

minihost play - Play plugin with real-time audio/MIDI

# Connect to MIDI input port 0
minihost play /path/to/synth.vst3 --midi 0

# Create a virtual MIDI port (macOS/Linux)
minihost play /path/to/synth.vst3 --virtual-midi "My Synth"

# Enable audio input for effect processing (duplex mode)
minihost play /path/to/reverb.vst3 --input
minihost play /path/to/amp-sim.vst3 --input --midi 0  # with MIDI too

# Select specific audio devices (index from `minihost devices` or name substring)
minihost play /path/to/synth.vst3 --playback-device "BlackHole"
minihost play /path/to/effect.vst3 --input --playback-device 0 --capture-device 1

Map a control surface to plugin parameters

--map wires incoming MIDI CCs from a USB control surface (Launch Control, MIDIMix, nanoKONTROL, X-Touch, etc.) onto plugin parameters. When set, MIDI is routed through Python via a MidiMapper; mapped CCs become parameter writes and unmapped events (notes, unmapped CCs) are forwarded to the plugin so notes still play. Format: channel:cc:param[:lo:hi[:curve]]. Curves: linear (default), exp (more resolution at low end), log (more resolution at high end).

# One mapping per --map flag, repeatable
minihost play /path/to/synth.vst3 --midi 0 \
  --map 0:7:Volume \
  --map 0:10:Pan:-1:1 \
  --map 0:74:Cutoff:0:1:exp

For a permanent setup, save the mappings to a JSON file once and load it with --map-file:

{
  "mappings": [
    {"channel": 0, "cc": 7,  "param": "Volume"},
    {"channel": 0, "cc": 10, "param": "Pan", "value_range": [-1.0, 1.0]},
    {"channel": 0, "cc": 74, "param": "Cutoff", "curve": "exp"}
  ]
}

minihost play /path/to/synth.vst3 --midi 0 \
  --map-file ~/.config/minihost/launch_control.json

--map and --map-file are combinable -- the file loads first, CLI args append. Required JSON fields per entry: channel, cc, param. Optional: value_range (default [0.0, 1.0]), curve (default "linear").

Loop a MIDI or audio file as the source

--loop-midi loops a MIDI file into a synth (or any plugin that accepts MIDI), useful for live-tweaking parameters against a repeating pattern. A Python thread schedules events at wall-clock-correct times; All Notes Off is sent on every channel between iterations to silence sustained notes.

# Loop a MIDI pattern through a synth while live-tweaking knobs
minihost play /path/to/synth.vst3 \
  --midi 0 \
  --map 0:74:Cutoff:0:1:exp \
  --loop-midi tests/_wav/test_pattern.mid

--loop-audio loops an audio file as the plugin's input, useful for testing effects against a known source without needing live audio. The ring buffer is auto-enabled; the file is resampled to the device rate if needed. Mutually exclusive with --input.

# Loop a guitar take into a reverb while turning the mix knob
minihost play /path/to/reverb.vst3 \
  --midi 0 \
  --map 0:7:Mix \
  --loop-audio guitar_dry.wav

Both loop flags can run alongside live MIDI input (the file's events and your live notes are merged into the plugin).

minihost process - Process audio/MIDI offline

# Process audio through effect
minihost process /path/to/effect.vst3 -i input.wav -o output.wav

# With parameter control
minihost process /path/to/effect.vst3 -i input.wav -o output.wav --param "Mix:0.5"

# Render MIDI through synth
minihost process /path/to/synth.vst3 -m song.mid -o output.wav --tail 3.0

# With preset and bit depth
minihost process /path/to/synth.vst3 -m song.mid -o output.wav --preset 5 --bit-depth 16

# Sidechain processing (second -i is sidechain)
minihost process /path/to/compressor.vst3 -i main.wav -i sidechain.wav -o output.wav

# Batch processing (glob input, directory output)
minihost process /path/to/reverb.vst3 -i "drums/*.wav" -o processed/
minihost process /path/to/effect.vst3 -i "*.wav" -o output/ -y  # overwrite existing

# Mixed sample rates are automatically resampled (use --no-resample to error instead)
minihost process /path/to/effect.vst3 -i 44100hz.wav -i 48000hz_sidechain.wav -o out.wav

minihost resample - Resample audio files

minihost resample input.wav -o output.wav -r 48000
minihost resample input.wav -o output.wav -r 44100 --bit-depth 16
minihost resample input.wav -o output.wav -r 96000 -y  # overwrite

Global Options

Option	Description
-r, --sample-rate	Sample rate in Hz (default: 48000)
-b, --block-size	Block size in samples (default: 512)

Native CLI binaries

Alongside the Python minihost command, the project ships two native binaries -- minihost_c (pure C) and minihost_cpp (C++) -- built into build/projects/ and published in the cli release archive. They are independent implementations over the same C API and are meant to be interchangeable; a conformance test runs them against each other and fails if they diverge. Beyond the single-plugin commands they add the routing ones:

Plugins are named by path, or by name once they have been scanned -- matching ignores case and takes the whole name:

minihost_c scan                    # index this platform's plugin locations
minihost_c probe dexed             # by name (whole name, any case)
minihost_c --fuzzy probe "pro-q 3" # --fuzzy to match part of a name
minihost_c --format au probe "FabFilter Pro-Q 4"   # pin a format

A plugin installed in both AU and VST3 resolves to the VST3 unless --format says otherwise. Substring matching is opt-in because it is rarely decisive on a large collection: with 343 plugins installed here, reverb matches 5 and filter 31.

scan takes an optional directory to scan instead of the defaults. It probes each plugin, so a first pass over a large collection takes minutes; results are cached (shared with the Python CLI's cache), written as the scan proceeds, and only changed plugins are re-probed. Each plugin is probed in a child process the scan is willing to lose, so one that hangs or crashes on load costs one cache entry (timeout / crash) instead of the scan -- --in-process opts out. See the CLI reference.

# one plugin: audio in, or a MIDI file through an instrument
minihost_c process Plugin.vst3 -i input.wav -o output.wav --tail 3
minihost_c process Synth.vst3  -m song.mid  -o output.wav --tail 2

# plugins in series; MIDI effects come first and drive what follows
minihost_c chain EQ.vst3 Reverb.vst3 -i input.wav -o output.wav --mix 1:0.5 --tail 3
minihost_c chain Arpeggiator.component Synth.vst3 -m song.mid -o output.wav

# branches in parallel, summed -- one MIDI part layered across instruments.
# A branch may itself be a chain: commas run plugins in series.
minihost_c bus SynthA.vst3 SynthB.vst3 -m song.mid -o output.wav
minihost_c bus Synth.vst3 "Chorder.component,Synth.vst3" -m song.mid -o out.wav --gain 1:0.7

See the CLI reference for the full option list and MIDI Routing for why MIDI effects must precede the instrument they drive.

Python API

Install:

pip install minihost              # AudioBuffer-only API; no numpy required
pip install minihost[numpy]       # adds numpy-typed return values + numpy input acceptance

The default audio container is minihost.AudioBuffer (planar float32, JUCE-backed, stdlib-only). It supports DLPack so any C extension that takes a 2D float32 c-contiguous buffer (including all of minihost's process methods) accepts it directly. Numpy is fully supported when installed -- pass as_=numpy.ndarray to receive numpy arrays from read_audio / render_midi, or call .as_ndarray() on any AudioBuffer for a zero-copy numpy view.

Quick start: process a WAV file through a chain

import minihost

with (
    minihost.Plugin("/path/to/delay.vst3", sample_rate=48000) as delay,
    minihost.Plugin("/path/to/reverb.vst3", sample_rate=48000) as reverb,
    minihost.PluginChain([delay, reverb]) as chain,
):
    minihost.process_audio_to_file(
        chain, "in.wav", "out.wav",
        tail_seconds=4.0,           # capture reverb tail
    )

process_audio_to_file handles block iteration, latency compensation, sample-rate matching (input is auto-resampled to the plugin's rate), mono-to-stereo channel duplication, and tail rendering. For in-memory data use process_audio(plugin_or_chain, audio, tail_seconds=...), which returns an AudioBuffer.

Lower-level processing

import minihost

plugin = minihost.Plugin("/path/to/plugin.vst3", sample_rate=48000)

# AudioBuffer is the default container. process accepts it directly via DLPack.
input_audio = minihost.AudioBuffer(2, 512)
output_audio = minihost.AudioBuffer(2, 512)
plugin.process(input_audio, output_audio)

# Numpy users can mix and match -- both accepted as inputs:
import numpy as np                                       # requires minihost[numpy]
input_np = np.zeros((2, 512), dtype=np.float32)
plugin.process(input_np, output_audio)                   # numpy in -> AudioBuffer out
output_np = output_audio.as_ndarray()                    # zero-copy numpy view

Parameter Access by Name

import minihost

plugin = minihost.Plugin("/path/to/synth.vst3", sample_rate=48000)

# Find parameter index by name (case-insensitive)
idx = plugin.find_param("Cutoff")

# Get/set by name directly
value = plugin.get_param_by_name("Cutoff")
plugin.set_param_by_name("Cutoff", 0.7)
plugin.set_param_by_name("resonance", 0.4)  # case-insensitive

# Index-based API remains available for hot paths
plugin.set_param(idx, 0.5)

Preset Morphing

Interpolate between two parameter snapshots (an A/B blend), useful for sound-design sweeps. Morphing operates on normalized per-parameter values (not opaque VST/AU state blobs).

import minihost

plugin = minihost.Plugin("/path/to/synth.vst3", sample_rate=48000)

# Capture two states (e.g. after loading two presets)
a = minihost.capture_params(plugin)
# ... dial in a different sound ...
b = minihost.capture_params(plugin)

# Blend 30% of the way from A to B and apply to the plugin
minihost.morph_params(plugin, a, b, 0.3)

# Or compute a blend without applying; t can be a per-parameter sequence
blended = minihost.lerp_params(a, b, 0.5)
minihost.apply_params(plugin, blended)

Async Plugin Loading

import minihost

# Load a heavy plugin in the background (off the calling thread)
future = minihost.open_async("/path/to/heavy_sampler.vst3", sample_rate=48000)

# Do other work while plugin loads...

# Block until ready -- returns a normal Plugin
plugin = future.result()
print(f"Loaded: {plugin.num_params} params")

# The plugin is built on a loader thread but is safe to use and close from
# any thread: minihost marshals thread-affine operations onto a dedicated
# native plugin thread. Loads are serialized on that thread, so this is
# non-blocking (not parallel) loading.
plugin.close()

Shared session for multi-plugin loading

mh_open and its Python equivalent register the JUCE plugin formats on every call. A Session builds that format manager once and reuses it across loads, probes and scans, which is the difference between loading one plugin and loading a chain of them.

import minihost

session = minihost.Session()
eq     = session.open("/path/to/EQ.vst3", sample_rate=48000)
reverb = session.open("/path/to/Reverb.vst3", sample_rate=48000)

# AudioUnits are identified by an id rather than a path, so they load from a
# serialized PluginDescription -- through the session like anything else.
delay = session.open_desc(
    '<PLUGIN name="AUDelay" format="AudioUnit" file="AudioUnit:Effects/aufx,dely,appl"/>'
)

session.close()   # the plugins keep working; they do not depend on it

The native chain and bus commands load this way, which is where the saving shows: a four-plugin chain built four format managers before.

Audio Device Enumeration and Selection

import minihost

# List available audio devices
for dev in minihost.audio_get_playback_devices():
    print(f"[{dev['index']}] {dev['name']}{' *' if dev['is_default'] else ''}")

for dev in minihost.audio_get_capture_devices():
    print(f"[{dev['index']}] {dev['name']}{' *' if dev['is_default'] else ''}")

# Target a specific playback device (e.g., for routing to a loopback driver)
plugin = minihost.Plugin("/path/to/synth.vst3", sample_rate=48000)
with minihost.AudioDevice(plugin, playback_device_index=2) as audio:
    audio.send_midi(0x90, 60, 100)

# Duplex mode with explicit capture + playback devices
with minihost.AudioDevice(plugin, capture=True,
                          capture_device_index=1,
                          playback_device_index=0) as audio:
    pass

Pass -1 (the default) to use the system default device.

Real-time Audio Playback

import minihost
import time

plugin = minihost.Plugin("/path/to/synth.vst3", sample_rate=48000)

# Use as context manager for automatic start/stop
with minihost.AudioDevice(plugin) as audio:
    # Plugin is now producing audio through speakers
    # Send MIDI programmatically
    audio.send_midi(0x90, 60, 100)  # Note on: C4, velocity 100
    time.sleep(1)
    audio.send_midi(0x80, 60, 0)    # Note off
    time.sleep(0.5)

# Or manual control
audio = minihost.AudioDevice(plugin)
audio.start()
audio.send_midi(0x90, 64, 80)  # E4 note on
time.sleep(0.5)
audio.send_midi(0x80, 64, 0)   # E4 note off
audio.stop()

Real-time Audio Input (Effect Processing)

Route system audio through an effect plugin using duplex mode or the ring buffer API:

import minihost
import time

plugin = minihost.Plugin("/path/to/reverb.vst3", sample_rate=48000)

# Option 1: Duplex mode (system audio capture -> plugin -> speakers)
with minihost.AudioDevice(plugin, capture=True) as audio:
    print("Processing system audio through effect... Ctrl+C to stop")
    time.sleep(10)

# Option 2: Ring buffer (push audio from Python).
# AudioBuffer slicing returns a new AudioBuffer; write_input accepts it
# directly via DLPack -- no numpy required.
audio = minihost.AudioDevice(plugin)
audio.enable_input()  # ~0.5s ring buffer by default
audio.start()

data, sr = minihost.read_audio("guitar.wav")
block_size = 512
for i in range(0, data.frames, block_size):
    chunk = data[:, i:i+block_size]
    audio.write_input(chunk)
    time.sleep(block_size / sr * 0.9)  # pace to real time

audio.stop()
audio.disable_input()

Real-time MIDI I/O

import minihost

# Enumerate available MIDI ports
inputs = minihost.midi_get_input_ports()
outputs = minihost.midi_get_output_ports()
print(f"MIDI Inputs: {inputs}")
print(f"MIDI Outputs: {outputs}")

# Connect MIDI when creating AudioDevice
with minihost.AudioDevice(plugin, midi_input_port=0) as audio:
    # MIDI from port 0 is now routed to the plugin
    pass

# Or connect dynamically
audio = minihost.AudioDevice(plugin)
audio.connect_midi_input(0)
audio.start()
# ...
audio.disconnect_midi_input()
audio.stop()

# Create virtual MIDI ports (appear in system MIDI, DAWs can connect)
audio = minihost.AudioDevice(plugin)
audio.create_virtual_midi_input("minihost Input")
audio.create_virtual_midi_output("minihost Output")
audio.start()
# Other apps can now send MIDI to "minihost Input"
# and receive MIDI from "minihost Output"

Standalone MIDI Input

Monitor MIDI messages without loading a plugin:

import minihost

def on_midi(data: bytes):
    status = data[0]
    if status & 0xF0 == 0x90 and data[2] > 0:
        print(f"Note On: {data[1]} vel={data[2]}")

# Open hardware MIDI port
with minihost.MidiIn.open(0, on_midi) as midi_in:
    input("Press Enter to stop...\n")

# Or create a virtual MIDI port
with minihost.MidiIn.open_virtual("My Monitor", on_midi) as midi_in:
    input("Press Enter to stop...\n")

Audio File I/O

import minihost

# Read audio files (WAV, FLAC, MP3, Vorbis).
# Default container is AudioBuffer (planar float32, no numpy required).
data, sample_rate = minihost.read_audio("input.wav")
# data is an AudioBuffer of shape (channels, samples)

# Pass as_=numpy.ndarray to get a numpy array instead (requires minihost[numpy]).
import numpy as np
data_np, sample_rate = minihost.read_audio("input.wav", as_=np.ndarray)

# write_audio accepts AudioBuffer, numpy ndarray, or any DLPack/buffer-protocol producer.
minihost.write_audio("output.wav", data, sample_rate, bit_depth=24)   # WAV (16/24/32-bit)
minihost.write_audio("output.flac", data, sample_rate, bit_depth=24)  # FLAC (16/24-bit)

# Broadcast Wave (bext) metadata for film/broadcast workflows (WAV only)
minihost.write_audio("take.wav", data, sample_rate, bit_depth=24, bwf={
    "description": "Scene 12 take 3",
    "originator": "minihost",
    "originator_reference": "REF-0012",
    "origination_date": "2026-07-07",   # yyyy-mm-dd
    "origination_time": "12:34:56",     # hh:mm:ss
    "time_reference": 48000 * 3600,     # samples since midnight (timecode anchor)
})

# Get file info without decoding
info = minihost.get_audio_info("song.wav")
print(f"{info['channels']}ch, {info['sample_rate']}Hz, {info['duration']:.2f}s")

Sample Rate Conversion

import minihost

# Works on AudioBuffer (default), numpy ndarray, or any 2D float32
# c-contig buffer-protocol producer. Return type matches the input type
# (AudioBuffer in -> AudioBuffer out; numpy in -> numpy out).
data, sr = minihost.read_audio("input_44100.wav")  # AudioBuffer @ 44.1kHz
resampled = minihost.resample(data, 44100, 48000)   # -> 48kHz AudioBuffer
minihost.write_audio("output_48000.wav", resampled, 48000)

MIDI File Read/Write

import minihost

# Create a new MIDI file
mf = minihost.MidiFile()
mf.ticks_per_quarter = 480

# Add events
mf.add_tempo(0, 0, 120.0)  # 120 BPM at tick 0
mf.add_note_on(0, 0, 0, 60, 100)    # C4 note on at tick 0
mf.add_note_off(0, 480, 0, 60, 0)   # C4 note off at tick 480

# Save to file
mf.save("output.mid")

# Load existing MIDI file
mf2 = minihost.MidiFile()
mf2.load("input.mid")

# Read events
events = mf2.get_events(0)  # Get events from track 0
for event in events:
    if event['type'] == 'note_on':
        print(f"Note {event['pitch']} vel {event['velocity']} at {event['seconds']:.2f}s")

MIDI File Rendering

Render MIDI files through plugins to produce audio output. Returns AudioBuffer by default; pass as_=numpy.ndarray for numpy:

import minihost

plugin = minihost.Plugin("/path/to/synth.vst3", sample_rate=48000)

# Render to AudioBuffer (default)
audio = minihost.render_midi(plugin, "song.mid")
print(f"Rendered {audio.frames / 48000:.2f} seconds of audio")

# Numpy variant
import numpy as np
audio_np = minihost.render_midi(plugin, "song.mid", as_=np.ndarray)

# Render directly to WAV file (returns frame count)
samples = minihost.render_midi_to_file(plugin, "song.mid", "output.wav", bit_depth=24)

# Stream blocks for large files or real-time processing.
# Each yielded block is an AudioBuffer; pass as_=numpy.ndarray to yield numpy instead.
for block in minihost.render_midi_stream(plugin, "song.mid", block_size=512):
    # block.shape == (channels, n) where n <= block_size
    pass

# Auto-detect reverb/delay tail (stops when output decays below -80 dB)
audio = minihost.render_midi(plugin, "song.mid", tail_seconds="auto")

# Custom threshold (-40 dB) and max tail (10s safety cap)
audio = minihost.render_midi(plugin, "song.mid",
                             tail_seconds="auto", tail_threshold=1e-2, max_tail_seconds=10)

# Fine-grained control with MidiRenderer class
renderer = minihost.MidiRenderer(plugin, "song.mid")
print(f"Duration: {renderer.duration_seconds:.2f}s")

while not renderer.is_finished:
    block = renderer.render_block()   # returns AudioBuffer or None
    print(f"Progress: {renderer.progress:.1%}")

Plugin Chaining

Chain multiple plugins together for serial processing:

import minihost
import time

# Load plugins (all must have same sample rate)
synth = minihost.Plugin("/path/to/synth.vst3", sample_rate=48000)
reverb = minihost.Plugin("/path/to/reverb.vst3", sample_rate=48000)
limiter = minihost.Plugin("/path/to/limiter.vst3", sample_rate=48000)

# Create chain
chain = minihost.PluginChain([synth, reverb, limiter])
print(f"Total latency: {chain.latency_samples} samples")
print(f"Tail length: {chain.tail_seconds:.2f} seconds")

# Real-time playback through chain
with minihost.AudioDevice(chain) as audio:
    audio.send_midi(0x90, 60, 100)  # Note on to synth
    time.sleep(2)
    audio.send_midi(0x80, 60, 0)    # Note off
    time.sleep(1)  # Let reverb tail fade

# Offline processing -- AudioBuffer is the default container
input_audio = minihost.AudioBuffer(2, 512)
output_audio = minihost.AudioBuffer(2, 512)
chain.process(input_audio, output_audio)

# Process with MIDI (enters the first plugin that accepts it, then
# carried on by any plugin that produces MIDI -- e.g. arpeggiator -> synth)
midi_events = [(0, 0x90, 60, 100)]
chain.process_midi(input_audio, output_audio, midi_events)

# Sample-accurate automation across chain
# param_changes: (sample_offset, plugin_index, param_index, value)
param_changes = [
    (0, 1, 0, 0.3),    # Set reverb param 0 at sample 0
    (256, 1, 0, 0.6),  # Change reverb param 0 at sample 256
    (0, 2, 0, 0.8),    # Set limiter param 0 at sample 0
]
chain.process_auto(input_audio, output_audio, midi_events, param_changes)

# Render MIDI file through chain
audio = minihost.render_midi(chain, "song.mid")        # -> AudioBuffer
minihost.render_midi_to_file(chain, "song.mid", "output.wav")

# File-to-file processing through the chain (handles tail, latency, resample)
minihost.process_audio_to_file(chain, "input.wav", "output.wav", tail_seconds=4.0)

# Access individual plugins in chain
for i in range(chain.num_plugins):
    plugin = chain.get_plugin(i)
    print(f"Plugin {i}: {plugin.num_params} params")

Parallel routing (PluginBus)

PluginChain is series; PluginBus is parallel. A bus fans the same input to N branches (each a PluginChain) and sums their outputs with a per-branch gain -- parallel compression, dry-bus + reverb-send, multi-band processing. With process_midi, the same MIDI is delivered to every branch, which is the idiomatic way to layer one part across several instruments:

import minihost

# Three synths layered under one MIDI part, summed to stereo.
a = minihost.PluginChain([minihost.Plugin("/path/to/saw.vst3", sample_rate=48000)])
b = minihost.PluginChain([minihost.Plugin("/path/to/sub.vst3", sample_rate=48000)])
c = minihost.PluginChain([minihost.Plugin("/path/to/pad.vst3", sample_rate=48000)])

bus = minihost.PluginBus(2, 2, max_block_size=512, sample_rate=48000.0)
bus.add_branch(a, gain=1.0)
bus.add_branch(b, gain=0.7)
bus.add_branch(c, gain=0.5)

silence = minihost.AudioBuffer(2, 512)   # synths ignore audio input
out = minihost.AudioBuffer(2, 512)
note_on = [(0, 0x90, 60, 100)]           # C4 reaches ALL three synths
bus.process_midi(silence, out, note_on)

A complete, runnable version (block loop, chord, WAV output) is in examples/parallel_bus.py.

For arbitrary node-to-node topologies (multiple inputs/outputs, MIDI processors, channel pick/merge), use PluginGraph -- the general DAG executor that also backs project files (minihost.load_project). Branch MIDI output is not collected by the bus; reach for PluginGraph if you need that.

VST3 Presets

Read, load, and write Steinberg .vstpreset files:

import minihost
from minihost import vstpreset

plugin = minihost.Plugin("/path/to/synth.vst3")

# Read a .vstpreset into raw chunks
preset = vstpreset.read_vstpreset("patch.vstpreset")
print(preset.class_id, len(preset.component_state or b""))

# Load into a plugin (calls plugin.set_state under the hood)
vstpreset.load_vstpreset("patch.vstpreset", plugin)

# Save the plugin's current state to a .vstpreset.
# class_id defaults to the FUID auto-detected from the plugin bundle's
# moduleinfo.json (requires VST3 SDK 3.7.5+, which all modern plugins ship).
vstpreset.save_vstpreset("out.vstpreset", plugin)

# Or pass class_id explicitly (e.g., for legacy plugins without moduleinfo.json):
vstpreset.save_vstpreset("out.vstpreset", plugin,
                         class_id="ABCDEF0123456789ABCDEF0123456789")

# Read just the class ID from a bundle without instantiating the plugin
fuid = vstpreset.read_class_id_from_bundle("/path/to/synth.vst3")
print(fuid)  # e.g., "ABCDEF0123456789ABCDEF0123456789"

# Or write raw chunks you already have
vstpreset.write_vstpreset("out.vstpreset",
                          class_id=fuid,
                          component_state=plugin.get_state())

C API Usage

#include "minihost.h"

// Load a plugin
char err[256];
MH_Plugin* plugin = mh_open("/path/to/plugin.vst3",
                            48000.0,  // sample rate
                            512,      // max block size
                            2, 2,     // in/out channels
                            err, sizeof(err));

// Process audio
float* inputs[2] = { in_left, in_right };
float* outputs[2] = { out_left, out_right };
mh_process(plugin, inputs, outputs, 512);

// Process with MIDI
MH_MidiEvent midi[] = {
    { 0, 0x90, 60, 100 },   // Note on at sample 0
    { 256, 0x80, 60, 0 }    // Note off at sample 256
};
mh_process_midi(plugin, inputs, outputs, 512, midi, 2);

// Parameter control
int num_params = mh_get_num_params(plugin);
float value = mh_get_param(plugin, 0);
mh_set_param(plugin, 0, 0.5f);

// State save/restore
int size = mh_get_state_size(plugin);
void* state = malloc(size);
mh_get_state(plugin, state, size);
mh_set_state(plugin, state, size);

// Cleanup
mh_close(plugin);

Real-time Audio Playback

#include "minihost_audio.h"

// Enumerate and select a playback device (optional)
MH_AudioDeviceInfo devices[32];
int n = mh_audio_enumerate_playback_devices(devices, 32);
for (int i = 0; i < n; i++) {
    printf("[%d]%s %s\n", i, devices[i].is_default ? "*" : " ", devices[i].name);
}

// Open audio device for real-time playback
MH_AudioConfig config = {
    .sample_rate = 48000,
    .buffer_frames = 512,
    .playback_device_index = -1,  // -1 = system default
    .capture_device_index = -1,
};
MH_AudioDevice* audio = mh_audio_open(plugin, &config, err, sizeof(err));

// Start playback
mh_audio_start(audio);

// Plugin is now producing audio through speakers
// Send MIDI, adjust parameters, etc.

// Stop and cleanup
mh_audio_stop(audio);
mh_audio_close(audio);
mh_close(plugin);

Real-time MIDI I/O

#include "minihost_midi.h"

// Enumerate available MIDI ports
int num_inputs = mh_midi_get_num_inputs();
int num_outputs = mh_midi_get_num_outputs();

for (int i = 0; i < num_inputs; i++) {
    char name[256];
    mh_midi_get_input_name(i, name, sizeof(name));
    printf("MIDI Input %d: %s\n", i, name);
}

// Connect MIDI to audio device
MH_AudioConfig config = {
    .sample_rate = 48000,
    .midi_input_port = 0,   // Connect to first MIDI input
    .midi_output_port = -1  // No MIDI output
};
MH_AudioDevice* audio = mh_audio_open(plugin, &config, err, sizeof(err));

// Or connect/disconnect dynamically
mh_audio_connect_midi_input(audio, 1);
mh_audio_disconnect_midi_input(audio);

// Create virtual MIDI ports (appear in system MIDI, DAWs can connect)
mh_audio_create_virtual_midi_input(audio, "minihost Input");
mh_audio_create_virtual_midi_output(audio, "minihost Output");

Plugin Chaining

Chain multiple plugins together for processing (e.g., synth -> reverb -> limiter):

#include "minihost_chain.h"

// Load plugins
MH_Plugin* synth = mh_open("/path/to/synth.vst3", 48000, 512, 0, 2, err, sizeof(err));
MH_Plugin* reverb = mh_open("/path/to/reverb.vst3", 48000, 512, 2, 2, err, sizeof(err));
MH_Plugin* limiter = mh_open("/path/to/limiter.vst3", 48000, 512, 2, 2, err, sizeof(err));

// Create chain (all plugins must have same sample rate)
MH_Plugin* plugins[] = { synth, reverb, limiter };
MH_PluginChain* chain = mh_chain_create(plugins, 3, err, sizeof(err));

// Get combined latency
int latency = mh_chain_get_latency_samples(chain);

// Process audio through chain
float* inputs[2] = { in_left, in_right };
float* outputs[2] = { out_left, out_right };
mh_chain_process(chain, inputs, outputs, 512);

// Process with MIDI (carried onward by plugins that produce MIDI)
MH_MidiEvent midi[] = { { 0, 0x90, 60, 100 } };
mh_chain_process_midi_io(chain, inputs, outputs, 512, midi, 1, NULL, 0, NULL);

// Sample-accurate automation across chain
MH_ChainParamChange changes[] = {
    { .sample_offset = 0,   .plugin_index = 1, .param_index = 0, .value = 0.3f },
    { .sample_offset = 256, .plugin_index = 1, .param_index = 0, .value = 0.6f },
};
mh_chain_process_auto(chain, inputs, outputs, 512,
                       NULL, 0, NULL, 0, NULL, changes, 2);

// Real-time playback through chain
MH_AudioConfig config = { .sample_rate = 48000, .buffer_frames = 512 };
MH_AudioDevice* audio = mh_audio_open_chain(chain, &config, err, sizeof(err));
mh_audio_start(audio);
// ...
mh_audio_stop(audio);
mh_audio_close(audio);

// Cleanup
mh_chain_close(chain);  // Does not close individual plugins
mh_close(synth);
mh_close(reverb);
mh_close(limiter);

MIDI File Rendering

Read a standard MIDI file into the event form mh_process* consumes. Tracks are merged and the file's tempo map is applied; sample_offset is absolute, so rebase it per block:

MH_MidiEvent* events = NULL;
int count = 0;
double duration = 0.0;
char err[512] = {0};

if (!mh_midi_file_load("song.mid", 48000.0, &events, &count, &duration,
                       err, sizeof(err))) {
    fprintf(stderr, "%s\n", err);
    return 1;
}

int cursor = 0;
for (int start = 0; start < total_frames; start += block) {
    int end = start + block;
    MH_MidiEvent block_midi[256];
    int n = 0;
    while (cursor < count && events[cursor].sample_offset < end && n < 256) {
        block_midi[n] = events[cursor];
        block_midi[n].sample_offset -= start;   // rebase to this block
        n++;
        cursor++;
    }
    mh_process_midi(synth, inputs, outputs, block, block_midi, n);
}

mh_midi_file_free(events);

Audio File I/O

Read and write audio files without external dependencies:

#include "minihost_audiofile.h"

// Read any supported format (WAV, FLAC, MP3, Vorbis)
char err[1024];
MH_AudioData* audio = mh_audio_read("input.flac", err, sizeof(err));
if (audio) {
    printf("Channels: %u, Frames: %u, Rate: %u\n",
           audio->channels, audio->frames, audio->sample_rate);
    // audio->data is interleaved float32
    mh_audio_data_free(audio);
}

// Write audio file (format selected by extension)
mh_audio_write("output.wav", interleaved_data,
               2, num_frames, 48000, 24, err, sizeof(err));   // WAV
mh_audio_write("output.flac", interleaved_data,
               2, num_frames, 48000, 24, err, sizeof(err));   // FLAC

// Get file info without decoding
MH_AudioFileInfo info;
mh_audio_get_file_info("song.wav", &info, err, sizeof(err));
printf("Duration: %.2f seconds\n", info.duration);

// Resample audio (e.g., 44.1kHz -> 48kHz)
MH_AudioData* resampled = mh_audio_resample(
    audio->data, audio->channels, audio->frames,
    44100, 48000, err, sizeof(err));
if (resampled) {
    printf("Resampled: %u frames at %u Hz\n", resampled->frames, resampled->sample_rate);
    mh_audio_data_free(resampled);
}

VST3 Preset I/O

Portable .vstpreset reader/writer with no external dependencies:

#include "minihost_vstpreset.h"

char err[256];

// Read a .vstpreset
MH_VstPreset preset;
if (mh_vstpreset_read("in.vstpreset", &preset, err, sizeof(err))) {
    // Apply the processor chunk to a plugin
    mh_set_state(plugin, preset.component_state, preset.component_size);
    mh_vstpreset_free(&preset);
}

// Auto-detect the processor FUID from the plugin bundle's moduleinfo.json
// (requires VST3 SDK 3.7.5+, which all modern plugins ship).
char class_id[MH_VSTPRESET_CLASS_ID_LEN + 1];
if (!mh_vstpreset_read_class_id_from_bundle(
        "/path/to/synth.vst3", class_id, err, sizeof(err))) {
    fprintf(stderr, "Cannot determine class_id: %s\n", err);
    // For legacy plugins without moduleinfo.json, supply class_id another way
    // (e.g., copy it from an existing .vstpreset).
}

// Write current plugin state to a .vstpreset
int state_size = mh_get_state_size(plugin);
void* state = malloc(state_size);
mh_get_state(plugin, state, state_size);

mh_vstpreset_write("out.vstpreset",
                   class_id,
                   state, state_size,
                   NULL, 0,  // optional controller state
                   err, sizeof(err));
free(state);

Thread Safety

minihost runs a dedicated native plugin thread and marshals every thread-affine plugin operation onto it -- construction, destruction, and control-plane queries (state, parameter text, program names, reset, set_sample_rate, processing precision). This makes plugins safe to build on one thread and use or close from another (which is what makes open_async work), and hardens the whole library against cross-thread use.

• process* functions (process, process_midi, process_auto, process_double, process_sidechain): the real-time path -- lock-free, call from a single thread (typically the audio thread). Not marshaled.

• All other (control) functions: safe to call from any thread.

• Reconfiguring calls (set_sample_rate, set_state, set_processing_precision, set_non_realtime, reset) must not overlap a process* call -- they reconfigure the audio pipeline while process runs unprotected. Stop processing before calling them.

• Set the environment variable MINIHOST_MESSAGE_THREAD=0 to disable the plugin thread (operations then run inline on the caller's thread; cross- thread plugin use, including open_async, becomes unsafe).

API Reference

Detailed API documentation:

• C API Reference -- minihost.h, minihost_audio.h, minihost_audiofile.h, minihost_chain.h, minihost_midi.h, minihost_vstpreset.h

• Python API Reference -- Plugin, PluginChain, AudioDevice, MidiFile, MidiIn, audio I/O, MIDI rendering, automation, VST3 presets

• Hosting Guide -- practical guide with extended examples

License

GPL3