midimi

A magical music box for MIDI — play, explore, and watch your music.

midimi is a native desktop MIDI player and visualizer built with Tauri v2 (Rust backend) and SvelteKit + Svelte 5 (frontend). Drop in a .mid file and watch it come alive: a full-screen "Cosmic Aurora" visualization reacts to every note in real time, while a bundled General MIDI soundfont renders the audio entirely in Rust — no browser audio engine, no drift. Transport controls let you play, pause, seek, adjust tempo and volume. Recent files and settings persist across launches. Licensed Apache-2.0.

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Prerequisites

• Rust (stable toolchain)
• Node.js 20+
• macOS, Linux (with WebKit2GTK + libasound), or Windows

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Setup

# 1. Fetch the bundled soundfont (~31 MB, one-time download)
./scripts/fetch-soundfont.sh

# 2. Install JS dependencies
npm install

# 3. Launch in dev mode (hot-reload frontend, Rust recompiles on change)
npm run tauri dev

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Build

npm run tauri build

Produces a platform-native installer in src-tauri/target/release/bundle/.

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Project layout

src/                  SvelteKit frontend (SPA, SSR off)
  routes/+page.svelte   Root page — state, playhead listener, file open
  lib/
    ipc.ts              Typed wrappers for every Tauri invoke + event
    types.ts            Shared TS interfaces (Note, MidiData, Playhead, …)
    theme.ts            Three built-in themes (Cosmic, Nebula Rose, Abyss)
    VizCanvas.svelte    Canvas host + note scheduler
    visualizations/
      types.ts          Visualization plugin interface
      cosmic-aurora.ts  Bundled aurora visualization (Canvas 2D)
    Transport.svelte    Play/pause/seek/tempo/volume controls
    TrackList.svelte    Track name list
    SoundfontPicker.svelte  SF2 loader + switcher
    ThemePicker.svelte  Theme selector
src-tauri/src/        Rust backend
  lib.rs              App setup, resource resolution, 60 Hz playhead loop
  commands.rs         Tauri command handlers
  midi.rs             MIDI parser → note timeline
  audio.rs            AudioEngine, render thread, rtrb ring buffer, cpal
  analysis.rs         Hann-windowed FFT, 16 log-spaced bands, RMS
  db.rs               Turso embedded SQLite cache
assets/soundfonts/    GeneralUser GS license
scripts/              fetch-soundfont.sh
docs/
  ARCHITECTURE.md     Data flow, module map, Visualization plugin contract
  DECISIONS.md        ADR log (8 decisions)

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Docs

• Architecture — data flow, module map, Visualization plugin contract
• Design Decisions — ADR log

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License

Apache-2.0 — see LICENSE.

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Third-party assets

GeneralUser GS v2.0 by S. Christian Collins
A permissive General MIDI soundfont bundled with midimi for out-of-box audio playback.
License: assets/soundfonts/GeneralUser-GS-LICENSE.txt
Source: https://github.com/mrbumpy409/GeneralUser-GS