midlman

A MIDI-to-Windows-audio-mixer bridge written in Rust. midlman reads input from a MIDI controller (sliders, dials, and buttons) and uses it to control per-application volume and mute on Windows, via the Core Audio (WASAPI) session API.

Think of it as a hardware mixing desk for your Windows audio sessions, controlled from any class-compliant MIDI device.

How it works

1. midlman lists the active Windows audio sessions (one per running application with audio output) along with their current volume.
2. It opens a connection to your MIDI controller and waits for input.
3. A preset (YAML) describes which MIDI CC numbers on your controller correspond to sliders, dials, and buttons.
4. Component bindings map specific CC numbers to specific audio sessions, for example slider 5 to Spotify's volume, button 25 to Spotify's mute.
5. Moving a slider/dial or pressing a button sends a MIDI Control Change message, which midlman translates into a volume or mute call against the matching session.
6. SysEx messages are used to switch banks, so a single controller can address more application bindings than it has physical components.

Requirements

• Windows (the audio backend uses the Win32 Core Audio APIs directly)
• Rust toolchain (cargo)
• A class-compliant MIDI controller with sliders, dials, and/or buttons

Building

git clone https://github.com/ChemicalLuck/midlman.git
cd midlman
cargo build --release

The binary is built as midlman (see [[bin]] in Cargo.toml).

Presets

A preset declares which CC numbers belong to each component type, as comma-separated values and ranges:

components:
  sliders: "3-11"
  buttons: "1,2,23-31,44-49,64,67"
  dials: "12-22"

midlman currently loads a preset from a hardcoded path, data/subzero.yaml, at startup. You'll need to create a data/ directory in the project root and add your controller's preset there before running.

Bindings

Component-to-session bindings (which CC controls which application) are currently wired up in code rather than config, see the Spotify example in src/main.rs:

controller.bind_component(
    u7::from(5),
    Box::new(move |value| {
        let normalized = value.as_int() as f32 / 127.0;
        spotify_session.lock().unwrap().set_volume(normalized);
    }),
);

To target a different application, change the session name passed to get_session_by_name and the CC numbers passed to bind_component.

Running

cargo run --release

On startup, midlman will:

• Print all active audio sessions and their current volume
• Prompt you to select a MIDI input port if more than one is connected
• Begin listening for MIDI input until you press Enter to exit

Pass --debug to print every incoming Control Change and SysEx message as it arrives, useful for finding the CC numbers your controller sends:

cargo run --release -- --debug

Project layout

src/
├── main.rs              # Entry point, session discovery, example bindings
├── midi/
│   ├── mod.rs            # Port selection
│   ├── controller.rs     # Controller — bank-aware component lookup and dispatch
│   ├── preset.rs         # Preset / PresetComponents — YAML schema
│   └── components/       # Slider, Dial, Button component types
└── volume/
    ├── mod.rs
    ├── session.rs         # Session — per-application volume/mute wrapper
    └── winaudio.rs        # AudioController — Win32 Core Audio session enumeration

License

No license file is currently included in this repository.