# headroom

Automatic loudness and per-app volume control for PipeWire, in Rust.

Headroom puts a per-application audio safety net between noisy sources
(browsers, voice chat, random video) and your speakers, while leaving
the things you *don't* want compressed (music players, games, DAWs)
untouched.

- **Hard −0.1 dBTP ceiling on the processed route**, with proper
  inter-sample-peak handling, enforced inline so the contract holds
  regardless of control-plane state. Streams routed `bypass` ride the
  real sink directly and are not in scope of the contract — that's the
  trade-off that makes the per-app exclusion useful.
- **Per-app exclusion** with profile-driven rules.
- **Layer A per-app level control** (peak + RMS detector → smoothed
  `channelVolumes` writes) for taming individual streams without
  touching the bus path. Zero added signal-path latency; safe to use
  on bypass-routed streams.
- **Single binary** daemon + CLI, controlled over a Unix-domain socket
  with a documented JSON wire protocol (see [`IPC.md`](IPC.md)).
- **First-party Rust crate** (`headroom-client`) for programmatic use;
  third-party clients (Qt panels, status bars, …) target the wire
  protocol directly.
- **Live profile reload** — edit a TOML file in
  `$XDG_CONFIG_HOME/headroom/profiles/` and the daemon picks up
  changes within ~500 ms; the audio thread doesn't glitch.

See [`PLAN.md`](PLAN.md) for the full design and roadmap.

## Status

Alpha. The signal chain (AGC, compressor, two-tier limiter, Layer A
per-app), the routing engine (explicit-link enforcement, sink hotplug,
sticky default sink), the IPC server with topic subscriptions, the
`headroom monitor` TUI, and live profile reload all work end-to-end.
Packaging exposes a systemd user unit and Nix modules. What's missing
is real-world soak time on multi-rate / Bluetooth setups and other
distros' init systems.

## Installing

### Nix (flake)

This repo is a flake; the daemon plus its systemd user unit and the
canonical profiles are exposed as a package.

```sh
nix run github:atagen/headroom -- daemon          # one-shot run
nix profile install github:atagen/headroom        # add to $PATH
```

For **Home Manager**, add the flake as an input and enable the module:

```nix
{
  inputs.headroom.url = "github:atagen/headroom";

  # In your Home Manager configuration:
  imports = [ inputs.headroom.homeModules.default ];
  services.headroom.enable = true;
}
```

The module symlinks the shipped profiles into
`$XDG_CONFIG_HOME/headroom/profiles/`, drops the systemd user unit
into the user's services dir, and the unit starts after PipeWire and
WirePlumber come up. `services.headroom.extraProfiles` lets you add
your own.

For **NixOS** (system-wide binary install + systemd-user discovery):

```nix
{
  inputs.headroom.url = "github:atagen/headroom";

  # In your NixOS configuration:
  imports = [ inputs.headroom.nixosModules.default ];
  programs.headroom.enable = true;
}
```

Then any user can `systemctl --user enable --now headroom`.

### Other distros (manual)

```sh
cargo install --path crates/headroom-cli   # or: cargo build --release
# Profiles
mkdir -p ~/.config/headroom/profiles
cp profiles/*.toml ~/.config/headroom/profiles/
# systemd user unit (edit the ExecStart path to point at your binary)
install -Dm644 contrib/systemd/headroom.service \
  ~/.config/systemd/user/headroom.service
sed -i "s|@bindir@|$(dirname "$(command -v headroom)")|" \
  ~/.config/systemd/user/headroom.service
systemctl --user daemon-reload
systemctl --user enable --now headroom
```

## Usage

Once the daemon is running:

```sh
headroom status                 # JSON snapshot — sinks, streams, active profile
headroom profile list           # available profiles
headroom profile use night      # activate one
headroom monitor                # full-screen TUI (bus gauges + per-stream)
headroom monitor --json meters  # line-delimited JSON, for scripting
headroom route set firefox processed
headroom set compressor.threshold_db -28
headroom bypass on              # kill switch — straight to the real sink
```

See `headroom --help` for the full surface.

## Building

```sh
nix develop          # toolchain + pipewire dev libs + helpers
cargo build          # iterate
cargo test --workspace
nix build            # final packaged headroom binary
```

## License

GPL-3.0-or-later for the daemon and CLI. `headroom-dsp` and `headroom-ipc`
are MPL-2.0 so they can be reused by non-GPL plugin hosts and clients.