Initial extraction: C++ MixerEngine standalone daemon

Extracted from op-pedal mixer-engine branch. Core components: - MixerEngine / MixerChannelStrip / MixerBus — cleaned of LV2/Pedalboard/IHost/MidiMapper deps - MixerControlServer — Unix domain socket JSON control interface - main.cpp — JACK audio I/O client with headless fallback - CMake build — auto-fetches nlohmann/json, links JACK - 9 core tests passing Architecture: JACK ports → MixerEngine::process() → JACK ports, controlled via Unix socket JSON commands.
2026-06-23 12:17:45 -04:00
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+# OPLabs Mixer Engine — Standalone Daemon
+
+C++ standalone audio mixer daemon, extracted from the op-pedal mixer-engine branch. JACK audio I/O with Unix socket JSON control.
+
+## Architecture
+
+```
+JACK Ports → MixerEngine::process() → JACK Ports
+                  ↕
+         MixerControlServer (Unix socket)
+                  ↕
+         FastAPI bridge (future) / socat / nc
+                  ↕
+         React Mixer Console (browser)
+```
+
+### Processing Pipeline (per audio cycle)
+
+1. Clear all bus buffers
+2. For each channel: apply HPF → volume/pan → accumulate to routed buses
+3. Process aux sends (pre/post fader)
+4. Route buses to buses according to routing matrix
+5. Process each bus (apply volume, compute VU)
+6. Write to physical outputs per output routing table
+
+## Dependencies
+
+- **JACK** (libjack-jackd2-dev on Debian, jack-audio-connection-kit-devel on Fedora)
+- **CMake** >= 3.16
+- **C++17** compiler
+- **nlohmann/json** (auto-fetched by CMake)
+
+## Build
+
+```bash
+git clone <repo-url> oplabs-mixer-daemon
+cd oplabs-mixer-daemon
+mkdir build && cd build
+cmake ..
+make -j$(nproc)
+```
+
+## Run
+
+```bash
+# Start JACK first
+jackd -d alsa -r 48000 -p 256 -n 3 &
+
+# Run the daemon (auto-connects to JACK)
+./mixer-daemon
+
+# With custom config
+./mixer-daemon --inputs 4 --outputs 2 --buffer-size 128
+```
+
+### Command-line Options
+
+| Option | Default | Description |
+|--------|---------|-------------|
+| `--socket <path>` | `/tmp/mixer-daemon.sock` | Unix socket path |
+| `--inputs <N>` | 2 | Number of JACK input channels |
+| `--outputs <N>` | 2 | Number of JACK output channels |
+| `--sample-rate <N>` | 48000 | Audio sample rate (overridden by JACK) |
+| `--buffer-size <N>` | 256 | Audio buffer size in frames (overridden by JACK) |
+| `--help` | | Show help |
+
+### Headless Mode
+
+If JACK is not running, the daemon starts in headless mode — no audio I/O, but the control socket is active for testing.
+
+## Control Protocol
+
+The daemon listens on a Unix domain socket. Send one JSON command per line, receive one JSON response per line.
+
+```bash
+# Get full mixer state
+echo '{"cmd":"getState"}' | nc -U /tmp/mixer-daemon.sock
+
+# Set channel volume
+echo '{"cmd":"setChannelVolume","channel":0,"volume":-6.0}' | nc -U /tmp/mixer-daemon.sock
+
+# Get VU levels
+echo '{"cmd":"getVU"}' | nc -U /tmp/mixer-daemon.sock
+
+# Auto-create channels
+echo '{"cmd":"autoCreateChannels","inputs":4,"outputs":2}' | nc -U /tmp/mixer-daemon.sock
+```
+
+### Commands
+
+| Command | Parameters | Description |
+|---------|------------|-------------|
+| `getState` | — | Full mixer state as JSON |
+| `getVU` | — | VU levels per channel and bus |
+| `setChannelVolume` | `channel`, `volume` | Set channel fader (-96..+12 dB) |
+| `setChannelPan` | `channel`, `pan` | Set pan (-1.0 left to 1.0 right) |
+| `setChannelMute` | `channel`, `mute` | Mute toggle |
+| `setChannelSolo` | `channel`, `solo` | Solo toggle |
+| `setChannelLabel` | `channel`, `label` | Set channel name |
+| `setBusVolume` | `busId`, `volume` | Set bus fader (-96..+12 dB) |
+| `setBusMute` | `busId`, `mute` | Bus mute toggle |
+| `routeChannelToBus` | `channel`, `busId`, `level` | Route channel to bus |
+| `routeBusToBus` | `sourceBusId`, `targetBusId`, `level` | Route bus to bus |
+| `removeRoute` | `sourceId`, `targetBusId` | Remove a route |
+| `autoCreateChannels` | `inputs`, `outputs` | Recreate all channels for N inputs |
+| `addChannel` | `physicalInput` | Add a new channel strip |
+| `removeChannel` | `channel` | Remove a channel strip |
+
+## Run Tests
+
+```bash
+cd build && ctest
+# or
+./mixer-test
+```
+
+## Integration
+
+The daemon is designed to sit behind a FastAPI Python bridge that translates HTTP/WebSocket to Unix socket commands. That bridge then serves the React Mixer Console UI.
+
+## License
+
+Copyright (c) 2026 Ourpad Network. See LICENSE file.