Audio Bridge (Rust, v1)

A cross-platform, low-latency LAN audio bridge between Linux and macOS.
It captures “what you hear” (system or app audio), encodes with Opus, ships over RTP/UDP, and plays it on the other machine.

Think “DIY Dante Lite” for home/office, written in Rust.

---

✨ Features

• 🔄 Bidirectional streaming (run on both machines).
• 🎧 Captures system audio (BlackHole on macOS, PipeWire monitor on Linux).
• ⚡ Low-latency Opus (2.5–5 ms frames).
• 🔊 Automatic playback on system speakers.
• 🌐 Optional mDNS advertisement for peer auto-discovery.

---

🔧 Setup

macOS

cd scripts
./macos_setup.sh

This installs:

• GStreamer + plugins
• BlackHole 2ch (virtual device)
• SwitchAudioSource CLI

Then in Audio MIDI Setup:

• Create a Multi-Output Device with:

  • ✅ BlackHole 2ch
  • ✅ Your speakers (MacBook Speakers / Headphones)

• Set it as the default output.

---

Linux (PipeWire)

cd scripts
./linux_setup.sh

This installs:

• GStreamer + plugins
• PipeWire + WirePlumber
• Pulseaudio utils (pactl)

It also creates a null sink called bridge_out. Use its .monitor source as your TX input.

---

🛠️ Build the Daemon

Install Rust (1.75+ recommended):

cargo build --release

Binary is at:

target/release/ab-daemon

---

🚀 Run It

Linux (receiver only):

./target/release/ab-daemon --listen-port 5004

macOS (sender + receiver):

AB_SRC_BUFFER_US=200000 AB_SRC_LATENCY_US=10000 \
./target/release/ab-daemon \
  --capture-device "BlackHole 2ch" \
  --send-to <LINUX_IP> \
  --send-port 5002 \
  --listen-port 5004

• Replace <LINUX_IP> with your Linux machine’s LAN IP.
• Run the reverse command on Linux (with --send-to <MAC_IP>) for full duplex.

💡 Note: AB_SRC_BUFFER_US and AB_SRC_LATENCY_US are critical on macOS. Start with 200000 / 10000 and tune as needed.

---

🔍 Quick Test (without daemon)

macOS → Linux

# macOS (sender)
gst-launch-1.0 osxaudiosrc device="BlackHole 2ch" \
  ! audioconvert ! audioresample \
  ! opusenc frame-size=2.5 bitrate=256000 \
  ! rtpopuspay pt=97 \
  ! udpsink host=<LINUX_IP> port=5004

# Linux (receiver)
gst-launch-1.0 udpsrc port=5004 caps="application/x-rtp,media=audio,encoding-name=OPUS,clock-rate=48000,pt=97" \
  ! rtpjitterbuffer latency=30 drop-on-late=true do-lost=true \
  ! rtpopusdepay ! opusdec \
  ! audioconvert ! audioresample ! pipewiresink

---

🐞 Troubleshooting

• Silence on macOS sender Ensure you run from the Terminal (not VSCode), so the app has microphone permissions. Set AB_SRC_BUFFER_US=200000 and AB_SRC_LATENCY_US=10000.

• CoreAudio device not found Check your device list with:

  gst-device-monitor-1.0 Audio

  Then use the correct --capture-device <INDEX>.

• Linux internal mic sounds noisy Use the .monitor source of a null sink (e.g., bridge_out.monitor) instead of the raw mic.

• No audio on Linux playback Confirm the RTP caps match exactly (payload=97, clock-rate=48000, encoding-name=OPUS).

---

🛣️ TODO

• Drift correction (adaptive resampling).
• SRTP/DTLS encryption.
• WebRTC transport for WAN.
• GUI (Tauri tray app with meters).
• Per-app routing (Loopback on macOS, PipeWire filters on Linux).
• Better install scripts (brew/apt).
• Smart Setup Scripts, that handles inputs and outputs cleanly, and save the default for graceful exit.
• Graceful exit, currently it's just Ctrl + C, re assigns the inputs and outputs to what they were.
• Add smarter handling for the same in case is they want to pause the connection or similar.
• Make it adaptable to windows too.

---

📜 License

MIT