AirLink

Low-latency, high-fidelity two-way P2P audio link. Both ends run the same binary.

Codec choice

Mode	What it is	Codec delay	Bandwidth (stereo)	Use it for
--codec opus (default)	Opus, CELT-only restricted low-delay mode, CBR	2.5 ms lookahead	256 kb/s (up to 510)	Internet links, perceptually transparent at 256k+
--codec pcm	Linear 24-bit / 48 kHz (L24)	0 ms	2.3 Mb/s	LAN or fat, clean links, bit-perfect audio

The default is 5 ms frames, a 20 ms jitter buffer and 1× redundancy, which gives about 27.5 ms one-way plus network and soundcard buffers. On a LAN, --frame 2.5 --jitter 5 gets you under 10 ms.

Install

Download from the GitHub Releases page:

Platform	File	Notes
Windows 10/11 x64	AirLink-<ver>-windows-x64-setup.exe	Setup wizard with Start Menu shortcut and uninstaller. Optionally adds a firewall rule so you can answer calls.
macOS 11+ (Apple Silicon + Intel)	AirLink-<ver>-macos-universal.dmg	Drag AirLink to Applications. Asks for microphone access on first call.
Debian/Ubuntu/Pi OS (amd64, arm64)	airlink_<ver>-1_<arch>.deb	sudo apt install ./airlink_*.deb. Adds a menu entry. airlink --headless for servers.

Unsigned builds: until the app is code-signed, macOS will say it "can't be checked". Right-click AirLink.app and choose Open once, or run xattr -dr com.apple.quarantine /Applications/AirLink.app. On Windows, SmartScreen will ask you to confirm: click More info → Run anyway.

Building installers

Push a tag to have GitHub Actions build every installer and publish a Release:

git tag v0.3.0 && git push origin v0.3.0

Or build locally:

# macOS -> dist/AirLink-<ver>-macos-universal.dmg
brew install cmake
./packaging/macos/build.sh
# Apple Silicon only (faster):  ARCHS=aarch64 ./packaging/macos/build.sh
# Signed + notarised: set MACOS_SIGN_IDENTITY, APPLE_ID, APPLE_TEAM_ID, APPLE_APP_PASSWORD

# Windows -> dist\AirLink-<ver>-windows-x64-setup.exe
winget install Kitware.CMake JRSoftware.InnoSetup
.\packaging\windows\build.ps1

# Linux -> target/debian/airlink_<ver>-1_<arch>.deb
sudo apt install libasound2-dev libopus-dev pkg-config cmake \
  libxkbcommon-dev libgl1-mesa-dev libwayland-dev libx11-dev
cargo install cargo-deb
cargo deb

The macOS and Windows builds compile libopus from source and link it statically, so they have no external dependencies. The .deb depends on the system libopus0 and libasound2.

Build from source

cargo build --release && ./target/release/airlink

(Install the same dependencies as above first.)

GUI

• Call / Answer: Call needs the peer address. Answer waits for whoever calls (forward UDP 5004).
• Codec, bitrate, frame size, channels, jitter buffer, redundancy, input/output device
• Live send/receive peak meters with an −18 dBFS alignment mark
• Status: Idle / Waiting / Calling / Connected (amber when lossy)
• Stats: latency estimate, buffer depth, packets/s, concealed, late, underruns, drift fixes

Headless

airlink --list
airlink --headless -i "Scarlett" -o "Scarlett"          # studio end, answers
airlink --peer studio.example.com -i "MacBook"           # remote end, calls

Useful presets

# LAN, bit-perfect, lowest latency
airlink --peer 192.168.1.50 --codec pcm --frame 2.5 --jitter 5

# Internet, transparent stereo
airlink --peer studio.example.com --bitrate 256 --frame 5 --jitter 20 --redundancy 1

# Lossy 4G, tougher
airlink --peer studio.example.com --bitrate 192 --frame 10 --jitter 60 --redundancy 2

How it works

• Capture: the soundcard callback slices audio into frames (2.5/5/10/20 ms) and hands them to the encoder thread without blocking.
• Transport: one UDP packet per frame, with a 16-byte header and a 64-bit sequence number. With --redundancy N, each packet also carries the previous N frames, so a single lost packet is recovered with no extra delay. (In CELT-only mode, Opus has no in-band FEC, so this does that job instead.)
• Jitter buffer: reorders packets by sequence number and pre-buffers to the target depth. Gaps are concealed with Opus PLC. Clock drift between the two soundcards is corrected by dropping or inserting one frame when the buffer stays outside its band for a while.
• Stats line: shows packets/s, concealed frames, late packets, buffer depth, underruns and drift corrections.

Roadmap

• Adaptive jitter target, which learns from measured network jitter
• Resampling-based drift correction instead of frame drop/insert
• Encryption (Noise/ChaCha20) and a peer password
• Directory/rendezvous server and NAT hole-punching
• Multi-network bonding
• EBU 3326 SIP mode for Comrex/Tieline interop
• Code signing (Apple Developer ID, Windows Authenticode)
• Saved settings and remote phonebook in the GUI
• Web UI for headless boxes (shared with AirSwitch)