BeamCast

Open-source AirPlay 1 (RAOP) transmitter for Windows 11 — a TuneBlade successor.

What it does

Streams Windows system audio (WASAPI loopback) to existing AirPlay 1 receivers: WiiM Mini (primary test device), Apple TV, HomePod, AirPort Express, and other RAOP speakers.

Product pillars

1. A/V sync — delay the picture in the browser to match wireless speaker latency; PC audio stays live.
2. Optional PC mute — off by default (muting the master volume also mutes WASAPI loopback).
3. Lossless ALAC — 16-bit / 44.1 kHz baseline.
4. No Apple Bonjour — own mDNS/DNS-SD sockets.

Requirements

• Windows 11 (WinUI 3 app). Core + tests also run on Linux CI.
• An AirPlay 1 / RAOP speaker on the LAN (WiiM Mini confirmed).
• .NET 10 SDK to build from source.
• Chrome or Edge for the optional beamcast-sync extension.

Stack

• .NET 10 LTS, C# / WinUI 3 (Windows App SDK, unpackaged, self-contained)
• WASAPI loopback (CsWin32) → format convert → ALAC (Apple encoder port, Apache-2.0) → RAOP/RTP
• Bouncy Castle — RSA/AES/Digest when the receiver requires encryption (et=1)
• Tests: xUnit + headless MockRaopReceiver

src/
  AirNext.Core/        # RAOP, mDNS, audio pipeline (no UI)
  AirNext.Core.Tests/  # xUnit
  AirNext.Audio/       # WASAPI capture/render (Windows)
  AirNext.App/         # WinUI 3 tray + window
  AirNext.StreamProbe/ # CLI live-stream probe
  AirNext.CaptureProbe/# WASAPI / latency-test probe
extensions/beamcast-sync/  # Chrome MV3 video delay

Build

# Core + tests (Linux / macOS / Windows)
dotnet test src/AirNext.Core.Tests/AirNext.Core.Tests.csproj -c Release

# App — Windows 11 only (XamlCompiler). On Win11:
dotnet build src/AirNext.App/AirNext.App.csproj -c Debug

Run the app from the output exe (do not rely on dotnet run for WinUI):

src\AirNext.App\bin\Debug\net10.0-windows10.0.26100.0\win-x64\AirNext.App.exe

Installer (Windows 11)

No admin. Installs to %LOCALAPPDATA%\Programs\BeamCast.

winget install JRSoftware.InnoSetup
powershell -ExecutionPolicy Bypass -File installer\build.ps1

Then run artifacts\BeamCast-Setup.exe. Start Menu shortcut BeamCast. Uninstall from Settings → Apps.

Log: %LOCALAPPDATA%\BeamCast\beancast.log
Settings: %LOCALAPPDATA%\BeamCast\settings.json

Close TuneBlade while testing (it holds UDP 6002/6003).

Chrome extension (lip-sync)

Unpacked load: extensions/beamcast-sync/ (chrome://extensions → Developer mode → Load unpacked).

The app serves http://127.0.0.1:46382/metrics (delayMs, streaming state). The extension delays video frames (canvas ring) and never pauses <video> audio — WASAPI needs it.

• YouTube: status chip in .ytp-right-controls (left of settings / fullscreen).
• Other sites: HUD, bottom-right.

Reload the extension after each pull.

Usage

• Click a compatible device (port 7000) or Start — streams system audio.
• Stop — TEARDOWN. Pause — FLUSH without a full reconnect.
• Auto-stream last-used device on launch (Advanced, on by default). WiiM/Linkplay often takes ~45–60 s to answer mDNS.
• RealTime must be on before Start. Delay slider 20–250 ms (default 40). Normal mode uses a ~3 s sync anchor.
• Mute PC while streaming is off by default — master-volume mute also silences WASAPI loopback.
• Closing the window hides to the tray (stream keeps running). Right-click the tray icon → Exit to quit.
• Close TuneBlade while testing (it holds UDP 6002/6003).

License

MIT. The ALAC encoder is a port of Apple’s reference encoder (Apache-2.0).