An ultra-low latency, zero-compromise Remote Microphone Streaming Pipeline. This monorepo implements a real-time WebRTC audio relay engine designed to capture broadcast-grade voice from an edge mobile client, traverse restrictive international networks, and inject the stream directly into a native Virtual Audio Cable (VAC) on a home base machine.
The resulting virtual device serves as an enterprise-grade hardware microphone source for platforms like Microsoft Teams, Zoom, and Webex, completely bypassing high-overhead, generic commercial streaming utilities.
When working remotely across international boundaries—often bound to unpredictable hotel Wi-Fi, complex symmetric NATs, and high-jitter residential ISP routings—joining critical corporate meetings with stable audio is a massive hurdle. Generic streaming apps favor heavy media buffering (introducing high latency) or introduce massive CPU/network overhead.
AirMic-Sink solves this by stripping away everything except the raw essentials needed for high-velocity voice processing.
- Zero-Overhead Plumbing: Pure .NET stack using minimal execution runtimes to cut down scheduling jitter.
- Direct Hardware Injection: Bypasses the Windows System Mixer via WASAPI Exclusive Mode (
IAudioClient3) to eliminate internal OS audio latency down to the millisecond. - Resilient Network Traversal: Built specifically to survive aggressive hospitality firewalls via strategic STUN/TURN UDP fallbacks and lightweight signaling.
- Antigravity 2.0 Realization: Fully realized and optimized using Antigravity 2.0 principles to maintain absolute structural performance, lightweight data state transitions, and extreme resilience against network throughput degradation.
The pipeline is organized as a unified .NET Monorepo split into highly specialized, isolated boundaries:
📁 AirMic-Sink/
│
├── 📁 src/
│ ├── 📁 AirMic.Server/ # ASP.NET Core Minimal API WebSockets Hub (Docker/IIS-ready)
│ ├── 📁 AirMic.Receiver/ # Desktop Engine (SIPSorcery WebRTC State Machine + WASAPI Sink)
│ └── 📁 AirMic.Client/ # Mobile Capture Edge (.NET MAUI / Blazor Hybrid)
│
├── 📁 shared/
│ └── 📁 AirMic.Contracts/ # Zero-dependency POCOs for SDP and ICE Candidate routing
│
└── 📄 AirMic-Sink.sln # Master Solution
[ Mobile Mic ] ──(Low-Delay WebRTC / Opus)──> [ Cloud / Home Lab Signaling ]
│
(P2P WebRTC / UDP Stream)
│
▼
[ MS Teams / Zoom ] <─── [ Cable Output ] <─── [ WASAPI Exclusive Sink ]
To preserve deterministic real-time communication across networks, the engine enforces specialized, lightweight constraints across all layers:
- Voice-Speech Optimized Mode (Recommended): Tailored for meetings and calls. Captures at 48,000 Hz Mono at a clamped bitrate of 24 kbps. It enables browser echo cancellation, noise suppression, and automatic gain control to deliver highly intelligible speech while using extremely low network bandwidth.
- Music / High-Fidelity Mode: Tailored for rich, unfiltered sound. Captures raw 48,000 Hz Stereo at a bitrate of 64 kbps. It disables all client-side browser DSP audio filters to ensure raw, unmodified audio delivery.
To prevent chattering and dropout oscillation under network jitter, the receiver-side WASAPI exclusive playback queue implements a dynamic watermark threshold:
- Voice Mode: Limits backlog to a 200ms trigger, truncating down to a 120ms low-watermark cushion.
- Music Mode: Prioritizes absolute stability, using a 300ms trigger and a 135ms cushion.
- Codec Selection: Locked to the high-performance Opus codec.
- Packetization Rate (ptime): Configured at 20ms frame sizes for optimal packet header overhead vs network latency.
- Sample Rate Lock: Enforced at a unified 48,000 Hz across the pipeline to eliminate CPU-intensive resampling filters at the client-side capture and receiver-side playback.
- Clean Console Output: The receiver's console output is kept clear of clutter—displaying only connection transitions and active error alerts. Intermediate SDP negotiations, ICE updates, and WASAPI buffer thresholds are redirected to structured logs in the
logs/directory. - Restricted Loopback Testing: Loopback recording and streaming back are restricted exclusively to
_isTestModesessions. During normal stream usage, loopback capture is fully deactivated to protect resources and prevent audio bleed.
- Signaling Channel: Stateless C# Minimal API WebSockets router handling pure SDP Offer/Answer exchanges and immediate ICE candidate forwarding.
- Security Context: Implements a lean, high-velocity pre-shared "Stream Secret Key" parameter validation on the WebSockets upgrade pathway to instantly drop unauthenticated probes.
- Transport Layer: Prioritizes raw peer-to-peer UDP streams to eliminate TCP Head-of-Line blocking over jitter-prone hospitality Wi-Fi.
- WASAPI Exclusive Mode: Targets the Virtual Audio Cable input buffer using
AudioClientShareMode.Exclusive. This grantsAirMic.Receiverdirect, uninterrupted access to the hardware device driver data ring, dodging the latency penalty of the Windows audio rendering subsystem. - Cross-Platform Forward Compatibility: Architected via interface abstraction (
IAudioBufferSink). The receiver easily adapts to macOS in the future by hot-swapping the Windows WASAPI layer for a Mac CoreAudio / BlackHole Virtual Loopback engine without touching the network or signaling infrastructure.
- VB-Audio Virtual Cable or Virtual Audio Cable (VAC) installed on the target Windows Receiver machine.
- A functional Cloudflare Tunnel (or similar reverse proxy) exposing the signaling hub securely over
HTTPS/WSSto satisfy mobile browser and native application microphone permission restrictions.
Before launching network code, verify your local audio routing matrix. Run the local test fixture in AirMic.Receiver to generate an isolated, continuous 440Hz wave directly into your Virtual Audio Cable:
dotnet run --project src/AirMic.Receiver --mode test-sink
- Validation: Open your meeting software (Teams/Zoom), switch the microphone input source to Cable Output, and execute an audio loopback check. If you observe a crisp, uncorrupted synthetic tone free of crackle or distortion, the WASAPI injection loop is validated.
Deploy the signaling hub directly to Docker inside your homelab environment:
docker build -t airmic-server -f src/AirMic.Server/Dockerfile .
docker run -d -p 8443:8443 -e PORT=8443 -e STREAM_SECRET="YourSecretKeyHere" airmic-server
Hook up your Cloudflare Tunnel to map an external secure endpoint straight to internal port 8443.