Podcast Studio Audio Router (Selective-Mesh WebRTC)

A lightweight, no-install mobile web application designed to handle the specific mix-minus audio routing needs of a podcast studio with three local hosts and one remote guest.

📡 Routing Architecture

To prevent audio feedback loops and latency in the studio, the application uses a Selective-Mesh WebRTC topology. Rather than a full mesh where everyone connects to everyone:

• Remote Guest establishes a bi-directional connection to Host 1, 2, and 3.
• Hosts 1-3 only connect to the Guest. They do not connect to each other.
• This ensures that local studio hosts (who can hear each other naturally in the room) only receive the remote guest's audio, and the guest receives a mix of all three hosts.

---

🛠️ Development Mode Instructions

1. Prerequisites & Installation

Ensure you have Node.js installed, clone the repository, and install dependencies:

npm install

2. Running the Server Locally

To start the signaling and static file server:

npm start

By default, the server runs on port 3003 (or checks the PORT environment variable).

• Local access: http://localhost:3003

3. Simulating/Testing Locally

Open multiple browser tabs or devices on your network:

• Open tab 1: Select Host 1
• Open tab 2: Select Remote Guest
• The connection indicators will turn green (Session Active), and audio level meters will begin rendering dynamically.

4. Shutting Down the Server

• Interactive Mode: Focus on the terminal window and press Ctrl + C.
• Background Mode (Kill by Port): If the server was run in the background or terminal was closed:

  fuser -k 3003/tcp

• Kill all Node processes:

  pkill node

5. Running with Docker (Alternative)

You can run the application using Docker without installing Node.js locally:

Prerequisites: Docker and Docker Compose installed.

# Build and start the container
docker compose up -d

# View logs
docker compose logs -f

# Stop the container
docker compose down

The server will be available at http://localhost:3003.

---

🌐 Overcoming Network Restrictions (Wi-Fi Isolation & Firewalls)

When testing on public, university, or corporate Wi-Fi networks, you may encounter connectivity issues:

1. AP/Client Isolation: Router prevents devices on the same Wi-Fi from talking to each other (local hosts can't reach the PC's IP).
2. Firewall Web Filtering (e.g., Fortinet): Firewall blocks tunnels like Ngrok with security warnings (net::ERR_CERT_AUTHORITY_INVALID).

Easiest Workaround: Mobile Hotspot

1. Turn on a Wi-Fi Hotspot on a mobile phone (using cellular data).
2. Connect your Studio PC and the hosts' phones to this hotspot.
3. This creates a direct local network with no blocks or AP isolation.

SSH Tunneling (Alternative to Ngrok)

If you cannot use a hotspot and Fortinet is blocking Ngrok, run a tunnel over standard SSH using the free localhost.run service:

ssh -o StrictHostKeyChecking=no -R 80:localhost:3003 nokey@localhost.run

Have local hosts and guests turn off Wi-Fi on their phones and connect to the generated public HTTPS link using their 4G/5G cellular data to bypass local network blocks.

---

🚀 Production Mode Instructions

To deploy this in your university cloud or public hosting behind an Apache reverse proxy:

1. SSL/HTTPS Requirement (Mandatory)

Browsers strictly block microphone access (navigator.mediaDevices.getUserMedia) on insecure origins. The production server must be served over HTTPS with a valid SSL certificate.

2. Apache Reverse Proxy Configuration

You must proxy both standard HTTP traffic and upgrade WebSocket connection requests (ws:// / wss://). Enable the required modules:

sudo a2enmod proxy proxy_http proxy_wstunnel rewrite ssl headers

Add the following configuration to your VirtualHost file:

<VirtualHost *:80>
    ServerName audio.youruniversity.edu
    Redirect permanent / https://audio.youruniversity.edu/
</VirtualHost>

<VirtualHost *:443>
    ServerName audio.youruniversity.edu

    SSLEngine on
    SSLCertificateFile /etc/letsencrypt/live/audio.youruniversity.edu/fullchain.pem
    SSLCertificateKeyFile /etc/letsencrypt/live/audio.youruniversity.edu/privkey.pem

    ProxyRequests Off
    ProxyPreserveHost On

    # Proxy WebSocket Traffic first (Signaling)
    RewriteEngine On
    RewriteCond %{HTTP:Upgrade} =websocket [NC]
    RewriteRule ^/(.*)           ws://localhost:3003/$1 [P,L]

    # Proxy HTTP Traffic (Frontend Files)
    ProxyPass / http://localhost:3003/
    ProxyPassReverse / http://localhost:3003/

    # Security Headers for Device Access Permissions
    Header always set Referrer-Policy "no-referrer-when-downgrade"
    Header always set Feature-Policy "microphone 'self'"
</VirtualHost>

3. Handling Strict Firewalls (TURN Server Fallback)

If university clients fail to establish audio routes (connections stay on Connecting... or Failed), firewalls are likely blocking direct UDP streams. To resolve this:

1. Set up a Coturn server on your cloud node.
2. Update the WebRTC configuration array in public/app.js to include your TURN credential credentials:

   const rtcConfig = {
     iceServers: [
       { urls: 'stun:stun.l.google.com:19302' },
       { 
         urls: 'turn:your-turn-server.edu:3478',
         username: 'your-username',
         credential: 'your-password'
       }
     ]
   };