Realtime Twilio Integration

This example demonstrates how to connect the OpenAI Realtime API to a phone call using Twilio's Media Streams. The server handles incoming phone calls and streams audio between Twilio and the OpenAI Realtime API, enabling real-time voice conversations with an AI agent over the phone.

Prerequisites

• Python 3.10+
• OpenAI API key with Realtime API access
• Twilio account with a phone number
• A tunneling service like ngrok to expose your local server

Setup

1. Start the server:

   bashCopy

   uv run server.py
   

   The server will start on port 8000 by default.

2. Expose the server publicly, e.g. via ngrok:

   bashCopy

   ngrok http 8000
   

   Note the public URL (e.g., https://abc123.ngrok.io)

3. Configure your Twilio phone number:

   • Log into your Twilio Console
   • Select your phone number
   • Set the webhook URL for incoming calls to: https://your-ngrok-url.ngrok.io/incoming-call
   • Set the HTTP method to POST

Usage

1. Call your Twilio phone number
2. You'll hear: "Hello! You're now connected to an AI assistant. You can start talking!"
3. Start speaking - the AI will respond in real-time
4. The assistant has access to tools like weather information and current time

How It Works

1. Incoming Call: When someone calls your Twilio number, Twilio makes a request to /incoming-call
2. TwiML Response: The server returns TwiML that:
   • Plays a greeting message
   • Connects the call to a WebSocket stream at /media-stream
3. WebSocket Connection: Twilio establishes a WebSocket connection for bidirectional audio streaming
4. Transport Layer: The TwilioRealtimeTransportLayer class owns the WebSocket message handling:
   • Takes ownership of the Twilio WebSocket after initial handshake
   • Runs its own message loop to process all Twilio messages
   • Handles protocol differences between Twilio and OpenAI
   • Automatically sets G.711 μ-law audio format for Twilio compatibility
   • Manages audio chunk tracking for interruption support
   • Wraps the OpenAI realtime model instead of subclassing it
5. Audio Processing:
   • Audio from the caller is base64 decoded and sent to OpenAI Realtime API
   • Audio responses from OpenAI are base64 encoded and sent back to Twilio
   • Twilio plays the audio to the caller

Configuration

• Port: Set PORT environment variable (default: 8000)
• OpenAI API Key: Set OPENAI_API_KEY environment variable
• Agent Instructions: Modify the RealtimeAgent configuration in server.py
• Tools: Add or modify function tools in server.py

Troubleshooting

• WebSocket connection issues: Ensure your ngrok URL is correct and publicly accessible
• Audio quality: Twilio streams audio in mulaw format at 8kHz, which may affect quality
• Latency: Network latency between Twilio, your server, and OpenAI affects response time
• Logs: Check the console output for detailed connection and error logs

Architecture

Phone Call → Twilio → WebSocket → TwilioRealtimeTransportLayer → OpenAI Realtime API
                                              ↓
                                      RealtimeAgent with Tools
                                              ↓
                           Audio Response → Twilio → Phone Call

The TwilioRealtimeTransportLayer acts as a bridge between Twilio's Media Streams and OpenAI's Realtime API, handling the protocol differences and audio format conversions. It wraps the OpenAI realtime model to provide a clean interface for Twilio integration.