This example demonstrates bidirectional audio streaming with the OpenAI Realtime API using PromptKit.

Features

• Bidirectional Audio Streaming: Send and receive audio simultaneously at 24kHz
• Server-Side VAD: OpenAI’s voice activity detection handles turn-taking
• Function Calling: Execute tools/functions during streaming sessions
• Input Transcription: Get transcripts of what the user said
• Multiple Voices: Choose from alloy, echo, shimmer, ash, ballad, coral, sage, verse

Prerequisites

1. OpenAI API Key with Realtime API access
2. PortAudio (for audio modes):

   # macOS
   brew install portaudio
   
   # Ubuntu/Debian
   sudo apt-get install portaudio19-dev
   
   # Windows
   # Download from http://www.portaudio.com/

Usage

Text Mode (No PortAudio Required)

export OPENAI_API_KEY=your-key
go run .

Interactive Voice Mode

export OPENAI_API_KEY=your-key
go run -tags portaudio .

Available Modes (with PortAudio)

# Interactive voice chat (default)
go run -tags portaudio . interactive

# Function calling demo (ask about weather)
go run -tags portaudio . tools

# Real-time translator (English to Spanish)
go run -tags portaudio . translator

How It Works

Architecture

                    PromptKit SDK
                         |
                         v
            +-----------------------+
            |   OpenDuplex()        |
            |   - Creates session   |
            |   - Manages WebSocket |
            +-----------------------+
                         |
         +---------------+---------------+
         |                               |
         v                               v
+------------------+           +------------------+
| Audio Capture    |           | Audio Playback   |
| (Microphone)     |           | (Speakers)       |
| 24kHz PCM16      |           | 24kHz PCM16      |
+------------------+           +------------------+
         |                               ^
         v                               |
+------------------+           +------------------+
| SendChunk()      |           | Response()       |
| - Audio chunks   |           | - Audio deltas   |
| - Text messages  |           | - Text deltas    |
+------------------+           +------------------+
         |                               ^
         v                               |
+-------------------------------------------------+
|              OpenAI Realtime API                |
|              (WebSocket Connection)             |
|                                                 |
|  - gpt-4o-realtime-preview model               |
|  - Server-side VAD (Voice Activity Detection)  |
|  - Function/Tool calling                       |
|  - Audio transcription                         |
+-------------------------------------------------+

Audio Format

OpenAI Realtime API uses:

• Sample Rate: 24kHz (24000 Hz)
• Bit Depth: 16-bit signed integer
• Channels: Mono (1 channel)
• Encoding: PCM16 (little-endian)

Code Example

package main

import (
    "context"
    "github.com/AltairaLabs/PromptKit/runtime/providers"
    "github.com/AltairaLabs/PromptKit/runtime/types"
    "github.com/AltairaLabs/PromptKit/sdk"
)

func main() {
    // Open duplex conversation
    conv, _ := sdk.OpenDuplex(
        "./openai-realtime.pack.json",
        "assistant",
        sdk.WithModel("gpt-4o-realtime-preview"),
        sdk.WithAPIKey(os.Getenv("OPENAI_API_KEY")),
        sdk.WithStreamingConfig(&providers.StreamingInputConfig{
            Config: types.StreamingMediaConfig{
                Type:       types.ContentTypeAudio,
                SampleRate: 24000,
                Channels:   1,
                Encoding:   "pcm16",
                BitDepth:   16,
                ChunkSize:  4800,
            },
            Metadata: map[string]interface{}{
                "voice":               "alloy",
                "modalities":          []string{"text", "audio"},
                "input_transcription": true,
            },
        }),
    )
    defer conv.Close()

    // Send audio chunk
    chunk := &providers.StreamChunk{
        MediaDelta: &types.MediaContent{
            MIMEType: "audio/pcm",
            Data:     &audioData, // PCM16 bytes as string
        },
    }
    conv.SendChunk(ctx, chunk)

    // Or send text
    conv.SendText(ctx, "Hello!")

    // Receive streaming response
    respCh, _ := conv.Response()
    for chunk := range respCh {
        if chunk.MediaDelta != nil {
            // Play audio
        }
        if chunk.Delta != "" {
            // Print text
        }
    }
}

Voice Options

Function Calling

The tools demo shows how to handle function calls during streaming:

// Define tools in StreamingInputConfig
Tools: []providers.StreamingToolDefinition{
    {
        Name:        "get_weather",
        Description: "Get the current weather for a location",
        Parameters: map[string]interface{}{...},
    },
},

// Handle tool calls in response
if chunk.ToolCalls != nil {
    for _, tc := range chunk.ToolCalls {
        result := executeToolCall(tc.Name, tc.Arguments)
        conv.SendToolResult(ctx, tc.ID, result)
    }
}

Troubleshooting

”OPENAI_API_KEY environment variable is required”

Set your API key:

export OPENAI_API_KEY=sk-...

“failed to initialize PortAudio”

Install PortAudio for your platform (see Prerequisites above).

No audio output

• Check your speaker/headphone volume
• Ensure the correct audio device is selected as default
• Try a different voice option

Echo/feedback issues

Use headphones to prevent the microphone from picking up speaker output.

Related Examples

• duplex-streaming - Gemini Live API streaming
• voice-chat - Traditional STT/TTS voice chat
• voice-interview - Full voice interview application

Resources

• OpenAI Realtime API Documentation
• PromptKit Streaming Documentation