OpenAI Realtime voice

The OpenAIRealtimeVoice class provides real-time voice interaction capabilities using OpenAI's WebSocket-based API. It supports real time speech to speech, voice activity detection, and event-based audio streaming.

Usage example

import { OpenAIRealtimeVoice } from '@mastra/voice-openai-realtime'
import { playAudio, getMicrophoneStream } from '@mastra/node-audio'

// Initialize with default configuration using environment variables
const voice = new OpenAIRealtimeVoice()

// Or initialize with specific configuration
const voiceWithConfig = new OpenAIRealtimeVoice({
  apiKey: 'your-openai-api-key',
  model: 'gpt-5.1-realtime-preview-2024-12-17',
  speaker: 'alloy', // Default voice
})

voiceWithConfig.updateSession({
  turn_detection: {
    type: 'server_vad',
    threshold: 0.6,
    silence_duration_ms: 1200,
  },
})

// Establish connection
await voice.connect()

// Set up event listeners
voice.on('speaker', ({ audio }) => {
  // Handle audio data (Int16Array) pcm format by default
  playAudio(audio)
})

voice.on('writing', ({ text, role }) => {
  // Handle transcribed text
  console.log(`${role}: ${text}`)
})

// Convert text to speech
await voice.speak('Hello, how can I help you today?', {
  speaker: 'echo', // Override default voice
})

// Process audio input
const microphoneStream = getMicrophoneStream()
await voice.send(microphoneStream)

// When done, disconnect
voice.connect()

Configuration

Constructor options

<PropertiesTable content={[ { name: 'model', type: 'string', description: 'The model ID to use for real-time voice interactions.', isOptional: true, defaultValue: "'gpt-5.1-realtime-preview-2024-12-17'", }, { name: 'apiKey', type: 'string', description: 'OpenAI API key. Falls back to OPENAI_API_KEY environment variable.', isOptional: true, }, { name: 'speaker', type: 'string', description: 'Default voice ID for speech synthesis.', isOptional: true, defaultValue: "'alloy'", }, ]} />

Voice Activity Detection (VAD) Configuration

<PropertiesTable content={[ { name: 'type', type: 'string', description: 'Type of VAD to use. Server-side VAD provides better accuracy.', isOptional: true, defaultValue: "'server_vad'", }, { name: 'threshold', type: 'number', description: 'Speech detection sensitivity (0.0-1.0).', isOptional: true, defaultValue: '0.5', }, { name: 'prefix_padding_ms', type: 'number', description: 'Milliseconds of audio to include before speech is detected.', isOptional: true, defaultValue: '1000', }, { name: 'silence_duration_ms', type: 'number', description: 'Milliseconds of silence before ending a turn.', isOptional: true, defaultValue: '1000', }, ]} />

Methods

connect()

Establishes a connection to the OpenAI Realtime service. Must be called before using speak, listen, or send functions.

<PropertiesTable content={[ { name: 'returns', type: 'Promise<void>', description: 'Promise that resolves when the connection is established.', }, ]} />

speak()

Emits a speaking event using the configured voice model. Can accept either a string or a readable stream as input.

<PropertiesTable content={[ { name: 'input', type: 'string | NodeJS.ReadableStream', description: 'Text or text stream to convert to speech.', isOptional: false, }, { name: 'options', type: 'Options', description: 'Configuration options.', isOptional: true, properties: [ { type: 'Options', parameters: [ { name: 'speaker', type: 'string', description: 'Voice ID to use for this specific speech request.', isOptional: true, defaultValue: "Constructor's speaker value", }, ], }, ], }, ]} />

Returns: Promise<void>

listen()

Processes audio input for speech recognition. Takes a readable stream of audio data and emits a 'listening' event with the transcribed text.

<PropertiesTable content={[ { name: 'audioData', type: 'NodeJS.ReadableStream', description: 'Audio stream to transcribe.', isOptional: false, }, ]} />

Returns: Promise<void>

send()

Streams audio data in real-time to the OpenAI service for continuous audio streaming scenarios like live microphone input.

<PropertiesTable content={[ { name: 'audioData', type: 'NodeJS.ReadableStream', description: 'Audio stream to send to the service.', isOptional: false, }, ]} />

Returns: Promise<void>

updateConfig()

Updates the session configuration for the voice instance. This can be used to modify voice settings, turn detection, and other parameters.

<PropertiesTable content={[ { name: 'sessionConfig', type: 'Realtime.SessionConfig', description: 'New session configuration to apply.', isOptional: false, }, ]} />

Returns: void

addTools()

Adds a set of tools to the voice instance. Tools allow the model to perform additional actions during conversations. When OpenAIRealtimeVoice is added to an Agent, any tools configured for the Agent will automatically be available to the voice interface.

<PropertiesTable content={[ { name: 'tools', type: 'ToolsInput', description: 'Tools configuration to equip.', isOptional: true, }, ]} />

Returns: void

close()

Disconnects from the OpenAI Realtime session and cleans up resources. Should be called when you're done with the voice instance.

Returns: void

getSpeakers()

Returns a list of available voice speakers.

Returns: Promise<Array<{ voiceId: string; [key: string]: any }>>

on()

Registers an event listener for voice events.

<PropertiesTable content={[ { name: 'event', type: 'string', description: 'Name of the event to listen for.', isOptional: false, }, { name: 'callback', type: 'Function', description: 'Function to call when the event occurs.', isOptional: false, }, ]} />

Returns: void

off()

Removes a previously registered event listener.

<PropertiesTable content={[ { name: 'event', type: 'string', description: 'Name of the event to stop listening to.', isOptional: false, }, { name: 'callback', type: 'Function', description: 'The specific callback function to remove.', isOptional: false, }, ]} />

Returns: void

Events

The OpenAIRealtimeVoice class emits the following events:

<PropertiesTable content={[ { name: 'speaking', type: 'event', description: 'Emitted when audio data is received from the model. Callback receives { audio: Int16Array }.', }, { name: 'writing', type: 'event', description: 'Emitted when transcribed text is available. Callback receives { text: string, role: string }.', }, { name: 'error', type: 'event', description: 'Emitted when an error occurs. Callback receives the error object.', }, ]} />

OpenAI Realtime Events

You can also listen to OpenAI Realtime utility events by prefixing with 'openAIRealtime:':

<PropertiesTable content={[ { name: 'openAIRealtime:conversation.created', type: 'event', description: 'Emitted when a new conversation is created.', }, { name: 'openAIRealtime:conversation.interrupted', type: 'event', description: 'Emitted when a conversation is interrupted.', }, { name: 'openAIRealtime:conversation.updated', type: 'event', description: 'Emitted when a conversation is updated.', }, { name: 'openAIRealtime:conversation.item.appended', type: 'event', description: 'Emitted when an item is appended to the conversation.', }, { name: 'openAIRealtime:conversation.item.completed', type: 'event', description: 'Emitted when an item in the conversation is completed.', }, ]} />

Available voices

The following voice options are available:

• alloy: Neutral and balanced
• ash: Clear and precise
• ballad: Melodic and smooth
• coral: Warm and friendly
• echo: Resonant and deep
• sage: Calm and thoughtful
• shimmer: Bright and energetic
• verse: Versatile and expressive

Notes

• API keys can be provided via constructor options or the OPENAI_API_KEY environment variable
• The OpenAI Realtime Voice API uses WebSockets for real-time communication
• Server-side Voice Activity Detection (VAD) provides better accuracy for speech detection
• All audio data is processed as Int16Array format
• The voice instance must be connected with connect() before using other methods
• Always call close() when done to properly clean up resources
• Memory management is handled by OpenAI Realtime API