voice.speak() ✅

The speak() method is a core function available in all Kastrax voice providers that converts text to speech. It takes text input and returns an audio stream that can be played or saved.

Usage Example ✅


import { OpenAIVoice } from "@kastrax/voice-openai";
// Initialize a voice provider
const voice = new OpenAIVoice({
  speaker: "alloy", // Default voice
});
// Basic usage with default settings
const audioStream = await voice.speak("Hello, world!");
// Using a different voice for this specific request
const audioStreamWithDifferentVoice = await voice.speak("Hello again!", {
  speaker: "nova",
});
// Using provider-specific options
const audioStreamWithOptions = await voice.speak("Hello with options!", {
  speaker: "echo",
  speed: 1.2, // OpenAI-specific option
});
// Using a text stream as input
import { Readable } from "stream";
const textStream = Readable.from(["Hello", " from", " a", " stream!"]);
const audioStreamFromTextStream = await voice.speak(textStream);

Parameters ✅

input:

string | NodeJS.ReadableStream

Text to convert to speech. Can be a string or a readable stream of text.

options?:

object

Options for speech synthesis

options.speaker?:

string

Voice ID to use for this specific request. Overrides the default speaker set in the constructor.

Return Value ✅

Returns a Promise<NodeJS.ReadableStream | void> where:

NodeJS.ReadableStream: A stream of audio data that can be played or saved
void: When using a realtime voice provider that emits audio through events instead of returning it directly

Provider-Specific Options ✅

Each voice provider may support additional options specific to their implementation. Here are some examples:

OpenAI

options.speed?:

number

= 1.0

Speech speed multiplier. Values between 0.25 and 4.0 are supported.

ElevenLabs

options.stability?:

number

= 0.5

Voice stability. Higher values result in more stable, less expressive speech.

options.similarity_boost?:

number

= 0.75

Voice clarity and similarity to the original voice.

Google

options.languageCode?:

string

Language code for the voice (e.g., 'en-US').

options.audioConfig?:

object

= { audioEncoding: 'LINEAR16' }

Audio configuration options from Google Cloud Text-to-Speech API.

Murf

options.properties.rate?:

number

Speech rate multiplier.

options.properties.pitch?:

number

Voice pitch adjustment.

options.properties.format?:

'MP3' | 'WAV' | 'FLAC' | 'ALAW' | 'ULAW'

Output audio format.

Realtime Voice Providers ✅

When using realtime voice providers like OpenAIRealtimeVoice, the speak() method behaves differently:

Instead of returning an audio stream, it emits a ‘speaking’ event with the audio data
You need to register an event listener to receive the audio chunks


import { OpenAIRealtimeVoice } from "@kastrax/voice-openai-realtime";
import Speaker from "@kastrax/node-speaker";
 
const speaker = new Speaker({
  sampleRate: 24100,  // Audio sample rate in Hz - standard for high-quality audio on MacBook Pro
  channels: 1,        // Mono audio output (as opposed to stereo which would be 2)
  bitDepth: 16,       // Bit depth for audio quality - CD quality standard (16-bit resolution)
});
 
const voice = new OpenAIRealtimeVoice();
await voice.connect();
// Register event listener for audio chunks
voice.on("speaker", (stream) => {
  // Handle audio chunk (e.g., play it or save it)
  stream.pipe(speaker)
});
// This will emit 'speaking' events instead of returning a stream
await voice.speak("Hello, this is realtime speech!");

Using with CompositeVoice ✅

When using CompositeVoice, the speak() method delegates to the configured speaking provider:


import { CompositeVoice } from "@kastrax/core/voice";
import { OpenAIVoice } from "@kastrax/voice-openai";
import { PlayAIVoice } from "@kastrax/voice-playai";
const voice = new CompositeVoice({
  speakProvider: new PlayAIVoice(),
  listenProvider: new OpenAIVoice(),
});
// This will use the PlayAIVoice provider
const audioStream = await voice.speak("Hello, world!");

Notes ✅

The behavior of speak() may vary slightly between providers, but all implementations follow the same basic interface.
When using a realtime voice provider, the method might not return an audio stream directly but instead emit a ‘speaking’ event.
If a text stream is provided as input, the provider will typically convert it to a string before processing.
The audio format of the returned stream depends on the provider. Common formats include MP3, WAV, and OGG.
For best performance, consider closing or ending the audio stream when you’re done with it.