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Class: AzureSpeechTTSProvider

Defined in: packages/agentos/src/io/speech/providers/AzureSpeechTTSProvider.ts:211

Text-to-speech provider that uses the Azure Cognitive Services Speech REST API.

SSML Generation​

Azure's TTS REST endpoint requires SSML (Speech Synthesis Markup Language) as the request body — it does not accept plain text. This provider generates minimal SSML via buildSsml() that wraps the input text in <speak> and <voice> elements. Special XML characters in the text are escaped via escapeXml() to prevent malformed XML.

X-Microsoft-OutputFormat Options​

The X-Microsoft-OutputFormat header controls the audio encoding. This provider uses 'audio-24khz-96kbitrate-mono-mp3' which provides:

  • 24 kHz sample rate (high quality for speech)
  • 96 kbps bitrate (good balance of quality and file size)
  • Mono channel (sufficient for speech synthesis)
  • MP3 format (universally supported)

Other available formats include:

  • 'audio-16khz-128kbitrate-mono-mp3' — Lower sample rate, higher bitrate
  • 'audio-24khz-160kbitrate-mono-mp3' — Higher bitrate for better quality
  • 'riff-24khz-16bit-mono-pcm' — Uncompressed WAV
  • 'ogg-24khz-16bit-mono-opus' — Opus codec in OGG container

See​

Voice Listing​

The listAvailableVoices method fetches the full list of neural voices available in the configured Azure region via GET /cognitiveservices/voices/list. Results are mapped to the normalized SpeechVoice shape.

Example​

const provider = new AzureSpeechTTSProvider({
  key: process.env.AZURE_SPEECH_KEY!,
  region: 'eastus',
  defaultVoice: 'en-US-GuyNeural',
});
const result = await provider.synthesize('Hello world');
// result.audioBuffer contains MP3 bytes
// result.mimeType === 'audio/mpeg'

Implements​

Constructors​

Constructor​

new AzureSpeechTTSProvider(config): AzureSpeechTTSProvider

Defined in: packages/agentos/src/io/speech/providers/AzureSpeechTTSProvider.ts:246

Creates a new AzureSpeechTTSProvider.

Parameters​

config​

AzureSpeechTTSProviderConfig

Provider configuration including the subscription key, region, and optional default voice.

Returns​

AzureSpeechTTSProvider

Example​

const provider = new AzureSpeechTTSProvider({
  key: 'your-azure-subscription-key',
  region: 'westeurope',
  defaultVoice: 'de-DE-ConradNeural',
});

Properties​

displayName​

readonly displayName: "Azure Speech (TTS)" = 'Azure Speech (TTS)'

Defined in: packages/agentos/src/io/speech/providers/AzureSpeechTTSProvider.ts:216

Human-readable display name for UI and logging.

Implementation of​

TextToSpeechProvider.displayName

id​

readonly id: "azure-speech-tts" = 'azure-speech-tts'

Defined in: packages/agentos/src/io/speech/providers/AzureSpeechTTSProvider.ts:213

Unique provider identifier used for registration and resolution.

Implementation of​

TextToSpeechProvider.id

supportsStreaming​

readonly supportsStreaming: true = true

Defined in: packages/agentos/src/io/speech/providers/AzureSpeechTTSProvider.ts:223

Marked as streaming-capable because the provider can be used within a streaming pipeline — though the actual HTTP request is a single synchronous call that returns the complete audio buffer.

Implementation of​

TextToSpeechProvider.supportsStreaming

Methods​

getProviderName()​

getProviderName(): string

Defined in: packages/agentos/src/io/speech/providers/AzureSpeechTTSProvider.ts:261

Returns the human-readable provider name.

Returns​

string

The display name string 'Azure Speech (TTS)'.

Example​

provider.getProviderName(); // 'Azure Speech (TTS)'

Implementation of​

TextToSpeechProvider.getProviderName

listAvailableVoices()​

listAvailableVoices(): Promise<SpeechVoice[]>

Defined in: packages/agentos/src/io/speech/providers/AzureSpeechTTSProvider.ts:353

Retrieves the list of available neural voices from the Azure region.

Fetches from GET /cognitiveservices/voices/list and maps each entry to the normalized SpeechVoice shape. The list includes all neural and standard voices available in the configured region.

Returns​

Promise<SpeechVoice[]>

A promise resolving to an array of normalized voice entries.

Throws​

When the Azure API returns a non-2xx status code (e.g. invalid key, network error).

Example​

const voices = await provider.listAvailableVoices();
const englishVoices = voices.filter(v => v.lang.startsWith('en-'));
console.log(`Found ${englishVoices.length} English voices`);

Implementation of​

TextToSpeechProvider.listAvailableVoices

synthesize()​

synthesize(text, options?): Promise<SpeechSynthesisResult>

Defined in: packages/agentos/src/io/speech/providers/AzureSpeechTTSProvider.ts:288

Synthesizes speech from plain text using the Azure TTS REST endpoint.

The text is wrapped in SSML, sent to Azure, and the response audio buffer (MP3 format) is returned along with metadata.

Parameters​

text​

string

The plain-text utterance to convert to audio. XML special characters are automatically escaped.

options?​

SpeechSynthesisOptions = {}

Optional synthesis settings. Use options.voice to override the default voice with any valid Azure voice short-name.

Returns​

Promise<SpeechSynthesisResult>

A promise resolving to the MP3 audio buffer and metadata.

Throws​

When the Azure API returns a non-2xx status code. Common causes: invalid subscription key (401), region mismatch (404), invalid SSML (400), or quota exceeded (429).

Example​

const result = await provider.synthesize('Guten Tag!', {
  voice: 'de-DE-ConradNeural',
});
fs.writeFileSync('output.mp3', result.audioBuffer);

Implementation of​

TextToSpeechProvider.synthesize