StartSpeechSynthesisStream

Source: src/AWS/Polly/StartSpeechSynthesisStream.ts

Runtime binding for polly:StartSpeechSynthesisStream — bidirectional streaming synthesis: send text incrementally as TextEvents on the input ActionStream and receive AudioEvent chunks on the output EventStream as they become available.

The binding takes no arguments and grants the function polly:StartSpeechSynthesisStream. Provide the implementation with Effect.provide(AWS.Polly.StartSpeechSynthesisStreamHttp).

NOTE: the distilled HTTP transport does not yet support bidirectional (input) event-stream request bodies — a live call currently hangs waiting for response headers (probed 2026-07; same transport gap leaves transcribe-streaming and lex StartConversation unbound). Prefer SynthesizeSpeech (request-response) until distilled core ships event-stream request support.

Streaming Synthesis

// init
const startSpeechSynthesisStream =
  yield* AWS.Polly.StartSpeechSynthesisStream();

// runtime
const result = yield* startSpeechSynthesisStream({
  Engine: "generative",
  OutputFormat: "mp3",
  VoiceId: "Matthew",
  ActionStream: Stream.make(
    { TextEvent: { Text: "Hello from Alchemy." } },
    { CloseStreamEvent: {} },
  ),
});
const events = yield* Stream.runCollect(result.EventStream!);
const audioBytes = Array.from(events)
  .flatMap((event) => (event.AudioEvent?.AudioChunk ? [event.AudioEvent.AudioChunk] : []))
  .reduce((total, chunk) => total + chunk.length, 0);