# Fast mode Fast mode provides speech synthesis for complete text inputs. The audio streams back in the same HTTP response, so playback can start before synthesis finishes. ## Capabilities - Single-call plain text synthesis, up to 4,000 characters - Streamed raw PCM audio - Voice, speed, and volume controls - Optimized for prompts, IVR, notifications, UI read-out, and short narration ## Speech synthesis Use this endpoint to convert text to speech: **`POST /aiservices/tts/synthesize`** Include your [Zoom AI Services credentials](/docs/ai-services/auth/) and `Content-Type: application/json`. If you send the optional `Z-Account-Id` and `Z-User-Id` headers, they must match the authenticated account and user. ### Example request (cURL) ```shell curl --fail-with-body --no-buffer \ https://api.zoom.us/v2/aiservices/tts/synthesize \ -H "Authorization: Bearer $TOKEN" \ -H "Content-Type: application/json" \ --dump-header hello.headers \ --output hello.pcm \ -d '{ "input": "Hello everyone, welcome to Zoom AI Services.", "voice": "jenna", "speed": 1.0, "volume": 1.0, "response_format": "pcm_44100" }' ``` On success, `hello.pcm` contains the audio and `hello.headers` contains the `x-zm-trackingid` header. Check curl's exit status and the HTTP status before you use the file: an error writes a JSON body to the file, and an interrupted stream leaves partial audio. ### Request fields Only `input` is required. All fields are top-level properties; there is no `config` object. | Field | Type | Required | Default | Description | | ----------------- | ------ | -------- | ----------- | ---------------------------------------------------------------------------------------------------- | | `input` | string | Yes | — | Non-empty UTF-8 plain text, up to 4,000 Unicode code points. Whitespace-only input is rejected. | | `voice` | string | No | `jenna` | Case-insensitive [voice ID](/docs/ai-services/tts/#language-and-voices). | | `speed` | number | No | `1.0` | Speaking rate multiplier, from `0.5` to `2.0` inclusive. `1.0` is the voice's normal rate. | | `volume` | number | No | `1.0` | Volume multiplier, greater than `0` and up to `10` inclusive. `1.0` is the voice's normal volume. | | `response_format` | string | No | `pcm_44100` | Only `pcm_44100` is supported. Other values, including `pcm_16000`, return `400 UNSUPPORTED_FORMAT`. | The request body must be a single UTF-8 JSON object of up to 32 KiB (32,768 bytes). Characters are Unicode code points, including spaces and punctuation, and input is never truncated. Malformed JSON, a missing or empty `input`, wrong types, and out-of-range values return `400 INVALID_INPUT`. To use a default, omit the field. The API treats `input` as plain text, so SSML tags are read aloud rather than interpreted. ### Response (200) ```plaintext HTTP/1.1 200 OK Content-Type: audio/pcm;rate=44100;bits=16;channels=1;encoding=signed-int;endian=little Transfer-Encoding: chunked Cache-Control: no-store x-zm-trackingid: req_123 ``` The audio is signed 16-bit little-endian mono PCM at 44,100 Hz (88,200 bytes per second), with no WAV header. Set these values explicitly when you play or convert the audio. The response has no `Content-Length`. HTTP/1.1 responses use chunked transfer encoding. Network reads don't always end on a 16-bit sample boundary, so carry incomplete samples over to the next read. The server validates the request before it sends `200`, and sends `200` as soon as the first audio is ready. A `200` status means streaming started; synthesis succeeded only if the response body ends normally. ## Handle errors and interruptions If the request fails before streaming starts, the server returns an HTTP error status and a JSON body: ```json { "code": 400, "reason": "UNSUPPORTED_VOICE", "message": "Unsupported voice", "metadata": {} } ``` | HTTP status | Reason | Handling | | ----------- | ----------------------------------------- | -------------------------------------------------------------------------------------- | | `400` | `INVALID_INPUT` | Correct the request body, input, speed, or volume. | | `400` | `UNSUPPORTED_VOICE` | Use a [supported voice](/docs/ai-services/tts/#language-and-voices). | | `400` | `UNSUPPORTED_FORMAT` | Use `pcm_44100`. | | `400` | `TEXT_TOO_LONG` | Reduce the input to at most 4,000 Unicode code points. | | `401` | Authentication error | Check your API key or JWT. | | `402` | `QUOTA_EXCEEDED` | Your API key reached its credit limit. Raise the limit or wait until the limit resets. | | `403` | `IDENTITY_MISMATCH` or `MISSING_IDENTITY` | Check that `Z-Account-Id` and `Z-User-Id` match your credentials. | | `413` | `PAYLOAD_TOO_LARGE` | Reduce the request body to 32,768 bytes or less. | | `415` | `UNSUPPORTED_MEDIA` | Use `Content-Type: application/json`. | | `429` | `RATE_LIMIT_EXCEEDED` | Wait for the time in `Retry-After`, then retry. | | `500` | `INTERNAL_ERROR` | Report the failure with its tracking ID. | | `503` | `SERVICE_UNAVAILABLE` | Retry after 10 seconds, as given in `Retry-After` and `metadata.retry_after_seconds`. | After streaming starts, the status can't change. If synthesis fails mid-stream, the server ends the response abnormally instead of sending JSON: an HTTP/1.1 response ends without its final chunk, and an HTTP/2 stream is reset. Treat this as a failure and don't use the partial audio as a complete result. Retry temporary failures as new requests, using exponential backoff with jitter and honoring `Retry-After`. A retry synthesizes the text from the beginning, so account for audio you've already played. You can cancel a request by closing the connection. The service then stops synthesis. Cancellation doesn't support pause or resume. ## Request tracking Every response includes an `x-zm-trackingid` header. For support requests, keep this value, the approximate request time, and whether the response completed, failed, or was cancelled.