Streaming protocol

wss://stt.omnia-voice.com/stream
wss://stt.omnia-voice.com/v2/stream

Both endpoints speak the same protocol. The URL picks the engine; everything else is identical. For a walkthrough with full examples see the Streaming transcription guide.

Engines

	`/stream`	`/v2/stream`
Status	Generally available	Preview
Default languages	`fi-FI`, `sv-SE`	`auto`
`languages` option	Restricts recognition to the codes given	Biases recognition toward the codes given; may still switch language mid-session
Interim results	Occasional	Continuous, roughly twice per second
Finals	Short phrases, finalised quickly	Whole utterances, finalised at pauses
`language` on results	Detected code per result	Empty
`confidence` on finals	`0`	`0`
Session length	Unlimited; reconnects behind the scenes	Unlimited; reconnects behind the scenes

Connecting

Query parameters (both endpoints)

Parameter	Description
`languages`	Comma-separated BCP-47 codes, up to 10, or `auto`. Overridden by `languages` in the auth message if both are given.

Authentication, one of:

Subprotocol list ["token", "<api key>"] on the upgrade. The socket is authenticated before it opens; a bad key is refused with HTTP 401.
An auth message within 30 seconds of connecting (below).

Rejections at upgrade time: 400 for an invalid languages value, 401 for a bad key, 503 when the service is at capacity.

Client → server messages

Audio is sent as binary frames: 16 kHz, 16-bit signed little-endian PCM, mono, ideally 640 bytes (20 ms) per frame at a steady cadence. Control messages are JSON text frames:

object

Authenticate when no subprotocol was used. Must be the first message.

{
  "type": "auth",
  "apiKey": "om_xxx",
  "languages": ["fi-FI", "sv-SE"],
  "metadata": { "callId": "abc-123" }
}

languages and metadata are optional. metadata is passed through unchanged to usage webhooks and cannot be set with subprotocol auth.

object

Signal that no more audio is coming. The engine flushes its last result. Keep the socket open until you receive it, then close.

{ "type": "end" }

Server → client messages

object

Authentication succeeded and the engine is configured. Send audio after this.

{
  "type": "ready",
  "sessionId": "stt_1788786506604_8fd6cc541a02b620",
  "message": "Authenticated. Send audio as binary frames.",
  "languages": ["fi-FI", "sv-SE"],
  "audio_format": {
    "required": "PCM 16-bit signed little-endian (LINEAR16)",
    "sample_rate": 16000,
    "channels": 1,
    "chunk_size_bytes": 640,
    "chunk_interval_ms": 20
  }
}

sessionId is the same id reported in usage webhooks. languages echoes the configuration actually applied.

object

A recognition result.

{
  "type": "transcript",
  "transcript": "Moi, Kati tässä.",
  "isFinal": true,
  "confidence": 0,
  "language": "fi-FI"
}

isFinal: false results are provisional and will be replaced. isFinal: true results are settled. On /v2/stream an interim carries the cumulative text of the current utterance so far; the matching final replaces it.

object

{ "type": "error", "code": "INVALID_API_KEY", "error": "Invalid API key", "message": "Invalid API key" }

error and message carry the same text. Codes you may see:

Code	Meaning
`INVALID_API_KEY`, `API_KEY_DISABLED`, `API_KEY_EXPIRED`	Key rejected
`NO_SUBSCRIPTION`, `INSUFFICIENT_CREDITS`, `FEATURE_NOT_AVAILABLE`	Account cannot use transcription right now
`INVALID_LANGUAGES`	Bad `languages` value in the auth message
`NOT_AUTHENTICATED`	Audio or control message sent before `auth`
`AUTH_TIMEOUT`	No `auth` message within 30 seconds
`SERVICE_UNAVAILABLE`	Temporary upstream failure; reconnect

Lifecycle

Connect with the key in the subprotocol, or connect and send auth.
Wait for ready.
Send audio frames at a steady 20 ms cadence. Read transcript messages.
Send end. Wait for the last isFinal: true.
Close the socket.

Usage is reported once per session, after the socket closes, with type: "stream", the billed duration, and any metadata you attached.

Overview

Speech to text

Tools

Calls

Agents

Phone Numbers

Call Logs

Configuration

Pricing

Engines

Connecting

Client → server messages

Server → client messages

Lifecycle

​Engines

​Connecting

​Client → server messages

​Server → client messages

​Lifecycle

Engines

Connecting

Client → server messages

Server → client messages

Lifecycle