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Message Protocol

Complete WebSocket message protocol reference.

Client → Server Messages​

1. Audio Data (Binary)​

Send raw PCM audio bytes:

ws.send(audioBuffer);  // ArrayBuffer or Buffer

Format: Raw 16-bit PCM audio data

2. Audio Data (JSON)​

{
  "type": "audio",
  "data": "base64_encoded_pcm_audio"
}

3. Configuration​

{
  "type": "configure",
  "sample_rate": 16000,
  "language": "en",
  "interim_results": true
}

4. End of Speech​

{
  "type": "end_of_speech"
}

Signal end of utterance to get final result immediately.

5. End of Session​

{
  "type": "end_of_session"
}

Gracefully close session.

Server → Client Messages​

1. Partial Transcript​

{
  "type": "partial",
  "text": "Hello how are",
  "confidence": 0.85,
  "timestamp": 1642089600.5,
  "is_final": false
}

Interim result that may change.

2. Final Transcript​

{
  "type": "final",
  "text": "Hello, how are you doing today?",
  "confidence": 0.95,
  "start": 0.0,
  "end": 2.5,
  "timestamp": 1642089603.0,
  "is_final": true
}

Confirmed result that won't change.

3. Error​

{
  "type": "error",
  "error": "Invalid audio format",
  "error_code": "INVALID_AUDIO_FORMAT"
}

4. Session Info​

{
  "type": "session_info",
  "session_id": "session_abc123",
  "language": "en",
  "sample_rate": 16000
}

Message Flow Example​

Client                          Server
  |                               |
  |-- Connect WebSocket ---------->|
  |<-- session_info ---------------|
  |                               |
  |-- audio chunk (binary) ------->|
  |-- audio chunk (binary) ------->|
  |<-- partial: "Hello" -----------|
  |-- audio chunk (binary) ------->|
  |<-- partial: "Hello how" -------|
  |-- audio chunk (binary) ------->|
  |<-- partial: "Hello how are" ---|
  |-- end_of_speech -------------->|
  |<-- final: "Hello, how are..." -|
  |                               |
  |-- end_of_session ------------->|
  |-- Close WebSocket ------------>|