obul-dtelecom

dTelecom Speech-to-Text

Production-grade real-time speech-to-text for AI agents via dTelecom's x402-enabled STT service. Features a dual-engine architecture (Parakeet-TDT for 25 European languages at 3-4x speed, Whisper for 99+ languages) with smart routing, voice activity detection, neural noise reduction, speech validation, and hallucination filtering. Through the Obul proxy, each session is paid per minute at $0.005/min — no dTelecom account or API key required.

Authentication

All requests use the obulx CLI, which handles proxy routing and authentication automatically.

Install and log in (one-time setup):

npm install -g @obul.ai/obulx
obulx login

Base URL: https://x402stt.dtelecom.org

Common Operations

Create a Transcription Session

Create and pay for a new STT session. Specify the number of minutes and target language. The response includes a session key and WebSocket URL for streaming audio.

Pricing: $0.005 per minute (minimum 5 minutes = $0.025, maximum 120 minutes = $0.60)

obulx -X POST -H "Content-Type: application/json" \
  -d '{"minutes": 5, "language": "en"}' \
  "https://x402stt.dtelecom.org/v1/session"

Response:

{
  "session_id": "abc-123-uuid",
  "session_key": "eyJ...",
  "ws_url": "wss://x402stt.dtelecom.org/v1/stream",
  "remaining_seconds": 300,
  "minutes": 5,
  "price_usd": "0.025000"
}

Extend an Active Session

Add more time to an active session without interrupting the audio stream.

Pricing: $0.005 per minute added

obulx -X POST -H "Content-Type: application/json" \
  -d '{"session_id": "abc-123-uuid", "minutes": 5}' \
  "https://x402stt.dtelecom.org/v1/session/extend"

Response:

{
  "session_id": "abc-123-uuid",
  "remaining_seconds": 600,
  "minutes_added": 5,
  "price_usd": "0.025000"
}

Check Session Status

Check the remaining time and usage of an active session. This endpoint is free.

Pricing: $0.00

obulx "https://x402stt.dtelecom.org/v1/session/{session_id}/status"

Response:

{
  "session_id": "abc-123-uuid",
  "status": "connected",
  "remaining_seconds": 245.3,
  "used_seconds": 54.7,
  "balance_seconds": 300,
  "language": "en"
}

Stream Audio via WebSocket

After creating a session, connect to the WebSocket URL with the session key. Send audio as PCM16 (16-bit little-endian, 16kHz, mono) in 20ms chunks (640 bytes). The server returns real-time transcription results.

Pricing: Included in session cost

WebSocket handshake (client sends):

{
  "type": "config",
  "language": "en",
  "session_key": "eyJ..."
}

Server ready response:

{
  "type": "ready",
  "remaining_seconds": 300
}

Transcription response (server sends for each utterance):

{
  "type": "transcription",
  "text": "Hello, how are you?",
  "start": 1.5,
  "end": 2.8,
  "confidence": 0.95,
  "is_final": true
}

Check Service Health

Verify the STT service is available. No payment required.

Pricing: $0.00

obulx "https://x402stt.dtelecom.org/health"

Endpoint Pricing Reference

Endpoint	Price	Purpose
POST /v1/session	$0.005/min	Create and pay for a new STT session
POST /v1/session/extend	$0.005/min	Add time to an active session
GET /v1/session/{id}/status	$0.00	Check remaining session time and usage
WS /v1/stream	Included	Stream audio and receive transcriptions
GET /health	$0.00	Service availability check
GET /pricing	$0.00	Retrieve current rate information

When to Use

• Real-time transcription — Stream audio and get live transcription results with confidence scores and timestamps.
• Multi-language support — Transcribe in 99+ languages with automatic engine selection (Parakeet-TDT for European languages, Whisper for others).
• Long-running sessions — Record meetings, interviews, or calls with sessions up to 120 minutes, extendable without interruption.
• Cost-effective transcription — At $0.005/min, dTelecom is 20x cheaper than x402engine transcription ($0.10/req) for audio longer than a few seconds.
• Noisy audio — Built-in VAD, noise reduction, and hallucination filtering handle real-world audio conditions.

Best Practices

• Start with 5-minute sessions — Use the minimum session length and extend as needed rather than over-purchasing time upfront.
• Use the correct audio format — Send PCM16, 16kHz, mono audio in 20ms chunks (640 bytes). Incorrect formats will produce garbled results or errors.
• Set the language parameter — While both engines support auto-detection, specifying the language improves accuracy and routes to the optimal engine.
• Monitor session expiry warnings — The server sends session_expiring messages at 60 and 10 seconds remaining. Use these to trigger automatic session extension.
• Handle reconnection — If the WebSocket disconnects, the billing clock pauses. Reconnect with the same session key to resume without losing paid time.
• Prefer Parakeet-TDT languages — For English and other European languages, the Parakeet-TDT engine is 3-4x faster with 3-5% word error rate.

Error Handling

Error	Cause	Solution
402 Payment Required	x402 payment not processed	Verify your account has sufficient balance at my.obul.ai. Run obulx login if not authenticated.
400 Bad Request	Missing or invalid parameters	Ensure minutes (5-120) and language are provided and correctly typed.
404 Not Found	Session ID does not exist	Verify the session ID is correct. Sessions expire after their purchased time runs out.
WS 4001	Config timeout or invalid config	Send the config message with valid session_key immediately after WebSocket connection.
WS 4002	Session expired or not found	Create a new session. The previous session's time has been exhausted.
WS 4003	Authentication failure	Verify the session_key matches the one returned from session creation.
WS 4004	Session already connected elsewhere	Only one WebSocket connection per session is allowed. Close the other connection first.
500 Internal Server Error	Upstream dTelecom service issue	Wait a few seconds and retry. If persistent, check /health for service status.