HTTP vs. WebSocket protocols

Every TTS and STT model is reachable over both HTTP and WebSocket. The URL stays the same; only the protocol changes. The snippets on this page use SLNG_API_KEY as a placeholder. Replace it with an SLNG key from app.slng.ai/api-keys before running the code.

At a Glance

	HTTP	WebSocket
Flow	Request → wait → complete response	Open connection → stream both ways
Latency	200–500 ms	Sub-100 ms
Best for	Batch jobs, file conversion	Voice agents, live transcription
Complexity	One `curl` call	Connection lifecycle to manage

How Each Protocol Works

HTTP
WebSocket

You send a request and get back the full result once processing finishes.Use HTTP when you:

Generate audio files for download or storage
Transcribe pre-recorded audio files
Want the simplest possible integration
Don’t need real-time streaming

curl https://api.slng.ai/v1/tts/slng/deepgram/aura:2-en \
  -H "Authorization: Bearer SLNG_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{ "model": "aura-2-thalia-en", "text": "Hello from HTTP!" }' \
  --output hello.wav

See complete examples: TTS over HTTP · STT over HTTP

You open a persistent connection and stream data in both directions.Use WebSocket when you:

Build voice agents (STT + LLM + TTS in a loop)
Need real-time transcription from a microphone
Want the lowest possible latency
Stream audio continuously

const ws = new WebSocket("wss://api.slng.ai/v1/tts/slng/deepgram/aura:2-en");

ws.onopen = () => {
  ws.send(JSON.stringify({ type: "text", text: "Hello from WebSocket!" }));
};

ws.onmessage = (event) => {
  if (event.data instanceof ArrayBuffer) {
    playAudio(event.data); // Stream audio as it arrives
  }
};

See complete examples: TTS over WebSocket · STT over WebSocket

WebSocket Best Practices

WebSocket connections are stateful. You need to handle the lifecycle:

Reconnect with backoff. If the connection drops, retry with exponential delay (1s, 2s, 4s… up to 30s).
Handle binary and text frames. Audio arrives as binary ArrayBuffer; control messages come as JSON text.
Send a close frame when you’re done so the server releases resources.

Which Protocol for Which Use Case?

Use case	Protocol	Why
Convert a script to an audio file	HTTP	One request, one file. Simple
Transcribe a batch of recordings	HTTP	Upload each file, get results
Voice agent (phone or web)	WebSocket	Real-time STT→LLM→TTS loop
Live captioning / transcription	WebSocket	Stream mic audio, get text back
Generate a voiceover for a video	HTTP	No real-time requirement

Next Steps

TTS over HTTP

Generate audio files from text with simple HTTP requests.

TTS over WebSocket

Stream audio in real-time with interruption support.

STT over HTTP

Transcribe pre-recorded audio files.

STT over WebSocket

Transcribe live audio from a microphone.

Get started

Text-to-Speech

Speech-to-Text

Managed Agents

Integrations

SDKs & Tools

Reference

At a Glance

How Each Protocol Works

WebSocket Best Practices

Which Protocol for Which Use Case?

Next Steps

TTS over HTTP

TTS over WebSocket

STT over HTTP

STT over WebSocket

​At a Glance

​How Each Protocol Works

​WebSocket Best Practices

​Which Protocol for Which Use Case?

​Next Steps

TTS over HTTP

TTS over WebSocket

STT over HTTP

STT over WebSocket

At a Glance

How Each Protocol Works

WebSocket Best Practices

Which Protocol for Which Use Case?

Next Steps