Stream live audio to Deepgram over WebSocket for real-time speech-to-text with interim and final results

Documented steps

1. Create a Deepgram API key. For browser or untrusted clients, mint a temporary/scoped token server-side rather than shipping the raw key.
2. Open a WebSocket to wss://api.deepgram.com/v1/listen.
3. Send header Authorization: Token <DEEPGRAM_API_KEY> for a standard key, or Authorization: Bearer <JWT> for a temporary token.
4. Set query params: model=nova-3 (omitting model falls back to the older default base-general), language=en-US or another BCP-47 tag, encoding (e.g. linear16, opus) and sample_rate in Hz.
5. Add interim_results=true to receive partial hypotheses (is_final:false) before finalized segments — it defaults to false.
6. Add endpointing=<ms> to control how much silence closes an utterance. The default is only 10 ms; conversational audio usually wants 300-500 ms. endpointing=false disables it.
7. Add smart_format=true to auto-format currency, phone numbers, dates and emails (default false).
8. Stream raw binary audio frames over the socket as captured, sized consistently with your encoding and sample rate.
9. During silence send the text control frame {"type":"KeepAlive"} every 3-5 seconds to avoid the 10-second idle timeout.
10. Read incoming JSON messages with type Results: use channel.alternatives[0].transcript plus is_final, speech_final, confidence and words[]. Accumulate on is_final rather than relying on speech_final alone.
11. To flush buffered audio mid-stream without closing, send {"type":"Finalize"}; the server replies with a Results message tagged from_finalize:true.
12. To end cleanly send {"type":"CloseStream"}; the server drains, emits a final Metadata message (request_id, sha256, created, duration, channels) and closes.
13. Verify against the official docs: https://developers.deepgram.com/reference/speech-to-text/listen-streaming , https://developers.deepgram.com/docs/keep-alive , https://developers.deepgram.com/docs/finalize and https://developers.deepgram.com/docs/close-stream