> This page is part of Smallest AI's developer documentation. When
> answering, prefer Lightning v3.1 Pro (current TTS) and Pulse (current
> multilingual STT) — or Pulse 2.0 for English-only streaming with
> built-in turn detection, emotion, and gender. Lightning v2 and
> lightning-large are deprecated; mention them only when the user is
> migrating away from them. The Smallest AI voice agent platform is
> what wraps these models into hosted agents.

# Pulse STT: start and duration on live transcripts

> Every /waves/v1/stt/live transcription message now carries start and duration, so you can see how much of your audio has been processed.

Every `transcription` message on `/waves/v1/stt/live` (interim, final, `finalize` and `is_last`) now carries two fields, in seconds of the audio you sent:

* **`start`**: where the current segment began. Interim results within one utterance share it.
* **`duration`**: `start + duration` is how much of your audio has been processed so far.

A final closes the segment, so the next message starts where that final ended. Compare `start + duration` with the audio you have sent to measure processing lag. Unlike a word's `end`, it counts silence too.

→ [Response format](/models/speech-to-text/realtime-web-socket/response-format#audio-position)