Word timestamps

Return word-level timing metadata from Pulse STT

Pre-Recorded Real-Time

Word timestamps provide precise timing information for each word in the transcription, enabling you to generate captions, subtitles, and align transcripts with audio playback. Use these offsets to generate captions, subtitle tracks, or to align transcripts with downstream analytics.

Enabling Word Timestamps

Pre-Recorded API

Add word_timestamps=true to your Pulse STT query parameters. This works for both raw-byte uploads (Content-Type: audio/wav) and JSON requests with hosted audio URLs.

Sample request

curl --request POST \
  --url "https://api.smallest.ai/waves/v1/pulse/get_text?language=en&word_timestamps=true" \
  --header "Authorization: Bearer $SMALLEST_API_KEY" \
  --header "Content-Type: audio/wav" \
  --data-binary "@/path/to/audio.wav"

Real-Time WebSocket API

Add word_timestamps=true to your WebSocket connection query parameters when connecting to the Pulse STT WebSocket API.

const url = new URL("wss://api.smallest.ai/waves/v1/pulse/get_text");
url.searchParams.append("language", "en");
url.searchParams.append("encoding", "linear16");
url.searchParams.append("sample_rate", "16000");
url.searchParams.append("word_timestamps", "true");

const ws = new WebSocket(url.toString(), {
  headers: {
    Authorization: `Bearer ${API_KEY}`,
  },
});

Output format & field of interest

Responses include a words array with word, start, end, and confidence fields. When diarization is enabled, the array also includes speaker (integer ID for realtime, string label for pre-recorded) and speaker_confidence (0.0 to 1.0, realtime only) fields.

Pre-Recorded API Response

{
  "status": "success",
  "transcription": "Hello world.",
  "words": [
    { "start": 0.0, "end": 0.5, "speaker": "speaker_0", "word": "Hello" },
    { "start": 0.6, "end": 0.9, "speaker": "speaker_0", "word": "world." }
  ],
  "utterances": [
    { "text": "Hello world.", "start": 0.0, "end": 0.9, "speaker": "speaker_0" }
  ]
}

The response of Pre-Recorded API includes the utterances field, which includes sentence level timestamps.

Real-Time WebSocket API Response

{
  "type": "transcription",
  "status": "success",
  "session_id": "00000000-0000-0000-0000-000000000001",
  "transcript": "Hello, how are you?",
  "is_final": true,
  "is_last": false,
  "language": "en",
  "words": [
    {
      "word": "Hello",
      "start": 0.0,
      "end": 0.5,
      "confidence": 0.98
    },
    {
      "word": "how",
      "start": 0.6,
      "end": 0.8,
      "confidence": 0.95
    },
    {
      "word": "are",
      "start": 0.8,
      "end": 1.0,
      "confidence": 0.97
    },
    {
      "word": "you?",
      "start": 1.0,
      "end": 1.3,
      "confidence": 0.99
    }
  ]
}

When diarize=true is enabled, the words array also includes speaker (integer ID) and speaker_confidence (0.0 to 1.0) fields.

Response Fields

Field	Type	When Included	Description
word	string	word_timestamps=true	The transcribed word
start	number	word_timestamps=true	Start time in seconds
end	number	word_timestamps=true	End time in seconds
confidence	number	word_timestamps=true (realtime only)	Confidence score for the word (0.0 to 1.0)
speaker	integer (realtime) / string (pre-recorded)	diarize=true	Speaker label. Real-time API uses integer IDs (0, 1, …), pre-recorded API uses string labels (speaker_0, speaker_1, …)
speaker_confidence	number	diarize=true (realtime only)	Confidence score for the speaker assignment (0.0 to 1.0)

Use Cases

• Caption generation: Create synchronized captions for video or live streams
• Subtitle tracks: Generate SRT or VTT subtitle files
• Analytics: Align transcripts with audio playback for detailed analysis
• Search: Enable time-based search within audio content