kotoba-technologies/kotoba-stt/v1/speech-to-text

Endpoint: POST https://fal.run/kotoba-technologies/kotoba-stt/v1/speech-to-text

Overview: Upload an audio or video file of up to two minutes and receive the transcript in a single JSON response, with optional per-word timestamps, speaker attribution and the audio duration. The language is set per request with the language parameter (ja by default; see the table below). Send the audio as a multipart file upload (file) or, as the Playground does, as a JSON body with an audio_url (an https URL on fal's CDN or a base64 data: URI).

Use cases

• Voice memos, call segments, and short recordings.
• Subtitles and captions for short clips.
• Longer recordings (meetings, interviews, podcasts) split into chunks of up to two minutes.

Technical specifications

• Input: one audio or video file per request (wav, mp3, m4a, mp4, webm, ogg, flac, aac, or raw PCM), up to 120 seconds of audio; longer files are rejected. Recommended: 24 kHz, mono.
• Output: JSON with the transcript, word-level timestamps (when requested), and the audio duration.
• Options: word timestamps (with_timestamps), speaker diarization (diarization).
• Speaker diarization: diarization=true attributes each word to a speaker (speaker_id: speaker_1, speaker_2, …, numbered in order of first appearance). Word times are null unless with_timestamps=true is also set. Beta: speaker attribution is produced by the model and can differ between runs on the same audio, for example a short turn merged into its neighbour; the transcript itself is unaffected. Works for every supported language; a word the model could not attribute has speaker_id: null. words is filled when either flag is set. A deployment whose model has no speaker tokens rejects the request.
• Client: any HTTP client, or the Kotoba Python SDK (client.asr.transcribe, 0.2.0+; diarization=True from 0.2.3).
• Supported languages — pass the code in the language parameter exactly as written (lowercase). Any other value returns an unsupported_language error.

Example request

curl -X POST https://fal.run/kotoba-technologies/kotoba-stt/v1/speech-to-text \
-H "Authorization: Key $FAL_KEY" \
-F file=@clip.wav -F language=ja -F with_timestamps=true

Example response

{
"language_code": "ja",
"language_probability": 1.0,
"text": "おはようございます。今日は水曜日です。",
"words": [
  {"text": "おはようございます", "type": "word", "start": 0.12, "end": 0.98},
  {"text": "今日は", "type": "word", "start": 1.10, "end": 1.42}
],
"audio_duration_secs": 8.0
}

language_code echoes the language used for the request; language_probability is 1.0 when a language was supplied and 0.0 otherwise (the endpoint does not detect languages). words is filled when with_timestamps=true or diarization=true.

Example response with diarization=true and with_timestamps=true (two speakers)

{
"language_code": "ja",
"language_probability": 1.0,
"text": "おはようございます。
はい、わかりました。",
"words": [
  {"text": "おはようございます", "type": "word", "start": 0.00, "end": 1.40, "speaker_id": "speaker_1"},
  {"text": "。", "type": "word", "start": 1.40, "end": 1.42, "speaker_id": "speaker_1"},
  {"text": "はい", "type": "word", "start": 4.80, "end": 5.10, "speaker_id": "speaker_2"},
  {"text": "、わかりました。", "type": "word", "start": 5.10, "end": 6.10, "speaker_id": "speaker_2"}
],
"audio_duration_secs": 9.0
}

With diarization on, text has a line break at each speaker change. With diarization=true alone, speaker_id is set and start / end are null.

Example (Python)

import os
import requests

r = requests.post(
  "https://fal.run/kotoba-technologies/kotoba-stt/v1/speech-to-text",
  headers={"Authorization": f"Key {os.environ['FAL_KEY']}"},
  files={"file": open("clip.wav", "rb")},
  data={"language": "ja", "with_timestamps": "true"},
)
print(r.json()["text"])

Example (Python SDK)

import kotoba

client = kotoba.KotobaClient()  # KOTOBA_API_KEY + KOTOBA_ASR_REST_URL from the environment
result = client.asr.transcribe("clip.wav", language="ja", with_timestamps=True)
print(result.text)
for segment in result.segments or []:
  print(segment.start, segment.end, segment.text)

# Speaker diarization (kotoba-sdk 0.2.3+): consecutive words grouped by speaker, in reading order
result = client.asr.transcribe("meeting.wav", language="ja", diarization=True, with_timestamps=True)
for u in result.utterances or []:
  print(f"{u.start:6.2f}  {u.speaker_id}: {u.text}")

Pricing: $0.25 per hour of input audio (unit: second of input audio, $0.0000694 per second).

Using the Kotoba Python SDK

The kotoba-sdk package (PyPI, Python 3.10+, version 0.2.3 or newer) covers all four apps. It sends the fal key with fal's Authorization: Key scheme automatically for fal.run URLs, so use the fal key as the API key and point the per-route URLs at the apps.

pip install kotoba-sdk
export KOTOBA_API_KEY=<fal key>
export KOTOBA_ASR_REST_URL=https://fal.run/kotoba-technologies/kotoba-stt/v1
export KOTOBA_ASR_URL=wss://fal.run/kotoba-technologies/kotoba-streaming-stt/v1/realtime
export KOTOBA_TTS_URL=wss://fal.run/kotoba-technologies/kotoba-tts/v2/tts/ws
export KOTOBA_S2ST_URL=wss://fal.run/kotoba-technologies/kotoba-sts/v1/realtime_voice

An app that has been idle may boot a GPU runner on the first request, which can take a few minutes. Allow for that in the request timeout or retry the first request; the SDK's default timeouts are 30 seconds for HTTP requests (KotobaClient(timeout=...)) and 15 seconds for the WebSocket handshake.