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LinTO-STT-Kaldi

LinTO-STT-Kaldi is an API for Automatic Speech Recognition (ASR) based on models trained with Kaldi.

LinTO-STT-Kaldi can either be used as a standalone transcription service or deployed within a micro-services infrastructure using a message broker connector.

It can be used to do offline or real-time transcriptions.

Pre-requisites

Hardware

To run the transcription models you'll need:

  • At least 7Go of disk space to build the docker image.
  • Up to 7GB of RAM depending on the model used.
  • One CPU per worker. Inference time scales on CPU performances.

Model

LinTO-STT-Kaldi accepts two kinds of models:

  • LinTO Acoustic and Languages models.
  • Vosk models.

We provide home-cured models (v2) on dl.linto.ai. Or you can also use Vosk models available here.

Docker

The transcription service requires docker up and running.

(micro-service) Service broker and shared folder

The STT only entry point in task mode are tasks posted on a message broker. Supported message broker are RabbitMQ, Redis, Amazon SQS. On addition, as to prevent large audio from transiting through the message broker, STT-Worker use a shared storage folder (SHARED_FOLDER).

Deploy LinTO-STT-Kaldi

1- First step is to build or pull the image:

git clone https://github.com/linto-ai/linto-stt.git
cd linto-stt
docker build . -f kaldi/Dockerfile -t linto-stt-kaldi:latest

or

docker pull lintoai/linto-stt-kaldi

2- Download the models

Have the acoustic and language model ready at AM_PATH and LM_PATH if you are using LinTO models. If you are using a Vosk model, have it ready at MODEL.

3- Fill the .env file

An example of .env file is provided in kaldi/.envdefault.

PARAMETER DESCRIPTION EXEMPLE
SERVICE_MODE STT serving mode see Serving mode http|task|websocket
MODEL_TYPE Type of STT model used. lin|vosk
ENABLE_STREAMING Using http serving mode, enable the /streaming websocket route true|false
SERVICE_NAME Using the task mode, set the queue's name for task processing my-stt
SERVICE_BROKER Using the task mode, URL of the message broker redis://my-broker:6379
BROKER_PASS Using the task mode, broker password my-password
STREAMING_PORT Using the websocket mode, the listening port for ingoing WS connexions. 80
CONCURRENCY Maximum number of parallel requests >1

Serving mode

Serving Modes

STT can be used three ways:

Mode is specified using the .env value or environment variable SERVING_MODE.

SERVICE_MODE=http

HTTP Server

The HTTP serving mode deploys a HTTP server and a swagger-ui to allow transcription request on a dedicated route.

The SERVICE_MODE value in the .env should be set to http.

docker run --rm \
-p HOST_SERVING_PORT:80 \
-v AM_PATH:/opt/AM \
-v LM_PATH:/opt/LM \
--env-file .env \
linto-stt-kaldi:latest

This will run a container providing an HTTP API binded on the host HOST_SERVING_PORT port.

Parameters:

Variables Description Example
HOST_SERVING_PORT Host serving port 80
AM_PATH Path to the acoustic model on the host machine mounted to /opt/AM /my/path/to/models/AM_fr-FR_v2.2.0
LM_PATH Path to the language model on the host machine mounted to /opt/LM /my/path/to/models/fr-FR_big-v2.2.0
MODEL_PATH Path to the model (using MODEL_TYPE=vosk) mounted to /opt/model /my/path/to/models/vosk-model

Celery task

The TASK serving mode connect a celery worker to a message broker.

The SERVICE_MODE value in the .env should be set to task.

You need a message broker up and running at MY_SERVICE_BROKER.

docker run --rm \
-v AM_PATH:/opt/AM \
-v LM_PATH:/opt/LM \
-v SHARED_AUDIO_FOLDER:/opt/audio \
--env-file .env \
linto-stt-kaldi:latest

Parameters:

Variables Description Example
AM_PATH Path to the acoustic model on the host machine mounted to /opt/AM /my/path/to/models/AM_fr-FR_v2.2.0
LM_PATH Path to the language model on the host machine mounted to /opt/LM /my/path/to/models/fr-FR_big-v2.2.0
MODEL_PATH Path to the model (using MODEL_TYPE=vosk) mounted to /opt/model /my/path/to/models/vosk-model
SHARED_AUDIO_FOLDER Shared audio folder mounted to /opt/audio /my/path/to/models/vosk-model

Websocket Server

Websocket server's mode deploy a streaming transcription service only.

The SERVICE_MODE value in the .env should be set to websocket.

Usage is the same as the http streaming API

Usages

HTTP API

/healthcheck

Returns the state of the API

Method: GET

Returns "1" if healthcheck passes.

/transcribe

Transcription API

  • Method: POST
  • Response content: text/plain or application/json
  • File: An Wave file 16b 16Khz

Return the transcripted text using "text/plain" or a json object when using "application/json" structure as followed:

{
  "text" : "This is the transcription",
  "words" : [
    {"word":"This", "start": 0.123, "end": 0.453, "conf": 0.9},
    ...
  ]
  "confidence-score": 0.879
}

/streaming

The /streaming route is accessible if the ENABLE_STREAMING environment variable is set to true.

The route accepts websocket connexions. Exchanges are structured as followed:

  1. Client send a json {"config": {"sample_rate":16000}}.
  2. Client send audio chunk (go to 3- ) or {"eof" : 1} (go to 5-).
  3. Server send either a partial result {"partial" : "this is a "} or a final result {"text": "this is a transcription"}.
  4. Back to 2-
  5. Server send a final result and close the connexion.

Connexion will be closed and the worker will be freed if no chunk are received for 10s.

/docs

The /docs route offers a OpenAPI/swagger interface.

Through the message broker

STT-Worker accepts requests with the following arguments: file_path: str, with_metadata: bool

  • file_path: Is the location of the file within the shared_folder. /.../SHARED_FOLDER/{file_path}
  • with_metadata: If True, words timestamps and confidence will be computed and returned. If false, the fields will be empty.

Return format

On a successfull transcription the returned object is a json object structured as follow:

{
    "text" : "this is the transcription as text",
    "words": [
        {
        "word" : "this",
        "start": 0.0,
        "end": 0.124,
        "conf": 1.0
        },
        ...
    ],
    "confidence-score": ""
}
  • The text field contains the raw transcription.
  • The word field contains each word with their time stamp and individual confidence. (Empty if with_metadata=False)
  • The confidence field contains the overall confidence for the transcription. (0.0 if with_metadata=False)

Tests

Curl

You can test you http API using curl:

curl -X POST "http://YOUR_SERVICE:YOUR_PORT/transcribe" -H  "accept: application/json" -H  "Content-Type: multipart/form-data" -F "file=@YOUR_FILE;type=audio/x-wav"

License

This project is developped under the AGPLv3 License (see LICENSE).

Acknowlegment.