Receive live captions

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This example goes over how you can use the Symbl Streaming API to do live captioning. This example uses both the JavaScript SDK, which is meant to be run using Node.js, and native JavaScript which can be run in the browser:

Connect

The first thing we do is connect to the Web Socket using the SDK. If you're using the SDK you can use the onMessageResponse and onSpeechDetected handlers after the connection is established, otherwise you'll have to parse the response in the onmessage callback for the WebSocket.

Node.js

const {sdk} = require('symbl-node');
const uuid = require('uuid').v4;

(async () => {
  try {
    // Initialize the SDK. You can find the appId and appSecret at https://platform.symbl.ai.
    await sdk.init({
      appId: appId,
      appSecret: appSecret,
      basePath: 'https://api.symbl.ai',
    })

    // Need unique Id
    const id = uuid()

    // Start Realtime Request (Uses Real-time WebSocket API behind the scenes)
    const connection = await sdk.startRealtimeRequest({
      id,
      insightTypes: ['action_item', 'question'],
      config: {
        meetingTitle: 'My Test Meeting',
        confidenceThreshold: 0.7,
        timezoneOffset: 480, // Offset in minutes from UTC
        languageCode: 'en-US',
        sampleRateHertz: 44100,
      },
      speaker: {
        // Optional, if not specified, will simply not send an email in the end.
        userId: 'emailAddress', // Update with valid email
        name: 'My name'
      },
      handlers: {
        /**
         * This will return live speech-to-text transcription of the call.
         */
        onSpeechDetected: (data) => {
          console.log(JSON.stringify(data))
          if (data) {
            const {punctuated} = data
            console.log('Live: ', punctuated && punctuated.transcript)
          }
        },
        /**
         * When processed messages are available, this callback will be called.
         */
        onMessageResponse: (data) => {
          console.log('onMessageResponse', JSON.stringify(data, null, 2))
        },
      }
    });
  } catch (e) {
    console.error(e);
  }
})();

Connect Mic

After you connect, you want to connect to your device's microphone. This code is inserted after the connection and before the closing of the try...catch

const micInputStream = micInstance.getAudioStream()
/** Raw audio stream */
micInputStream.on('data', (data) => {
  // Push audio from Microphone to websocket connection
  connection.sendAudio(data)
})

micInputStream.on('error', function (err) {
  console.log('Error in Input Stream: ' + err)
})

micInputStream.on('startComplete', function () {
  console.log('Started listening to Microphone.')
})

micInputStream.on('silence', function () {
  console.log('Got SIGNAL silence')
})

micInstance.start()

setTimeout(async () => {
  // Stop listening to microphone
  micInstance.stop()
  console.log('Stopped listening to Microphone.')
  try {
    // Stop connection
    await connection.stop()
    console.log('Connection Stopped.')
  } catch (e) {
    console.error('Error while stopping the connection.', e)
  }
}, 60 * 1000) // Stop connection after 1 minute i.e. 60 secs

Testing

Create a javascript file named app.js and copy this code into the file. Fill in the placeholder values with the proper values. Use npm to install the required libraries: npm install symbl-node uuid. Now in the terminal run

$ node app.js

If successful you should receive a response in the console.

Native JavaScript

const accessToken = accessToken;
// Refer to the Authentication section for how to generate the accessToken: https://docs.symbl.ai/docs/developer-tools/authentication
const uniqueMeetingId = btoa("[email protected]"); // btoa will take a string and generate a unique ID
const symblEndpoint = `wss://api.symbl.ai/v1/streaming/${uniqueMeetingId}?access_token=${accessToken}`;

const ws = new WebSocket(symblEndpoint);

ws.onmessage = (event) => {
  // You can find the conversationId in event.message.data.conversationId;
  const data = JSON.parse(event.data);
  if (data.type === 'message' && data.message.hasOwnProperty('data')) {
    console.log('conversationId', data.message.data.conversationId);
  }
  if (data.type === 'message_response') {
    for (let message of data.messages) {
      console.log('message:', message.payload.content)
    }
  }
  console.log('event', event);
  console.log('Parsed Object', JSON.stringify(data, null, 2));
};

// Fired when the WebSocket closes unexpectedly due to an error or lost connetion
ws.onerror  = (err) => {
  console.error(err);
};

// Fired when the WebSocket connection has been closed
ws.onclose = (event) => {
  console.info('Connection to websocket closed');
};

// Fired when the connection succeeds.
ws.onopen = (event) => {
  ws.send(JSON.stringify({
    type: 'start_request',
    meetingTitle: 'Websockets How-to', // Conversation name
    insightTypes: ['question', 'action_item'], // Will enable insight generation
    config: {
      confidenceThreshold: 0.5,
      languageCode: 'en-US',
      speechRecognition: {
        encoding: 'LINEAR16',
        sampleRateHertz: 44100,
      }
    },
    speaker: {
      userId: '[email protected]',
      name: 'Example Sample',
    }
  }));
};

📘

Backward Compatibility

The previous endpoint wss://api.symbl.ai/v1/realtime/insights/ is now updated to wss://api.symbl.ai/v1/streaming/ to standardize our API nomenclature. This change is backward compatible. However, we recommend you to use the new endpoint.

Connect Mic

After you connect, you want to connect to your device's microphone. This code is inserted after the ws.onopen function:

const stream = await navigator.mediaDevices.getUserMedia({ audio: true, video: false });

/**
 * The callback function which fires after a user gives the browser permission to use
 * the computer's microphone. Starts a recording session which sends the audio stream to
 * the WebSocket endpoint for processing.
 */
const handleSuccess = (stream) => {
  const AudioContext = window.AudioContext;
  const context = new AudioContext();
  const source = context.createMediaStreamSource(stream);
  const processor = context.createScriptProcessor(1024, 1, 1);
  const gainNode = context.createGain();
  source.connect(gainNode);
  gainNode.connect(processor);
  processor.connect(context.destination);
  processor.onaudioprocess = (e) => {
    // convert to 16-bit payload
    const inputData = e.inputBuffer.getChannelData(0) || new Float32Array(this.bufferSize);
    const targetBuffer = new Int16Array(inputData.length);
    for (let index = inputData.length; index > 0; index--) {
        targetBuffer[index] = 32767 * Math.min(1, inputData[index]);
    }
    // Send audio stream to websocket.
    if (ws.readyState === WebSocket.OPEN) {
      ws.send(targetBuffer.buffer);
    }
  };
};


handleSuccess(stream);

Testing

Open up your browser's development environment and copy this code into the console. Replace the placeholder values with the proper values.

If successful you should receive a response in the console.

Handlers Reference

  • handlers: This object has the callback functions for different events

    • onSpeechDetected: To retrieve the real-time transcription results as soon as they are detected. You can use this callback to render live transcription which is specific to the speaker of this audio stream.

    onSpeechDetected JSON Response Example

    {
      "type": "recognition_result",
      "isFinal": true,
      "payload": {
        "raw": {
          "alternatives": [{
            "words": [{
              "word": "Hello",
              "startTime": {
                "seconds": "3",
                "nanos": "800000000"
              },
              "endTime": {
                "seconds": "4",
                "nanos": "200000000"
              }
            }, {
              "word": "world.",
              "startTime": {
                "seconds": "4",
                "nanos": "200000000"
              },
              "endTime": {
                "seconds": "4",
                "nanos": "800000000"
              }
            }],
            "transcript": "Hello world.",
            "confidence": 0.9128385782241821
          }]
        }
      },
      "punctuated": {
        "transcript": "Hello world."
      },
      "user": {
        "userId": "emailAddress",
        "name": "John Doe",
        "id": "23681108-355b-4fc3-9d94-ed47dd39fa56"
      }
    }
    

    • onMessageResponse: This callback function contains the "finalized" transcription data for this speaker and if used with multiple streams with other speakers this callback would also provide their messages.
      The "finalized" messages mean that the automatic speech recognition has finalized the state of this part of transcription and has declared it "final". Therefore, this transcription will be more accurate than onSpeechDetected.

    onMessageResponse JSON Response Example

    [{
      "from": {
        "id": "0a7a36b1-047d-4d8c-8958-910317ed9edc",
        "name": "John Doe",
        "userId": "emailAddress"
      },
      "payload": {
        "content": "Hello world.",
        "contentType": "text/plain"
      },
      "id": "59c224c2-54c5-4762-9582-961bf250b478",
      "channel": {
        "id": "realtime-api"
      },
      "metadata": {
        "disablePunctuation": true,
        "timezoneOffset": 480,
        "originalContent": "Hello world.",
        "words": "[{\"word\":\"Hello\",\"startTime\":\"2021-02-04T20:34:59.029Z\",\"endTime\":\"2021-02-04T20:34:59.429Z\"},{\"word\":\"world.\",\"startTime\":\"2021-02-04T20:34:59.429Z\",\"endTime\":\"2021-02-04T20:35:00.029Z\"}]",
        "originalMessageId": "59c224c2-54c5-4762-9582-961bf250b478"
      },
      "dismissed": false,
      "duration": {
        "startTime": "2021-02-04T20:34:59.029Z",
        "endTime": "2021-02-04T20:35:00.029Z"
      }
    }]
    

See Also