How To Pass Different Audio Codecs To Symbl Endpoint

Sometimes you need to pass different audio codecs when passing the audio. This example shows how to pass them. The codecs currently supported are:

[OPUS](https://opus-codec.org/):
  - Supported Sample Rates -- 16000Hz, 24000Hz,48000Hz
  - Both CBR (Constant Bitrate) and VBR (Variable Bitrate) are supported
  - Support for in-band FEC

[SPEEX](https://www.speex.org/):
  - Supported Sample Rates -- 16000Hz
  - VBR is not supported

[LINEAR16](https://tools.ietf.org/html/rfc2586)
  - Supported Sample Rates -- 44100Hz

[MULAW](https://en.wikipedia.org/wiki/G.711#%CE%BC-law)
  - Supported Sample Rates -- 8000Hz

info

We recommend using OPUS as compared to other codecs because it provides the most flexibility in terms of audio transportation and also has packet retransmission mechanisms like FEC which work well, especially in low-bandwidth scenarios.

Throughout the documentation you'll find various references to these variable names, which you will have to replace with your values:

Key	Description
`APP_ID`	The application ID you get from the home page of the platform.
`APP_SECRET`	The application secret you get from the home page of the platform.
`AUTH_TOKEN`	The JWT you get after authentication with Sybml.
`DEFAULT_PHONE_NUMBER`	A phone number that you want the API to connect to. Be sure to include the country code.
`EMAIL_ADDRESS`	The email address you wish to send the summary email to.

View on Github

Getting started#

This example runs on node server, so we will use symbl-node package.

Open .env file and add your APP_ID, APP_SECRET, EMAIL_ADDRESS.

require('dotenv').config();
const {sdk} = require('symbl-node');

Initialize the SDK#

Let's start by initialising symbl-node sdk

await sdk.init({
  appId: process.env.APP_ID,
  appSecret: process.env.APP_SECRET,
  basePath: 'https://api.symbl.ai'
});

Connect to Endpoint#

Now after we initialized, we need to start the connection by running

const connection = await sdk.startEndpoint(endpointConfig);

Set Up Configuration Options#

So how do you pass custom codecs? It's as simple as passing custom audio config

endpoint: {
  //*****************Custom Audio Config******************
  audioConfig: {
    encoding: 'OPUS',
    sampleRate: 16000,
  },
  //******************************************************
  type: 'pstn',
  phoneNumber: process.env.DEFAULT_PHONE_NUMBER,
},

If you have a requirement to use a codec not included in the ones above or have any other queries, please drop an e-mail to support@symbl.ai.

info

If you have any questions or concerns about our API, you can join our Support Slack or send us an email at developer@symbl.ai

Full Code Example#

/*
 * This example shows how to pass in different Audio Codecs. The ones currently supported are
 *   OPUS:
 *     * Supported Sample Rates -- 16000Hz, 24000Hz, 48000Hz
 *     * Both CBR (Constant Bitrate) and VBR (Variable Bitrate) are supported
 *     * Support for in-band FEC
 *
 *   SPEEX:
 *     * Supported Sample Rates -- 16000Hz
 *     * VBR is not supported
 *
 *   LINEAR16:
 *     * Supported Sample Rates -- 44100Hz
 *
 *   MULAW:
 *     * Supported Sample Rates -- 8000Hz
 *
 *   NOTE: We recommend using OPUS as compared to other codecs because it provides the most flexibility in terms of
 *         audio transportation and also has packet retransmission mechanisms like FEC which work well especially
 *         in low-bandwidth scenarios.
 *
 *   If you have a requirement to use a codec not included in the ones above or have any other queries,
 *   please drop an e-mail to support@symbl.ai
 */
require('dotenv').config()
const {sdk, SpeakerEvent} = require('symbl-node')

const getScheduleEvent = (sdk, connectionId) => {
  return (eventType, user, time) => {
    setTimeout(() => {
      const speakerEvent = new SpeakerEvent({
        type: eventType,
        user,
      })
      speakerEvent.timestamp = new Date().toISOString()

      console.log(
        `Pushing event [${speakerEvent.timestamp}] ${speakerEvent.type} : ${speakerEvent.user.name}`,
      )

      sdk.pushEventOnConnection(connectionId, speakerEvent.toJSON(), (err) => {
        if (err) {
          console.error('Error during push event.', err)
        } else {
          console.log('Event pushed!')
        }
      })
    }, time * 1000)
  }
}

const users = {
  john: {
    userId: 'John@example.com',
    name: 'John',
  },
  mary: {
    userId: 'mary@example.com',
    name: 'Mary',
  },
  tim: {
    userId: 'tim@example.com',
    name: 'Tim',
  },
  jennifer: {
    userId: 'jennifer@example.com',
    name: 'Jennifer',
  },
}
;(async () => {
  try {
    // Initialize the SDK
    await sdk.init({
      appId: process.env.APP_ID,
      appSecret: process.env.APP_SECRET,
      basePath: 'https://api.symbl.ai',
    })

    const connection = await sdk.startEndpoint({
      endpoint: {
        //*****************Custom Audio Config******************
        audioConfig: {
          encoding: 'OPUS',
          sampleRate: 16000,
        },
        //******************************************************
        type: 'pstn',
        phoneNumber: process.env.DEFAULT_PHONE_NUMBER,
      },
      actions: [
        {
          invokeOn: 'stop',
          name: 'sendSummaryEmail',
          parameters: {
            emails: ['vladimir.novick@symbl.ai'],
          },
        },
      ],
      data: {
        session: {
          name: 'Ship-wide nanomachines, to the center.',
        },
      },
    })
    const connectionId = connection.connectionId
    console.log('Successfully connected.', connectionId)

    const scheduleEvent = getScheduleEvent(sdk, connectionId)

    setTimeout(() => {
      // This is just for interactive purpose was to show the elapsed time.

      scheduleEvent(SpeakerEvent.types.startedSpeaking, users.john, 0)
      scheduleEvent(SpeakerEvent.types.stoppedSpeaking, users.john, 4)

      scheduleEvent(SpeakerEvent.types.startedSpeaking, users.mary, 4)
      scheduleEvent(SpeakerEvent.types.stoppedSpeaking, users.mary, 9)

      // Scheduling stop endpoint call after 60 seconds
      setTimeout(() => {
        console.log('stopping connection ' + connection.connectionId)
        sdk
          .stopEndpoint({
            connectionId,
          })
          .then(() => {
            console.log('Stopped the connection')
          })
          .catch((err) =>
            console.error('Error while stopping the connection.', err),
          )
      }, 10000)
    }, 1000)
  } catch (err) {
    console.error('Error in SDK initialization.', err)
  }
})()

Running The Example#

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. Now in the terminal run

$ node app.js

If successful you should receive a response in the console.

info

If you have any questions or concerns about our API, you can join our Support Slack or send us an email at developer@symbl.ai