LexAudio

An example of using the Amazon Lex JavaScript SDK to send and receive audio from the Lex PostContent API. Demonstrates how to capture an audio device, record audio, convert the audio into a format that Lex will recognize, and play the response. All from a web browser.

A companion blog post to the example code can be found here.

Setup

1. Download and include the AWS JavaScript SDK:
   • http://aws.amazon.com/sdk-for-browser/
2. Download and include the Amazon Lex Audio SDK for JavaScript:
   • /dist/aws-lex-audio.min.js

    <script src="/js/aws-sdk.min.js"></script>
    <script src="/js/aws-lex-audio.min.js"></script>

Usage

Audio control

The Amazon Lex audioControl object provides a convenient API for acquiring a recording device, recording, exporting, and playing back audio.

Create the audio control

var audioControl = new LexAudio.audioControl();

Record audio

audioControl.startRecording();

Stop recording

audioControl.stopRecording();

Export and playback

audioControl.exportWAV(function(blob){
  audioControl.play(blob);
});

You can specify the export sample rate in Hz. 16000 Hz is the default if no value is provided. Note, the Amazon Lex Runtime API accepts 16kHz or 8kHz.

audioControl.exportWAV(function(blob){
  audioControl.play(blob);
}, 44100);

Conversation

The Amazon Lex conversation object provides an abstraction on top of the Amazon Lex Runtime PostContent API and makes it easy to manage conversation state (Passive, Listening, Recording, Speaking) and perform silence detection. It expects AWS.config.region and AWS.config.credentials to be set.

Set the AWS configuration region and credentials values

AWS.config.region = 'us-east-1';
AWS.config.credentials = ...;

Create the conversation object

var conversation = new LexAudio.conversation({lexConfig:{botName: 'BOT_NAME'}}, 
function (state) { // Called on each state change.
}, 
function (data) { // Called with the LexRuntime.PostContent response.
},
function (error){ // Called on error.
},
function (timeDomain) { // Called with audio time domain data (useful for rendering the recorded audio levels).
});

Start the conversation

conversation.advanceConversation();

Advances the conversation from Passive to Listening. By default, silence detection will be used to transition to Sending and the conversation will continue Listenting, Sending, and Speaking until the Dialog state is Fulfilled, ReadyForFulfillment, or Failed. Here are the conversation state transitions.

                                       onPlaybackComplete and ElicitIntent | ConfirmIntent | ElicitSlot
                                         +--------------------------------------------------------+
                                         |                                                        |
   +---------+                     +-----v-----+                     +---------+            +----------+
   |         | advanceConversation |           | advanceConversation |         | onResponse |          |
   | Passive +-------------------> | Listening +-------------------> | Sending +----------> | Speaking |
   |         |                     |           | onSilence           |         |            |          |
   +----^----+                     +-----------+                     +---------+            +----------+
        |                                                                                         |
        +-----------------------------------------------------------------------------------------+
           onPlaybackComplete and Fulfilled | ReadyForFulfillment | Failed | no silence detection

Setting silence detection to false allows you to manually transition out of the Passive and Listening states by calling conversation.advanceConversation().

var conversation = new LexAudio.conversation({silenceDetection: false, lexConfig:{botName: 'BOT_NAME'}}, ... );

You can pass silence detection configuration values to tune the silence detection algorithm. The time value is the amount of silence to wait for (in milliseconds). The amplitude is a threshold value (between 1 and -1). Above the amplitude threshold value is considered "noise". Below the amplitude threshold value is considered "silence". Here is the complete configuration object. Everything except botName has a default value.

{
  silenceDetection: true, 
  silenceDetectionConfig: {
    time: 1500,
    amplitude: 0.2
  },
  lexConfig:{
    botName: 'BOT_NAME',
    botAlias: '$LATEST',
    contentType: 'audio/x-l16; sample-rate=16000',
    userId: 'userId',
    accept: 'audio/mpeg'
  }
}

Browser support

This example code has been tested in the latest versions of:

• Chrome
• Firefox
• Safari (on macOS)