Amazon Transcribe streaming with Node.js using websocket

[ashishbutolajnu16]

I am working on a whatsapp chatbot where I receive audio file(ogg format) file url from Whatsapp and I get buffer and upload that file on S3(sample.ogg) Now what I want to use AWS Transcribe Streaming so I am creating readStream of file and sending to AWS transcribe I am using websocket but I am receiving Empty response of Sometimes when I Mhm mm mm response. Please can anyone tell what wrong I am doing in my code

const express = require('express')
const app = express()
const fs = require('fs');
const crypto = require('crypto'); // tot sign our pre-signed URL
const v4 = require('./aws-signature-v4'); // to generate our pre-signed URL
const marshaller = require("@aws-sdk/eventstream-marshaller"); // for converting binary event stream messages to and from JSON
const util_utf8_node = require("@aws-sdk/util-utf8-node");
var WebSocket = require('ws') //for opening a web socket
// our converter between binary event streams messages and JSON
const eventStreamMarshaller = new marshaller.EventStreamMarshaller(util_utf8_node.toUtf8, util_utf8_node.fromUtf8);

// our global variables for managing state
let languageCode;
let region = 'ap-south-1';
let sampleRate;
let inputSampleRate;
let transcription = "";
let socket;
let micStream;
let socketError = false;
let transcribeException = false;
// let languageCode = 'en-us'

app.listen(8081, (error, data) => {
if(!error) {
console.log(running at 8080----->>>>)
}
})

let handleEventStreamMessage = function (messageJson) {
let results = messageJson.Transcript.Results;

if (results.length > 0) {
    if (results[0].Alternatives.length > 0) {
        let transcript = results[0].Alternatives[0].Transcript;

        // fix encoding for accented characters
        transcript = decodeURIComponent(escape(transcript));

     console.log(`Transcpted is----->>${transcript}`)
    }
}

}

function downsampleBuffer (buffer, inputSampleRate = 44100, outputSampleRate = 16000){
if (outputSampleRate === inputSampleRate) {
return buffer;
}

var sampleRateRatio = inputSampleRate / outputSampleRate;
var newLength = Math.round(buffer.length / sampleRateRatio);
var result = new Float32Array(newLength);
var offsetResult = 0;
var offsetBuffer = 0;

while (offsetResult < result.length) {

    var nextOffsetBuffer = Math.round((offsetResult + 1) * sampleRateRatio);

    var accum = 0,
    count = 0;

    for (var i = offsetBuffer; i < nextOffsetBuffer && i < buffer.length; i++ ) {
        accum += buffer[i];
        count++;
    }

    result[offsetResult] = accum / count;
    offsetResult++;
    offsetBuffer = nextOffsetBuffer;

}

return result;

}

function pcmEncode(input) {
var offset = 0;
var buffer = new ArrayBuffer(input.length * 2);
var view = new DataView(buffer);
for (var i = 0; i < input.length; i++, offset += 2) {
var s = Math.max(-1, Math.min(1, input[i]));
view.setInt16(offset, s < 0 ? s * 0x8000 : s * 0x7FFF, true);
}
return buffer;
}

function getAudioEventMessage(buffer) {
// wrap the audio data in a JSON envelope
return {
headers: {
':message-type': {
type: 'string',
value: 'event'
},
':event-type': {
type: 'string',
value: 'AudioEvent'
}
},
body: buffer
};
}

function convertAudioToBinaryMessage(raw) {

if (raw == null)
    return;

// downsample and convert the raw audio bytes to PCM
let downsampledBuffer = downsampleBuffer(raw, inputSampleRate);
let pcmEncodedBuffer =  pcmEncode(downsampledBuffer);
setTimeout(function() {}, 1);
// add the right JSON headers and structure to the message
let audioEventMessage = getAudioEventMessage(Buffer.from(pcmEncodedBuffer));

//convert the JSON object + headers into a binary event stream message
let binary = eventStreamMarshaller.marshall(audioEventMessage);

return binary;

}

function createPresignedUrl() {
let endpoint = "transcribestreaming." + "us-east-1" + ".amazonaws.com:8443";

// get a preauthenticated URL that we can use to establish our WebSocket
return v4.createPresignedURL(
    'GET',
    endpoint,
    '/stream-transcription-websocket',
    'transcribe',
    crypto.createHash('sha256').update('', 'utf8').digest('hex'), {
        'key': <AWS_KEY>,
        'secret': <AWS_SECRET_KEY>,
        'protocol': 'wss',
        'expires': 15,
        'region': 'us-east-1',
        'query': "language-code=" + 'en-US' + "&media-encoding=pcm&sample-rate=" + 8000
    }
);

}

function showError(message) {
console.log("Error: ",message)
}

app.get('/convert', (req, res) => {
var file = 'recorded.mp3'
const eventStreamMarshaller = new marshaller.EventStreamMarshaller(util_utf8_node.toUtf8, util_utf8_node.fromUtf8);
let url = createPresignedUrl();
let socket = new WebSocket(url);
socket.binaryType = "arraybuffer";
let output = '';
const readStream = fs.createReadStream(file, { highWaterMark: 32 * 256 })
readStream.setEncoding('binary')
//let sampleRate = 0;
let inputSampleRate = 44100
readStream.on('end', function() {
console.log('finished reading----->>>>');
// write to file here.
// Send an empty frame so that Transcribe initiates a closure of the WebSocket after submitting all transcripts
let emptyMessage = getAudioEventMessage(Buffer.from(new Buffer([])));
let emptyBuffer = eventStreamMarshaller.marshall(emptyMessage);
socket.send(emptyBuffer);
})

// when we get audio data from the mic, send it to the WebSocket if possible
  socket.onopen = function() {
    readStream.on('data', function(chunk) {
     let binary = convertAudioToBinaryMessage(chunk);
     if (socket.readyState === socket.OPEN) {
         console.log(`sending to steaming API------->>>>`)
         socket.send(binary);
     }     
    });
        // the audio stream is raw audio bytes. Transcribe expects PCM with additional metadata, encoded as binary
    }
            // the audio stream is raw audio bytes. Transcribe expects PCM with additional metadata, encoded as binary


    socket.onerror = function () {
        socketError = true;
        showError('WebSocket connection error. Try again.');

    };

      // handle inbound messages from Amazon Transcribe
socket.onmessage = function (message) {
    //convert the binary event stream message to JSON
    let messageWrapper = eventStreamMarshaller.unmarshall(Buffer(message.data));
    //console.log(`messag -->>${JSON.stringify(messageWrapper)}`)
    let messageBody = JSON.parse(String.fromCharCode.apply(String, messageWrapper.body));
    console.log("results:.. ",JSON.stringify(messageBody))
    if (messageWrapper.headers[":message-type"].value === "event") {
        handleEventStreamMessage(messageBody);
    }
    else {
        transcribeException = true;
        showError(messageBody.Message);

}

}

let closeSocket = function () {
if (socket.OPEN) {

    // Send an empty frame so that Transcribe initiates a closure of the WebSocket after submitting all transcripts
    let emptyMessage = getAudioEventMessage(Buffer.from(new Buffer([])));
    let emptyBuffer = eventStreamMarshaller.marshall(emptyMessage);
    socket.send(emptyBuffer);
}

}

})