aws-sdk-js-v3: Having problem with client-transcribe-streaming

Describe the bug By following the read me and build a test code. But I got the following error:

TypeError [ERR_INVALID_ARG_TYPE]: The "chunk" argument must be of type string or an instance of Buffer or Uint8Array. Received an instance of Object

I guess it something to do with the line:

yield { AudioEvent: { AudioChunk: chunk } };

Could anyone help check what’s wrong with my code?

SDK version number

    "@aws-sdk/client-transcribe-streaming": "^1.0.0-rc.8",
    "aws-sdk": "^2.808.0",

Is the issue in the browser/Node.js/ReactNative? Node.js

Details of the browser/Node.js/ReactNative version v15.4.0

To Reproduce (observed behavior)

const { TranscribeStreamingClient, StartStreamTranscriptionCommand } = require("@aws-sdk/client-transcribe-streaming");
const { PassThrough } = require("stream");
const { Readable } = require("stream");
var fs= require("fs");
var audioSource = fs.createReadStream("./speech.raw",{ highWaterMark: 512 });
var writeStream = fs.createWriteStream('./output.txt');
if(!audioSource){
    console.log("fail to open audioSource");
}
const client = new TranscribeStreamingClient();

const audioStream = async function* () {
  for await (const chunk of audioSource) {
     yield { AudioEvent: { AudioChunk: chunk } };
  }
};


const command = new StartStreamTranscriptionCommand({
  // The language code for the input audio. Valid values are en-GB, en-US, es-US, fr-CA, and fr-FR
  LanguageCode: "en-US",
  // The encoding used for the input audio. The only valid value is pcm.
  MediaEncoding: "pcm",
  // The sample rate of the input audio in Hertz. We suggest that you use 8000 Hz for low-quality audio and 16000 Hz for
  // high-quality audio. The sample rate must match the sample rate in the audio file.
  MediaSampleRateHertz: 16000,
  AudioStream: audioStream(),
});

async function go()
{
    try {
      const response = await client.send(command);
      //  await handleResponse(response);
      const transcriptsStream = Readable.from(response.TranscriptResultStream);
      transcriptsStream.pipe(writeStream);

    } catch (e) {
        console.log("e=%j",e);
      if (e.name === "InternalFailureException") {
        /* handle InternalFailureException */
      } else if (e.name === "ConflictException") {
        /* handle ConflictException */
      }
    } finally {
      /* clean resources like input stream */
    }
}

go();

Expected behavior Return the transcribe result.

Screenshots none

Additional context