The duration read-only property of the EncodedAudioChunk interface returns an integer indicating the duration of the audio in microseconds.

An integer.

In the following example the duration is printed to the console.

const init = {
  type: "key",
  data: audioBuffer,
  timestamp: 23000000,
  duration: 2000000,
};
chunk = EncodedAudioChunk(init);

console.log(chunk.duration); //2000000