how to detect if getUserMedia with video and audio constraints has audio or not?

i want to detect, is there any audio or not while showing media stream in video tag in JavaScript. what i have done to show webcam stream to video tag is below, now i want to detect whether user speaks anything? how can i detect that? can anyone help me to solve this?

var constraints = { audio: { echoCancellation: true }, video: { width: 640, height: 480 } };
navigator.mediaDevices
            .getUserMedia(constraints)
            .then(function (mediaStream) {
                videoInput = document.querySelector("video");

                videoInput.srcObject = mediaStream;
                videoInput.onloadedmetadata = function (e) {
                    videoInput.play();
                };
            })
            .catch(function (err) {
                console.log(err.name + ": " + err.message);
            });