When I try to stream my webcam video by using getUserMedia() api a black screen is appearing

I am trying to access the user's webcam by using navigator.getUserMedia(). I am assigning the video.srcObject to this stream. But I am getting a black screen on video. I event tried with navigator.mediaDevices.getUserMedia()

<video controls id="webcam"></video>
<script>
    const webcam = document.getElementById("webcam"); 
    function startVideo() {
        navigator
            .getUserMedia({
                    video: true,
                    audio: false
                },
                liveStream => {
                    console.log(liveStream);
                    webcam.setAttribute("controls", 'true');
                    webcam.srcObject = liveStream;
                    webcam.play();
                },
                error => console.log(error)
            )
    }
    startVideo();
</script>