问DOMException:无法启动Javascript网络摄像机录像机中的视频源

EN

Cannot access media devices:  DOMException: Could not start video source
(anonymous) @ scripts.js:43
Promise.catch (async)
(anonymous) @ scripts.js:42

<button id="btn-start-recording">Start Recording</button> <!-- OnClick it will run Javascript -->
<hr>
<video id="my-preview" controls autoplay></video>
<script src="./scripts.js"></script>
<script src="https://cdn.webrtc-experiment.com/RecordRTC.js"></script>
<script src="https://webrtc.github.io/adapter/adapter-latest.js"></script>

// When the user clicks on start video recording
    document.getElementById('btn-start-recording').addEventListener("click", function(){
        // Disable start recording button
        this.disabled = true;

        // Request access to the media devices
        navigator.mediaDevices.getUserMedia({
            audio: true, 
            video: true
        }).then(function(stream) {
            // Display a live preview on the video element of the page
            setSrcObject(stream, video);

            // Start to display the preview on the video element
            // and mute the video to disable the echo issue !
            video.play();
            video.muted = true;

            // Initialize the recorder
            recorder = new RecordRTCPromisesHandler(stream, {
                mimeType: 'video/webm',
                bitsPerSecond: 128000
            });

            // Start recording the video
            recorder.startRecording().then(function() {
                console.info('Recording video ...');
            }).catch(function(error) {
                console.error('Cannot start video recording: ', error);
            });

            // release stream on stopRecording
            recorder.stream = stream;

            // Enable stop recording button
            document.getElementById('btn-stop-recording').disabled = false;
        }).catch(function(error) {
            console.error("Cannot access media devices: ", error); // This is line 43.
        });
    }, false);