回答

不要在iframe内打开，必须在https或localhost下才能读取摄像头，代码如下：

<!DOCTYPE html>
<html lang="zh">
<head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />

</head>
<body>
    <video src=""></video>
    <script type="text/javascript">
        var opt = {
            audio: true,
            video: {
                width: 375,
                height:260
            }
        };
        navigator.mediaDevices.getUserMedia(opt)
        .then(function(mediaStream) {
            var video = document.querySelector('video');
            video.srcObject = mediaStream;
            video.onloadedmetadata = function(e) {
                video.play();
            };
        })
        .catch(function(err) {
            console.log(err.name + ": " + err.message);
        }); // always check for errors at the end.
    </script>
</body>
</html>