<style>
        html,body{position:relative;height:100%;}
        .main { display: flex; flex-direction: row; justify-content:space-between;width:100%}
        #canvas{background-color:#eee;}
        .btnBox { display:flex;align-items:center;justify-content:center; position: absolute; bottom: 0px; left: 0px; width: 100%; height: 60px; background-color: #eee; border-top: solid 1px #ddd; }
        #btnSave{margin-left:20px;}
    </style>

<div class="main">
        <video id="video" autoplay style="width: 640px;height: 480px"></video>
        <!--拍照按钮-->
        <!--描绘video截图-->
        <canvas id="canvas" width="640" height="480"></canvas>

    </div>
    <div class="text-center btnBox">
        <button id="capture" class="btn btn-success"><i class="fa fa-camera"></i> 拍照</button>  
        <button id="btnSave" class="btn btn-success"><i class="fa fa-save"></i> 使用此图片</button>
    </div>

  
    <script>
        var qid =@ViewBag.qid;
        window.onload = function () {
            //访问用户媒体设备的兼容方法
            function getUserMedia(constraints, success, error) {
                if (navigator.mediaDevices.getUserMedia) {
                    //最新的标准API
                    navigator.mediaDevices.getUserMedia(constraints).then(success).catch(error);
                } else if (navigator.webkitGetUserMedia) {
                    //webkit核心浏览器
                    navigator.webkitGetUserMedia(constraints, success, error)
                } else if (navigator.mozGetUserMedia) {
                    //firfox浏览器
                    navigator.mozGetUserMedia(constraints, success, error);
                } else if (navigator.getUserMedia) {
                    //旧版API
                    navigator.getUserMedia(constraints, success, error);

                }
            }

            let video = document.getElementById('video');
            let canvas = document.getElementById('canvas');
            let context = canvas.getContext('2d');
            function success(stream) {
                //兼容webkit核心浏览器
                //let CompatibleURL = window.URL || window.webkitURL;
                //将视频流设置为video元素的源
                // console.log(stream);
                //video.src = CompatibleURL.createObjectURL(stream);
                video.srcObject = stream;
                video.play();
            }
            function error(error) {
                console.log(`访问用户媒体设备失败${error.name}, ${error.message}`);
            }

            if (navigator.mediaDevices.getUserMedia || navigator.getUserMedia || navigator.webkitGetUserMedia || navigator.mozGetUserMedia) {
                if (!navigator.mediaDevices || !navigator.mediaDevices.enumerateDevices) {
                    console.log("enumerateDevices() not supported.");
                    return;
                }
                // 列出摄像头和麦克风
                var exArray = [];
                navigator.mediaDevices.enumerateDevices()
                    .then(function (devices) {
                        devices.forEach(function (device) {
                            // console.log(device.kind + ": " + device.label +
                            // " id = " + device.deviceId);
                            if (device.kind == "videoinput") {
                                // alert(device.label);
                                exArray.push(device.deviceId);
                            }
                        });
                        var mediaOpts = { video: { width: 420, height: 120 } };
                        var mediaOpts =
                        {
                            video:
                            {
                                deviceId: { exact: exArray[1] }
                            }
                        };
                        //调用用户媒体设备, 访问摄像头
                        getUserMedia(mediaOpts, success, error);
                    })
                    .catch(function (err) {
                        console.log(err.name + ": " + err.message);
                    });

            } else {
                alert('不支持访问用户媒体');
            }
            var img = new Image();
            document.getElementById('capture').addEventListener('click', function () {
                context.drawImage(video, 0, 0, 640, 480);
               //var image_data = context.getImageData(0, 0, 480, 320);
                // var string = OCRAD(image_data.data);
                // string = _arrayBufferToBase64(image_data);
                var image = new Image();
                image.src = canvas.toDataURL("image/jpeg");
                console.log(image.src);
            
            })

        }

    </script>