HTML5通过navigator.mediaDevices.getUserMedia调用手机摄像头问题

文章主要介绍了HTML5通过navigator.mediaDevices.getUserMedia调用手机摄像头问题，本文通过实例代码给大家介绍的非常详细,需要的朋友可以参考下

navigator.mediaDevices.getUserMedia

应项目要求，需要实现移动端app嵌入H5页面完成实人认证的功能。打开getUserMedia文档，链接如下：
https://developer.mozilla.org/zh-CN/docs/Web/API/MediaDevices/getUserMedia
看上去很简单，最终却写的怀疑人生。

API环境

问题一：（为什么不管怎么配置都显示前置摄像头）

想正常使用API必须在https环境下进行，否则你会发现不管怎么写，都只能调用默认的摄像头（大部分都是前置，只有少部分是后置）
前端开发者可以将文件上传至"码云"仓库，获取https链接然后在手机上预览
链接：码云仓库入口

问题二：（API在安卓和iOS效果一样吗？）

根据官方文档，目前navigator.mediaDevices.getUserMedia在ios上只支持11版本以上，且只能在safari正常运行。安卓目前没有发现版本限制，需要兼容的代码如下

if (navigator.mediaDevices === undefined) {
    navigator.mediaDevices = {};
 }
if (navigator.mediaDevices.getUserMedia === undefined) {
    navigator.mediaDevices.getUserMedia = function (constraints) {
    var getUserMedia = navigator.getUserMedia || navigator.webkitGetUserMedia || navigator.mozGetUserMedia || navigator.msGetUserMedia || navigator.oGetUserMedia;
    if (!getUserMedia) {
        return Promise.reject(new Error('getUserMedia is not implemented in this browser'));
    }
    return new Promise(function (resolve, reject) {
        getUserMedia.call(navigator, constraints, resolve, reject);
    });
  }
}

问题三：（第一次启用成功调用前置摄像头，第二次需要调用后置却黑屏或者失败）

失败的原因很多，列举两个一开始我遇到的问题
1.前置摄像头调用后，摄像功能需要关闭后才能正常执行第二次调用，否则会报错：设备被占用。解决方法，在每次执行调用方法前，先关闭摄像设备。

if (window.stream) {
    window.stream.getTracks().forEach(track => {
          track.stop();
    });
}

亲测有用，别的找了很多停止的方法都没有效果。
2.调用后置API的方法还是无法唤醒后置摄像头，于是我找到另外一个方法，通过查看手机摄像头ID，来直接唤醒后置。

var deviceInfoId="", //摄像头ID
    num = 0, //摄像头数量
    carema = []; //摄像头ID数组
    //在页面加载完成后获得设备ID数组
window.onload = navigator.mediaDevices.enumerateDevices().then(gotDevices);
function gotDevices(deviceInfos) {
        for (let i = 0; i < deviceInfos.length; ++i) {
            if (deviceInfos[i].kind === 'videoinput') {
                carema.push(deviceInfos[i].deviceId)
              }
        }
        deviceInfoId = carema[后置位置];
}
            var constraints = {
                audio: false,
                video: {
                    deviceId: deviceInfoId,
                    //放在app里面需要下面配置一下
                    "permissions": {
                        "audio-capture": {
                            "description": "Required to capture audio using getUserMedia()"
                        },
                        "video-capture": {
                            "description": "Required to capture video using getUserMedia()"
                        }
                    }
                }
            };
            navigator.mediaDevices.getUserMedia(constraints)
                .then(function (stream) {
                    var video = document.getElementById('video');
                    try {
                        window.stream = stream;
                        video.srcObject = stream;
                    } catch (error) {
                        video.src = window.URL.createObjectURL(stream);
                    }
                    this.localMediaStream = stream;
                    // video.play();   这个加不加好像没有影响
                })
                .catch(function (err) {
                    console.log(err.name + ": " + err.message);
                });

如果只是一部手机可以这样，但是测试了多部手机发现摄像头数组毫无规律可循，这个方法慎用。
如果页面上添加选择摄像设备的按钮的话，这个方法还是不错的。查看设备能调用几个摄像头链接如下：https://webrtc.github.io/samples/src/content/devices/input-output/ 
由于我们的项目页面不希望出现切换按钮，面对后置出现的众多BUG，最终选择放弃，使用input调用摄像头。

成功调用后用canvas实现成像并适应屏幕大小

我这里的代码是取video的宽高然后复制给canvas，这样可以让canvas和video保持一致，只用给video设置宽度100%，高度调节成合适的值，就实现了适应手机屏幕。

var video = document.getElementById('video');
          var canvas = document.getElementById('canvas'),
              ctx = canvas.getContext('2d'),
              CHeight = video.clientHeight, //获取屏幕大小让canvas自适应
              CWidth = video.clientWidth;
          canvas.width = CWidth;
          canvas.height = CHeight;
          //localMediaStream 在data里定义一个{}
          if (localMediaStream) {
              ctx.drawImage(video, 0, 0, CWidth, CHeight);
              var dataURL = canvas.toDataURL('image/jpeg'); //dataURL = 'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAA'
              img.src = dataURL;

video成像镜像问题

API唤醒的前置摄像头是相反的，很不舒服很不舒服。
之后用css处理一下给video添加 transform: rotate(180deg),可以实现反转，但是还是没有达到和手机一样的效果。
这时候可以选择通过设备ID调用前置摄像头，前置摄像头的laval一直都是“default”，也有的是空值，但是也能实现。
配置代码如下：

var constraints = window.constraints = {
               audio: false,
               video: {
                   sourceId: 'default',
                   facingMode:  { exact: "user" } 
               }
             };

完美调用自己手机的前置摄像头！！！

完整代码如下：
页面代码：

<div @click='moveToCameraAVG()' v-cloak>
     <img v-if="imginfo!==''" :src="imginfo" />
     <div class="warm_title2">点击自拍一张头像</div>
</div>
<video id="video" class="pic_video" playsinline autoplay x5-video-player-type="h5" style='object-fit:fill'></video>
<canvas id="canvas" class="canvas_pic" style='margin: 0;padding: 0;'></canvas>
<div class="bottom_div">
    <div>拍照</div>
    <img src='images/pic_btn.png' class="capture-btn" @click='captureAvg' />
</div>

// 头像相机
       moveToCameraAVG() {
           var self = this;
           if (navigator.mediaDevices === undefined) {
               navigator.mediaDevices = {};
           }
           if (navigator.mediaDevices.getUserMedia === undefined) {
               navigator.mediaDevices.getUserMedia = function (constraints) {
                   var getUserMedia = navigator.getUserMedia || navigator.webkitGetUserMedia || navigator.mozGetUserMedia || navigator.msGetUserMedia || navigator.oGetUserMedia;
                   if (!getUserMedia) {
                       return Promise.reject(new Error('getUserMedia is not implemented in this browser'));
                   }
                   return new Promise(function (resolve, reject) {
                       getUserMedia.call(navigator, constraints, resolve, reject);
                   });
               }
           }
           if (window.stream) {
               window.stream.getTracks().forEach(track => {
                   track.stop();
               });
           }
           var constraints = window.constraints = {
               audio: false,
               video: {
                   sourceId: 'default',
                   facingMode:  { exact: "user" } 
               }
             };
           navigator.mediaDevices.getUserMedia(constraints)
               .then(function (stream) {
                   var video = document.getElementById('video');
                   try {
                       window.stream = stream;
                       video.srcObject = stream;
                   } catch (error) {
                       video.src = window.URL.createObjectURL(stream);
                   }
                   self.localMediaStream = stream;
                   video.play();
               })
               .catch(function (err) {
                   alert(err.name + ": " + err.message);
               });
       },
       //停止摄像机
       stopCapture: function () {
           var video = document.getElementById('video');
           if (!video.srcObject) return
           let stream = video.srcObject
           let tracks = stream.getTracks();
           tracks.forEach(track => {
               track.stop()
           })
       },
       // 头像照片
       captureAvg() {
           var vm = this;
           var video = document.getElementById('video');
           var canvas = document.getElementById('canvas'),
               ctx = canvas.getContext('2d'),
               CHeight = video.clientHeight, //获取屏幕大小让canvas自适应
               CWidth = video.clientWidth;
           canvas.width = CWidth;
           canvas.height = CHeight;
           if (vm.localMediaStream) {
               ctx.drawImage(video, 0, 0, CWidth, CHeight);
               var dataURL = canvas.toDataURL('image/jpeg'); //dataURL = 'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAA'
               vm.imginfo = dataURL;
               // 停止摄像机
               video.pause();
               this.stopCapture();
           }
       },

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