哪个相机将在移动设备中打开getUserMedia API?前部或后部

Question

使用getUserMedia API访问桌面上的摄像头时，会打开网络摄像头。当然，这有助于视频通信。但在移动设备中使用时会调用哪个摄像头。前凸轮或后凸轮？。选择相机需要代码吗？

Answer 1

有一个解决方案，用户可以选择其中一个摄像头。

使用HTML5 启用后置摄像头

通过从以下代码中评估sourceInfo.facing，您可以选择一个相机（"用户"或"环境"）（适用于当前chrome>=30）：https://simpl.info/getusermedia/sources/

'use strict';
var videoElement = document.querySelector('video');
var audioSelect = document.querySelector('select#audioSource');
var videoSelect = document.querySelector('select#videoSource');
navigator.getUserMedia = navigator.getUserMedia ||
  navigator.webkitGetUserMedia || navigator.mozGetUserMedia;
function gotSources(sourceInfos) {
  for (var i = 0; i !== sourceInfos.length; ++i) {
    var sourceInfo = sourceInfos[i];
    var option = document.createElement('option');
    option.value = sourceInfo.id;
    if (sourceInfo.kind === 'audio') {
      option.text = sourceInfo.label || 'microphone ' + (audioSelect.length + 1);
      audioSelect.appendChild(option);
    } else if (sourceInfo.kind === 'video') {
      option.text = sourceInfo.label || 'camera ' + (videoSelect.length + 1);
      videoSelect.appendChild(option);
    } else {
      console.log('Some other kind of source: ', sourceInfo);
    }
  }
}
if (typeof MediaStreamTrack === 'undefined'){
  alert('This browser does not support MediaStreamTrack.nnTry Chrome Canary.');
} else {
  MediaStreamTrack.getSources(gotSources);
}

function successCallback(stream) {
  window.stream = stream; // make stream available to console
  videoElement.src = window.URL.createObjectURL(stream);
  videoElement.play();
}
function errorCallback(error){
  console.log('navigator.getUserMedia error: ', error);
}
function start(){
  if (!!window.stream) {
    videoElement.src = null;
    window.stream.stop();
  }
  var audioSource = audioSelect.value;
  var videoSource = videoSelect.value;
  var constraints = {
    audio: {
      optional: [{sourceId: audioSource}]
    },
    video: {
      optional: [{sourceId: videoSource}]
    }
  };
  navigator.getUserMedia(constraints, successCallback, errorCallback);
}
audioSelect.onchange = start;
videoSelect.onchange = start;
start();

Answer 2

不幸的是，您（还？）无法通过代码选择它。

• Mozilla Firefox测试版：当用户接受共享相机时，他/她还可以选择要共享的相机。

• Chrome测试版：我只能使用面部摄像头。可能是可配置，但我不知道如何…

编辑：在chrome中，可以通过编程方式选择背面摄像头。请参阅本线程中Probot的下一个答案。

Answer 3

答案是肯定的，对于Android，默认的摄像头是前置摄像头（<=>用户）。因此，我开发了下面的脚本，以便在前置摄像头和后置摄像头之间进行选择

    //----------------------------------------------------------------------
    //  Here we list all media devices, in order to choose between
    //  the front camera and the rear camera.
    //      videoDevices[0] : Front Camera
    //      videoDevices[1] : Back Camera
    //  I used an array to save the devices ID 
    //  which I get with using devices.forEach()
    //  Then I set the video resolution.
    //----------------------------------------------------------------------
    navigator.mediaDevices.enumerateDevices()
    .then(devices => {
      var videoDevices = [0,0];
      var videoDeviceIndex = 0;
      devices.forEach(function(device) {
        console.log(device.kind + ": " + device.label +
          " id = " + device.deviceId);
        if (device.kind == "videoinput") {  
          videoDevices[videoDeviceIndex++] =  device.deviceId;    
        }
      });
      var constraints =  {width: { min: 1024, ideal: 1280, max: 1920 },
      height: { min: 776, ideal: 720, max: 1080 },
      deviceId: { exact: videoDevices[1]  } 
    };
    return navigator.mediaDevices.getUserMedia({ video: constraints });
  })
    .then(stream => {
      if (window.webkitURL) {
        video.src = window.webkitURL.createObjectURL(stream);
        localMediaStream = stream;
      } else if (video.mozSrcObject !== undefined) {
        video.mozSrcObject = stream;
      } else if (video.srcObject !== undefined) {
        video.srcObject = stream;
      } else {
        video.src = stream;
      }})
    .catch(e => console.error(e));