HTML userMedia facingMode："environment"不适用于 android phone

Question

它一直使用前置摄像头而不是后置摄像头这是我的代码：我添加了 facingMode: {exact:"environment"}，但它不起作用

const constraints = {
    video: true,
    facingMode: { exact: 'environment' }
};

if ('mediaDevices' in navigator && 'getUserMedia' in navigator.mediaDevices) {
    console.log("Let's get this party started")
}
navigator.mediaDevices.getUserMedia(constraints).
then((stream) => {video.srcObject = stream});
function displayImage()
{
    const selectedFile = document.getElementById('fileinput')
    //var image =document.getElementById('output')
    //image.src = URL.createObjectURL(selectedFile.files[0]);
    //selectedFile.files[0]
    const img = new Image()
    img.src = URL.createObjectURL(selectedFile.files[0])
    canvas.width = video.videoWidth
    canvas.height = video.videoHeight
    video.style.display="none"
    canvas.style.display ="inline"
    console.log(img)
    console.log("image uploaded")

    img.onload = function() {
        canvas.getContext('2d').drawImage(img, 0, 0,video.videoWidth,video.videoHeight);
        console.log('the image is drawn');
    }

}

Answer 1

facingMode 约束未完全实现，尤其是在移动设备中。

我发现 device 对象的 label 成员包含用于 environment-facing 相机的字符串 back 和用于 user-facing 相机在广泛的移动设备中，android 和 iOS。（有时这些字符串部分是大写的。）所以你可以这样做。与 facingMode 相比，它有点毛茸茸，但它确实有效。

/* get user's permission to muck around with video devices */
const tempStream = await navigator.mediaDevices.getUserMedia({video:true})
const devices = navigator.mediaDevices.enumerateDevices()
let frontDeviceId
let backDeviceId
if (devices.length > 0) {
  /* defaults so all this will work on a desktop */
  frontDeviceId = devices[0].deviceId;
  backDeviceId = devices[0].deviceId;
}
/* look for front and back devices */
devices.forEach (device => {
  if( device.kind === 'videoinput' ) {
    if( device.label && device.label.length > 0 ) {
      if( device.label.toLowerCase().indexOf( 'back' ) >= 0 ) 
        backDeviceId = device.deviceId
      else if( device.label.toLowerCase().indexOf( 'front' ) >= 0 )
        frontDeviceId = device.deviceId
    }
  }
}
/* close the temp stream */
const tracks = tempStream.getTracks()
if( tracks ) 
  for( let t = 0; t < tracks.length; t++ ) tracks[t].stop()
/* open the device you want */
const constraints = {
  video: true,
  deviceId: {exact: backDeviceId }
}
const stream = navigator.mediaDevices.getUserMedia(constraints)

Answer 2

您的约束设置不正确。

facingMode是video约束的成员，所以应该是

const constraints = {
  video: {
    facingMode: {
      exact: "environment"
    }
  }
};

Live Fiddle 来自带有后置摄像头的设备运行。

HTML userMedia facingMode："environment"不适用于 android phone

HTML userMedia facingMode: "environment"doesn't work on android phone

javascript

html

html5-video

getusermedia