我有问题。

Question

// Older browsers might not implement mediaDevices at all, so we set an empty object first
if (navigator.mediaDevices === undefined) {
  navigator.mediaDevices = {};
}

// Some browsers partially implement mediaDevices. We can't just assign an object
// with getUserMedia as it would overwrite existing properties.
// Here, we will just add the getUserMedia property if it's missing.
if (navigator.mediaDevices.getUserMedia === undefined) {
  navigator.mediaDevices.getUserMedia = function(constraints) {

    // First get ahold of the legacy getUserMedia, if present
    var getUserMedia = navigator.webkitGetUserMedia || navigator.mozGetUserMedia;

    // Some browsers just don't implement it - return a rejected promise with an error
    // to keep a consistent interface
    if (!getUserMedia) {
      return Promise.reject(new Error('getUserMedia is not implemented in this browser'));
    }

    // Otherwise, wrap the call to the old navigator.getUserMedia with a Promise
    return new Promise(function(resolve, reject) {
      getUserMedia.call(navigator, constraints, resolve, reject);
    });
  }
}

navigator.mediaDevices.getUserMedia({
    audio: !true,
    video: true
  })
  .then(function(stream) {
    var video = document.querySelector('video');
    // Older browsers may not have srcObject
    if ("srcObject" in video) {
      video.srcObject = stream;
    } else {
      // Avoid using this in new browsers, as it is going away.
      video.src = window.URL.createObjectURL(stream);
    }
    video.onloadedmetadata = function(e) {
      video.play();
    };
  })
  .catch(function(err) {
    console.log(err.name + ": " + err.message);
  });

<video id="video" width="640" height="480" autoplay></video>
<button id="snap">Snap Photo</button>
<canvas id="canvas" width="640" height="480"></canvas>

注意，如果您不在边缘的安全上下文（https），则如下所示：

https：//developer.mozilla.org/en-en-us/docs/web/api/mediadiadevices /getusermedia

为了在所有现代浏览器中可靠地使用

navigator.MediaDevices

，您需要使用

undefined

Answer 1