在初始拒绝之后用 getUserMedia()提示获取权限

Use HTTPS. When the user gives permission once, it's remembered and Chrome does not ask for permission for that page again and you get access to the media immediately. This does not provide you a way to force the permission bar on the user again, but atleast makes sure you don't have to keep asking for it once the user grants the permission once.

If your app is running from SSL (https://), this permission will be persistent. That is, users won't have to grant/deny access every time.

See: http://www.html5rocks.com/en/tutorials/getusermedia/intro/

jeffreyveon's answer will help reduce the chance that your user will choose deny, since she will only have to choose once.

In case she does click deny, you can provide a message that explains why you need the permission and how to update her choice. For example:

navigator.getUserMedia (
// constraints
{
video: true,
audio: true
},


// successCallback
function(localMediaStream) {
var video = document.querySelector('video');
video.src = window.URL.createObjectURL(localMediaStream);
video.onloadedmetadata = function(e) {
// Do something with the video here.
};
},


// errorCallback
function(err) {
if(err === PERMISSION_DENIED) {
// Explain why you need permission and how to update the permission setting
}
}
);

Please be aware of below points.

1. Localhost: In Localhost Chrome Browser asking permission only one time and Firefox every pageload.

2. HTTPS: Both Browsers Chrome and Firefox asking permission only one time.

Chrome implements the Permissions API in navigator.permissions, and that applies to both camera and microphone permissions too.

So as of now, before calling getUserMedia(), you could use this API to query the permission state for your camera and microphone :

 navigator.permissions.query({name: 'microphone'})
.then((permissionObj) => {
console.log(permissionObj.state);
})
.catch((error) => {
console.log('Got error :', error);
})


navigator.permissions.query({name: 'camera'})
.then((permissionObj) => {
console.log(permissionObj.state);
})
.catch((error) => {
console.log('Got error :', error);
})

On success, permissionObj.state would return denied, granted or prompt.

Useful SF question/answer here

For a cross browser solution, one simple approach can be to monitor the time difference between when the getUserMedia() Promise is called, and when it is rejected or resolved, like so :

// In the Promise handlers, if Date.now() - now < 500 then we can assume this is a persisted user setting
var now = Date.now();
navigator.mediaDevices.getUserMedia({audio: true, video: false})
.then(function(stream) {
console.log('Got stream, time diff :', Date.now() - now);
})
.catch(function(err) {
console.log('GUM failed with error, time diff: ', Date.now() - now);
});

This Medium article gives more details.

Hope this helps!

The updated answer to this is that Chrome (currently testing on 73) no longer continuously prompts for camera access when the request is over HTTP.

Firefox however, does.

Ideally, you should be able to use the Permissions API before calling getUserMedia() to find out if the user has already granted or denied access to the camera and microphone, but this isn't yet available on Safari which accounts for a significant portion of users. Calling getUserMedia() will have an error in any one of the following cases:

• user clicks "Block" and does not allow camera/microphone access
• the browser itself does not have system permission to access the camera or microphone (common on macOS)
• another app like Zoom is using the video stream already (common on Windows)
• ...and more

You would want to prompt for permissions again in any of these cases after the user has resolved the issue.

Philippe Sultan's answer for using getUserMedia() is a great solution for prompting camera and microphone permissions across all browsers. Unforunately, the errors from getUserMedia() are wildly inconsistent across browsers and OS's. Chrome will have "NotReadableError" and "NotAllowedError" while Firefox is presenting a "NotFoundError" or "NotAllowedError". And Firefox is the only browser with any kind of error documentation.

You can use the mic-check package to request permissions for the camera and microphone. It will check the browser/OS to group all of the errors into more user-actionable error categories, like UserPermissionDenied, SystemPermissionDenied, and CouldNotStartVideoSource.

Install it with npm i mic-check or yarn add mic-check.

Use it with the code below:

import {
MediaPermissionsError
MediaPermissionsErrorType,
requestMediaPermissions
} from 'mic-check';


requestMediaPermissions()
.then(() => {
// can successfully access camera and microphone streams
// DO SOMETHING HERE
})
.catch((err: MediaPermissionsError) => {
const { type, name, message } = err;
if (type === MediaPermissionsErrorType.SystemPermissionDenied) {
// browser does not have permission to access camera or microphone
} else if (type === MediaPermissionsErrorType.UserPermissionDenied) {
// user didn't allow app to access camera or microphone
} else if (type === MediaPermissionsErrorType.CouldNotStartVideoSource) {
// camera is in use by another application (Zoom, Skype) or browser tab (Google Meet, Messenger Video)
// (mostly Windows specific problem)
} else {
// not all error types are handled by this library
}
});

Hope this helps! You can also learn more about the problem here.