MediaDevices.getUserMedia()

The MediaDevices.getUserMedia() method prompts the user for permission to use one video and/or one audio input device such as a camera or screensharing and/or a microphone. If the user provides permission, then the returned Promise is resolved with the resulting MediaStream object. If the user denies permission, or media is not available, then the promise is rejected with PermissionDeniedError or NotFoundError respectively. Note that it is possible for the returned promise to neither resolve nor reject, as the user is not required to make a choice.

Syntax

navigator.mediaDevices.getUserMedia(constraints)
.then(function(mediaStream) { ... })
.catch(function(error) { ... })

Returns

A Promise that resolves to a MediaStream object.

Parameters

constraints

Is a MediaStreamConstraints object specifying the types of media to request, along with any requirements for each type.

The constraints parameter is a MediaStreamConstaints object with two members: video and audio, describing the media types requested. Either or both must be specified. If the browser cannot find all media tracks with the specified types that meet the constraints given, then the returned promise is rejected with NotFoundError.

The following requests both audio and video without any specific requirements:

{ audio: true, video: true }

While information about a user's cameras and microphones are inaccessible for privacy reasons, an application can request the camera and microphone capabilities it needs and wants, using additional constraints. The following expresses a preference for 1280x720 camera resolution:

{
  audio: true,
  video: { width: 1280, height: 720 }
}

The browser will try to honor this, but may return other resolutions if an exact match is not available, or the user overrides it.

To require a capability, use the keywords min, max, or exact (a.k.a. min == max). The following demands a minimum resolution of 1280x720:

{
  audio: true,
  video: {
    width: { min: 1280 },
    height: { min: 720 }
  }
}

If no camera exists with this resolution or higher, then the returned promise will be rejected with NotFoundError, and the user will not be prompted.

The reason for the difference in behavior is that the keywords min, max, and exact are inherently mandatory, whereas plain values and a keyword called ideal are not. Here's a fuller example:

{
  audio: true,
  video: {
    width: { min: 1024, ideal: 1280, max: 1920 },
    height: { min: 776, ideal: 720, max: 1080 }
  }
}

An ideal value, when used, has gravity, which means that the browser will try to find the setting (and camera, if you have more than one), with the smallest fitness distance from the ideal values given.

Plain values are inherently ideal, which means that the first of our resolution examples above could have been written like this:

{
  audio: true,
  video: {
    width: { ideal: 1280 },
    height: { ideal: 720 }
  }
}

Not all constraints are numbers. For example, on mobile devices, the following will prefer the front camera (if one is available) over the rear one:

{ audio: true, video: { facingMode: "user" } }

To require the rear camera, use:

{ audio: true, video: { facingMode: { exact: "environment" } } }

Errors

Rejections of the returned promise are made with a MediaStreamError object that is modeled on DOMException. Relevant errors are:

SecurityError

Permission to use a media device was denied by the user or the system.

NotFoundError

No media tracks of the type specified were found that satisfy the constraints specified.

Examples

Using the Promise

This example assigns the returned MediaStream object to the appropriate element.

var p = navigator.mediaDevices.getUserMedia({ audio: true, video: true });

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

p.catch(function(err) { console.log(err.name); }); // always check for errors at the end.

Width and height

Here's an example of using mediaDevices.getUserMedia(), including a polyfill to cope with older browsers.

var promisifiedOldGUM = function(constraints, successCallback, errorCallback) {

  // First get ahold of getUserMedia, if present
  var getUserMedia = (navigator.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(successCallback, errorCallback) {
    getUserMedia.call(navigator, constraints, successCallback, errorCallback);
  });
		
}

// 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 = promisifiedOldGUM;
}

// Prefer camera resolution nearest to 1280x720.
var constraints = { audio: true, video: { width: 1280, height: 720 } };

navigator.mediaDevices.getUserMedia(constraints)
.then(function(stream) {
  var video = document.querySelector('video');
  video.src = window.URL.createObjectURL(stream);
  video.onloadedmetadata = function(e) {
    video.play();
  };
})
.catch(function(err) {
  console.log(err.name + ": " + err.message);
});

Frame rate

Lower frame-rates may be desirable in some cases, like WebRTC transmissions with bandwidth restrictions.

var constraints = { video: { frameRate: { ideal: 10, max: 15 } } };

Front and back camera

On mobile phones.

var front = false;
document.getElementById('flip-button').onclick = function() { front = !front; };

var constraints = { video: { facingMode: (front? "user" : "environment") } };

Permissions

To use getUserMedia() in an installable app (for example, a Firefox OS app), you need to specify one or both of the following fields inside your manifest file:

"permissions": {
  "audio-capture": {
    "description": "Required to capture audio using getUserMedia()"
  },
  "video-capture": {
    "description": "Required to capture video using getUserMedia()"
  }
}

See permission: audio-capture and permission: video-capture for more information.

Specifications

Browser compatibility

[1] Older versions of Chrome and Opera implement navigator.webkitGetUserMedia, the prefixed version of the legacy navigator.getUserMedia method.

In Chrome, this promise-based interface is only available through the adapter.js polyfill, or using the flag chrome://flags/#enable-experimental-web-platform-features.

Chrome uses an outdated constraint syntax, but the syntax described here is available through the adapter.js polyfill.

[2] Older versions of Firefox implement navigator.mozGetUserMedia, the prefixed version of the legacy navigator.getUserMedia method.

This promise-based interface and the constraint syntax described here is available as of Firefox 38. Earlier versions (32-37) used an outdated constraint syntax, but the syntax described here, as well as the promise-based interface, is available there through the adapter.js polyfill.

Opera uses an outdated constraint syntax, but the syntax described here is available through the adapter.js polyfill.

[3] Chrome throws error if the page serving the script is loaded from insecure origin (i.e. HTTP).

See also

• The older navigator.getUserMedia legacy API.
• navigator.enumerateDevices - learn the types and number of devices the user has available.
• WebRTC - the introductory page to the API
• MediaStream API - the API for the media stream objects
• Taking webcam photos - a tutorial on using getUserMedia() for taking photos rather than video.