MediaDevices: getUserMedia() method

constraints

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

The constraints parameter is an 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 DOMException.

For both video and audio, its value is either a boolean or an object. The default value is false.

• If true is specified for a media type, the resulting stream is required to have that type of track in it. If one cannot be included for any reason, the returned promise will reject.
• If false is specified for a media type, the resulting stream must not have that type of track, or the returned promise will reject. Because both video and audio default to false, if the constraints object contains neither property or if it's not present at all, the returned promise will always reject.
• If an object is specified for a media type, the object is read as a MediaTrackConstraints dictionary.

A Promise whose fulfillment handler receives a MediaStream object when the requested media has successfully been obtained.

AbortError DOMException

Although the user and operating system both granted access to the hardware device, and no hardware issues occurred that would cause a NotReadableError DOMException, throw if some problem occurred which prevented the device from being used.

InvalidStateError DOMException

Thrown if current document is not fully active.

NotAllowedError DOMException

Thrown if one or more of the requested source devices cannot be used at this time. This will happen if the browsing context is insecure (that is, the page was loaded using HTTP rather than HTTPS). It also happens if the user has specified that the current browsing instance is not permitted access to the device, the user has denied access for the current session, or the user has denied all access to user media devices globally. On browsers that support managing media permissions with Permissions Policy, this error is returned if Permissions Policy is not configured to allow access to the input source(s).

Note: Older versions of the specification used SecurityError for this instead; SecurityError has taken on a new meaning.

NotFoundError DOMException

Thrown if no media tracks of the type specified were found that satisfy the given constraints.

NotReadableError DOMException

Thrown if, although the user granted permission to use the matching devices, a hardware error occurred at the operating system, browser, or Web page level which prevented access to the device.

OverconstrainedError DOMException

Thrown if the specified constraints resulted in no candidate devices which met the criteria requested. The error is an object of type OverconstrainedError, and has a constraint property whose string value is the name of a constraint which was impossible to meet, and a message property containing a human-readable string explaining the problem.

Note: Because this error can occur even when the user has not yet granted permission to use the underlying device, it can potentially be used as a fingerprinting surface.

SecurityError DOMException

Thrown if user media support is disabled on the Document on which getUserMedia() was called. The mechanism by which user media support is enabled and disabled is left up to the individual user agent.

TypeError

Thrown if the list of constraints specified is empty, or has all constraints set to false. This can also happen if you try to call getUserMedia() in an insecure context, since navigator.mediaDevices is undefined in an insecure context.

As an API that may involve significant privacy concerns, getUserMedia()'s specification lays out a wide array of privacy and security requirements that browsers are obligated to meet.

getUserMedia() is a powerful feature that can only be used in secure contexts; in insecure contexts, navigator.mediaDevices is undefined, preventing access to getUserMedia(). A secure context is, in short, a page loaded using HTTPS or the file:/// URL scheme, or a page loaded from localhost.

In addition, user permission is always required to access the user's audio and video inputs. Only a window's top-level document context for a valid origin can even request permission to use getUserMedia(), unless the top-level context expressly grants permission for a given <iframe> to do so using Permissions Policy. Otherwise, the user will never even be asked for permission to use the input devices.

For additional details on these requirements and rules, how they are reflected in the context in which your code is running, and about how browsers manage user privacy and security issues, read on.

As an API that may involve significant privacy concerns, getUserMedia() is held by the specification to very specific requirements for user notification and permission management. First, getUserMedia() must always get user permission before opening any media gathering input such as a webcam or microphone. Browsers may offer a once-per-domain permission feature, but they must ask at least the first time, and the user must specifically grant ongoing permission if they choose to do so.

Of equal importance are the rules around notification. Browsers are required to display an indicator that shows that a camera or microphone is in use, above and beyond any hardware indicator that may exist. They must also show an indicator that permission has been granted to use a device for input, even if the device is not actively recording at the moment.

For example in Firefox, the URL bar displays a pulsing red icon to indicate that recording is underway. The icon is gray if the permission is in place but recording is not currently underway. The device's physical light is used to indicate whether or not recording is currently active. If you've muted your camera (so-called "facemuting"), your camera's activity light goes out to indicate that the camera is not actively recording you, without discarding the permission to resume using the camera once muting is over.

There are a number of ways security management and controls in a user agent can cause getUserMedia() to return a security-related error.

Permissions Policy

The two Permissions Policy directives that apply to getUserMedia() are camera and microphone.

For example, this HTTP header will enable use of a camera by the document and any embedded <iframe> elements that are loaded from the same origin:

Permissions-Policy: camera=(self)

This will request access to the microphone for the current origin and the specific origin https://developer.mozilla.org:

Permissions-Policy: microphone=(self "https://developer.mozilla.org")

If you're using getUserMedia() within an <iframe>, you can request permission just for that frame, which is clearly more secure than requesting a more general permission. Here, indicate we need the ability to use both camera and microphone:

<iframe src="https://mycode.example.net/etc" allow="camera; microphone">
</iframe>

Encryption based security

The getUserMedia() method is only available in secure contexts. A secure context is one the browser is reasonably confident contains a document which was loaded securely, using HTTPS/TLS, and has limited exposure to insecure contexts. If a document isn't loaded in a secure context, the navigator.mediaDevices property is undefined, making access to getUserMedia() impossible.

Attempting to access getUserMedia() in this situation will result in a TypeError.

Document source security

Because of the obvious security concern associated with getUserMedia() if used unexpectedly or without security being carefully managed, it can only be used in secure contexts. There are a number of insecure ways to load a document that might, in turn, attempt to call getUserMedia(). The following are examples of situations in which getUserMedia() is not permitted to be called:

• A document loaded into a sandboxed <iframe> element cannot call getUserMedia() unless the <iframe> has its sandbox attribute set to allow-same-origin.
• A document loaded using a data:// or blob:// URL which has no origin (such as when one of these URLs is typed by the user into the address bar) cannot call getUserMedia(). These kinds of URLs loaded from JavaScript code inherit the script's permissions.
• Any other situation in which there is no origin, such as when the srcdoc attribute is used to specify the contents of a frame.

Generally, you will access the MediaDevices singleton object using navigator.mediaDevices, like this:

async function getMedia(constraints) {
  let stream = null;

  try {
    stream = await navigator.mediaDevices.getUserMedia(constraints);
    /* use the stream */
  } catch (err) {
    /* handle the error */
  }
}

Similarly, using the raw promises directly, the code looks like this:

navigator.mediaDevices
  .getUserMedia(constraints)
  .then((stream) => {
    /* use the stream */
  })
  .catch((err) => {
    /* handle the error */
  });

Below are some examples of the constraints parameter.

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

getUserMedia({
  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:

getUserMedia({
  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:

getUserMedia({
  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 OverconstrainedError, 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 full example:

getUserMedia({
  audio: true,
  video: {
    width: { min: 1024, ideal: 1280, max: 1920 },
    height: { min: 576, 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:

getUserMedia({
  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:

getUserMedia({
  audio: true,
  video: { facingMode: "user" },
});

To require the rear camera, use:

getUserMedia({
  audio: true,
  video: {
    facingMode: { exact: "environment" },
  },
});

Another non-number constraint is the deviceId constraint. If you have a deviceId from mediaDevices.enumerateDevices(), you can use it to request a specific device:

getUserMedia({
  video: {
    deviceId: myPreferredCameraDeviceId,
  },
});

The above will return the camera you requested, or a different camera if that specific camera is no longer available. Again, to require the specific camera, you would use:

getUserMedia({
  video: {
    deviceId: {
      exact: myExactCameraOrBustDeviceId,
    },
  },
});

This example gives a preference for camera resolution, and assigns the resulting MediaStream object to a video element.

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

navigator.mediaDevices
  .getUserMedia(constraints)
  .then((mediaStream) => {
    const video = document.querySelector("video");
    video.srcObject = mediaStream;
    video.onloadedmetadata = () => {
      video.play();
    };
  })
  .catch((err) => {
    // always check for errors at the end.
    console.error(`${err.name}: ${err.message}`);
  });

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

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

On mobile phones.

let front = false;
document.getElementById("flip-button").onclick = () => {
  front = !front;
};

const constraints = {
  video: { facingMode: front ? "user" : "environment" },
};

• The older Navigator.getUserMedia() legacy API
• MediaDevices.enumerateDevices(): Listing available media devices
• WebRTC API
• Media Capture and Streams API
• Screen Capture API: Capturing screen contents as a MediaStream
• MediaDevices.getDisplayMedia(): Getting a stream containing screen contents
• Taking webcam photos: A tutorial on using getUserMedia() to take still photos rather than video