MediaDevices.getDisplayMedia()
The MediaDevices
interface's
getDisplayMedia()
method prompts the user to select and
grant permission to capture the contents of a display or portion thereof (such as a
window) as a MediaStream
.
The resulting stream can then be recorded using the MediaStream Recording API or transmitted as part of a WebRTC session.
See Using the Screen Capture API for more details and an example.
Syntax
var promise = navigator.mediaDevices.getDisplayMedia(constraints);
Parameters
constraints
Optional-
An optional object specifying requirements for the returned
MediaStream
. SincegetDisplayMedia()
requires a video track, the returned stream will have one even if no video track is expressly requested by theconstraints
object. For more details, see the constraints section under theMediaDevices.getUserMedia()
method, as well as the article Capabilities, constraints, and settings.
Return value
A Promise
that resolves to a MediaStream
containing a
video track whose contents come from a user-selected screen area, as well as an optional
audio track.
Note: Browser support for audio tracks varies, both in terms of whether or not they're supported at all by the media recorder and in terms of the audio sources supported. Check the compatibility table for details for each browser.
Exceptions
AbortError
DOMException
-
Returned if an error or failure does not match any of the other exceptions listed here.
InvalidStateError
DOMException
-
Returned if the call to
getDisplayMedia()
was not made from code running due to a user action, such as an event handler. Another potential cause for this event: thedocument
in whose contextgetDisplayMedia()
was called is not fully active; for example, perhaps it is not the frontmost tab. NotAllowedError
DOMException
-
Returned if the permission to access a screen area was denied by the user, or the current browsing instance is not permitted access to screen sharing.
NotFoundError
DOMException
-
Returned if no sources of screen video are available for capture.
NotReadableError
DOMException
-
Returned if the user selected a screen, window, tab, or other source of screen data, but a hardware or operating system level error or lockout occurred, preventing the sharing of the selected source.
OverconstrainedError
DOMException
-
Returned if, after creating the stream, applying the specified
constraints
fails because no compatible stream could be generated. TypeError
DOMException
-
Returned if the specified
constraints
include constraints which are not permitted when callinggetDisplayMedia()
. These unsupported constraints areadvanced
and any constraints which in turn have a member namedmin
orexact
.
Usage notes
Privacy and security
Because getDisplayMedia()
could be used in nefarious ways, it can be a
source of significant privacy and security concerns. For that reason, the specification
details measures browsers are required to take in order to fully support
getDisplayMedia()
.
-
The specified
constraints
can't be used to limit the options available to the user. Instead, they must be applied after the user chooses a source, in order to generate output that matches the constraints. -
The go-ahead permission to use
getDisplayMedia()
cannot be persisted for reuse. The user must be prompted for permission every time. -
The call to
getDisplayMedia()
must be made from code which is running in response to a user action, such as in an event handler. - Browsers are encouraged to provide a warning to users about sharing displays or windows that contain browsers, and to keep a close eye on what other content might be getting captured and shown to other users.
Example
In the example below, a startCapture()
method is created which initiates
screen capture given a set of options specified by the displayMediaOptions
parameter. The options are specified in an object which specifies the preferred stream
configuration and the display
surface from which video is to be captured.
async function startCapture(displayMediaOptions) {
let captureStream = null;
try {
captureStream = await navigator.mediaDevices.getDisplayMedia(displayMediaOptions);
} catch(err) {
console.error("Error: " + err);
}
return captureStream;
}
This uses await
to asynchronously wait for getDisplayMedia()
to resolve with a MediaStream
which contains the display contents as
requested by the specified options. The stream is then returned to the caller for use,
perhaps for adding to a WebRTC call using RTCPeerConnection.addTrack()
to
add the video track from the stream.
Specifications
Specification |
---|
Screen Capture # dom-mediadevices-getdisplaymedia |
Browser compatibility
BCD tables only load in the browser
See also
- Screen Capture API
- Using the Screen Capture API
- Media Capture and Streams API
- WebRTC API
-
getUserMedia()
: Capturing media from a camera and/or microphone