The MediaTrackConstraints dictionary's displaySurface property is a ConstrainDOMString describing the preferred value for the displaySurface constrainable property.

This is set by the application to identify to the user agent the type of display surface (window, browser, or monitor) preferred by the application. It has no effect on what the user can choose to share, but may be used to present the options in a different order.

If needed, you can determine whether or not this constraint is supported by checking the value of MediaTrackSupportedConstraints.displaySurface as returned by a call to MediaDevices.getSupportedConstraints(). However, typically this is unnecessary since browsers will ignore any constraints they're unfamiliar with.

A ConstrainDOMString which specifies the type of display surface preferred by the application. This value does not add or remove display sources in the browser's user interface, but may reorder them. You can't use this property to limit the user to a subset of the three display-surface values window, browser, and monitor — but, as you will see below, you can see what was chosen, and reject it.

See how constraints are defined.

You can check the setting selected by the user agent after the display media has been created by getDisplayMedia() by calling getSettings() on the display media's video MediaStreamTrack, then checking the value of the returned MediaTrackSettings object's displaySurface object.

For example, if your app prefers not to share a monitor — meaning that there's possibly a non-content backdrop being captured — it can use code similar to this:

let mayHaveBackdropFlag = false;
let displaySurface = displayStream
  .getVideoTracks()[0]
  .getSettings().displaySurface;

if (displaySurface === "monitor") {
  mayHaveBackdropFlag = true;
}

Following this code, mayHaveBackdrop is true if the display surface contained in the stream is of type monitor. Later code can use this flag to determine whether or not to perform special processing, such as to remove or replace the backdrop, or to "cut" the individual display areas out of the received frames of video.

Here are some example constraints objects for getDisplayMedia() that make use of the displaySurface property.

dsConstraints = { displaySurface: "window" }; // 'browser' and 'monitor' are also possible
applyConstraints(dsConstraints);
// The user still may choose to share the monitor or the browser,
// but we indicated that a window is preferred.

In addition, see the Constraint exerciser example that demonstrates how constraints are used.

• Screen Capture API
• Using the Screen Capture API
• Capabilities, constraints, and settings
• MediaTrackConstraints
• MediaDevices.getSupportedConstraints()
• MediaTrackSupportedConstraints