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The WebRTC Screen Capture API lets a web app ask a person to choose a browser tab, application window, or display, then send the selected video through an RTCPeerConnection. The entry point is navigator.mediaDevices.getDisplayMedia(). It requires a secure context and a user-initiated action; the browser presents the source picker, and the user—not the page—chooses what to share.
How does WebRTC screen capture work?
getDisplayMedia() is a browser API for capturing a user-selected display surface. It resolves to a MediaStream, which your application can preview locally, record, or transmit through WebRTC. The method itself does not create a peer connection or signaling channel: your application still needs to establish the call and exchange connection information using its chosen signaling mechanism.
A typical outgoing share adds the captured video track to an existing RTCPeerConnection. If the call is already established, the peer connection can negotiate the new track as appropriate for your application. The screen-capture API does not prescribe that signaling workflow.
What must be in place before capture?
- Secure context: Serve the application in a secure context for the API to be available.
- Recent user action: Start capture directly from a user gesture, such as clicking a Share screen button. Do not defer the call to an unrelated later task.
- Browser support: Check the current compatibility information for every browser and version you intend to support. MDN labels the method “Limited availability”; browser and audio behavior are not uniform.
- Deployment policy: If Permissions Policy is configured, it must permit
display-capturefor the document. For an embedded app, check both the response policy and the iframe’s permissions. - Consent and clear UI: Explain what may be shared, show a visible sharing state, and provide an obvious way to stop.
Capture permission is not a reusable grant. The browser must let the user choose a display surface each time, and a site cannot silently choose or narrow the source picker with capture constraints. The W3C Screen Capture Working Draft published 27 August 2026 says the user agent “MUST let the end-user choose which display surface to share out of all available choices every time” and “MUST NOT use any MediaTrackConstraints in options.video or options.audio to limit that choice.” The document identifies itself as incomplete, subject to major changes, and not intended for implementation, so check its status and current browser documentation when shipping.
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How to share a screen with WebRTC
The following browser-side example assumes your application has already created an RTCPeerConnection named pc and attached its signaling flow. Connect the button to the handler from the page’s user interface.
const shareButton = document.querySelector("#share-screen");
const stopButton = document.querySelector("#stop-screen-share");
const preview = document.querySelector("#screen-preview");
const pc = new RTCPeerConnection(); // Add your ICE/signaling setup separately.
let screenStream;
let screenSender;
shareButton.addEventListener("click", async () => {
if (!navigator.mediaDevices?.getDisplayMedia) {
alert("Screen sharing is not available in this browser.");
return;
}
try {
// Keep this call directly inside the user-triggered handler.
screenStream = await navigator.mediaDevices.getDisplayMedia({ video: true });
preview.srcObject = screenStream;
preview.muted = true;
await preview.play().catch(() => {});
const [videoTrack] = screenStream.getVideoTracks();
if (!videoTrack) throw new Error("No screen video track was returned.");
screenSender = pc.addTrack(videoTrack, screenStream);
shareButton.disabled = true;
stopButton.disabled = false;
videoTrack.addEventListener("ended", stopSharing, { once: true });
} catch (error) {
if (error.name === "NotAllowedError") {
console.info("Screen sharing was declined or blocked by policy.");
} else {
console.error("Could not start screen sharing:", error);
}
}
});
stopButton.addEventListener("click", stopSharing);
function stopSharing() {
if (screenSender) {
pc.removeTrack(screenSender);
screenSender = undefined;
}
if (screenStream) {
screenStream.getTracks().forEach(track => track.stop());
screenStream = undefined;
}
preview.srcObject = null;
shareButton.disabled = false;
stopButton.disabled = true;
}Adapt connection setup and renegotiation to your app. If you add the track after the peer connection is already connected, your WebRTC signaling logic must handle the resulting negotiation. The preview is optional, but it helps confirm which stream your interface is sharing. The browser also provides its own sharing controls; your app should respond when the user stops sharing outside your page. The example listens for the video track’s ended event and clears its local state.
Optional screen audio
Audio capture is not guaranteed just because it was requested. Support can depend on the browser and selected surface. If your product offers audio, make it an explicit choice and describe what it captures; verify actual behavior in target browsers. For example, a request may be written as { video: true, audio: true }, but your application must still handle a stream that has no audio track. Do not assume every browser exposes the same audio sources or controls.
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Choose constraints without trying to choose the source
The browser’s picker owns the user’s source choice. Constraints and capture options can affect the resulting stream, but they cannot be used to silently restrict which surface the user may select. Do not design a workflow that assumes a particular tab or monitor will be picked just because the app requested capture.
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After capture begins, inspect the returned tracks and use supported track settings or WebRTC sender controls for the behavior your application needs. Keep feature detection and graceful handling in place: available options and resulting audio can vary by browser. Consult the MDN method reference and the W3C Screen Capture specification for current API details.
Permissions Policy for a page or embedded app
Permissions Policy can disable screen capture for a document. MDN documents display-capture with a default allowlist of self. If your app is embedded cross-origin, explicitly grant the feature to the intended frame with the relevant policy configuration and iframe allow attribute, then test the deployed response headers and embed configuration.
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A policy grant only allows the document to invoke the API; it does not replace the browser’s source picker or the user’s choice. If the policy disables capture, getDisplayMedia() fails with NotAllowedError. See MDN’s display-capture Permissions Policy reference and Screen Capture API implementation guide.
Protect the person sharing
A captured display may reveal messages, account details, browser tabs, or other material outside the intended presentation. Captured audio can reveal additional information. Before opening the picker, explain what sharing does; while it is active, make the state conspicuous and keep a stop control available. Where audio is optional, ask separately and explain its scope.
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Browser support and testing
There is no safe cross-browser promise that the same surfaces, audio, controls, and options are available everywhere. MDN currently marks getDisplayMedia() as “Limited availability” and advises checking compatibility, particularly for audio. Because exact support varies and changes, review the live compatibility table for your target browser versions rather than relying on a fixed version list.
Test at least the user flows your product will expose: canceling the picker, starting and stopping a share, ending it from the browser’s own control, selecting different surface types where offered, and sharing with and without audio where supported. Also test the actual deployed page and iframe policy rather than only a local development setup.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Troubleshooting common failures
| Symptom | Likely cause | What to check or do |
|---|---|---|
navigator.mediaDevices or getDisplayMedia is missing |
The page is not in a supported secure context, or the browser does not support the API. | Use a secure deployment and feature-detect the method. Check the current compatibility table for the browser and version. |
NotAllowedError |
The user canceled or declined, the request was not made from a recent user gesture, or Permissions Policy blocked the document. | Call from the Share button handler; inspect response policy and iframe allow settings; treat cancellation as a normal outcome rather than retrying without user action. |
| No audio track arrives | The browser or selected surface may not support audio capture, or the person did not select an audio-capable option. | Check stream.getAudioTracks().length, test target browsers, and communicate audio as optional rather than guaranteed. |
| The local preview is blank | The stream was not attached, playback did not start, or the share ended. | Set the video element’s srcObject to the returned stream, handle playback rejection, and listen for the track’s ended event. |
| The peer sees no screen video | The track was not added to the correct peer connection, or post-connection track negotiation/signaling did not complete. | Confirm pc.addTrack() ran for the captured video track and that your signaling implementation handles the new sender and negotiation. |
| The share stops unexpectedly | The user stopped sharing through browser controls, or the captured track ended. | Handle the track’s ended event, clear UI state, and let the user start a new capture through another explicit action. |
Or skip the browser setup
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Frequently Asked Questions
Can a website capture my screen without asking me?
No. The browser requires the user to choose a display surface for each capture; a web page cannot silently select one or retain a persistent display-capture grant.
Does requesting audio guarantee that screen audio will be shared?
No. Audio availability depends on browser support and the selected surface. Check the returned stream for an audio track and test the browsers you support.
Quick Recap
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