The WebRTC Screen Capture API lets a web page ask a user to choose a browser tab, application window, or display, then receive the selection as a MediaStream. Call navigator.mediaDevices.getDisplayMedia() from a secure, user-initiated action, attach the returned video track to an RTCPeerConnection, and handle the user stopping or denying the share. The browser—not your constraints—controls which source the user can select.
What the WebRTC Screen Capture API does
The API is centered on MediaDevices.getDisplayMedia(), specified by the W3C Screen Capture specification. A successful call resolves to a MediaStream. You can preview it in a video element, record it, or send its tracks through WebRTC.
The current W3C document is a Working Draft dated 27 August 2026 and warns that it is incomplete and may change. Treat browser behavior as an implementation detail to verify against current compatibility data when you deploy.
Minimal working example
This complete page starts capture only after a button click, previews the stream locally, sends the video track to a peer connection, and reacts when sharing ends.
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<button id="share">Share screen</button>
<button id="stop" disabled>Stop sharing</button>
<video id="preview" autoplay muted playsinline></video>
<p id="status" role="status"></p>
<script>
const shareButton = document.querySelector('#share');
const stopButton = document.querySelector('#stop');
const preview = document.querySelector('#preview');
const status = document.querySelector('#status');
const peer = new RTCPeerConnection();
let displayStream;
shareButton.addEventListener('click', async () => {
try {
displayStream = await navigator.mediaDevices.getDisplayMedia({
video: true,
audio: false
});
preview.srcObject = displayStream;
const [videoTrack] = displayStream.getVideoTracks();
peer.addTrack(videoTrack, displayStream);
videoTrack.addEventListener('ended', () => {
preview.srcObject = null;
shareButton.disabled = false;
stopButton.disabled = true;
status.textContent = 'Screen sharing stopped.';
});
shareButton.disabled = true;
stopButton.disabled = false;
status.textContent = 'You are sharing your selected display surface.';
} catch (error) {
status.textContent = `${error.name}: ${error.message}`;
}
});
stopButton.addEventListener('click', () => {
displayStream?.getTracks().forEach(track => track.stop());
});
</script>In a real call, complete your normal WebRTC signaling and offer/answer exchange after addTrack(). The capture API supplies media; it does not provide signaling, a server, or a remote video element.
Requirements before calling getDisplayMedia()
Use a secure context
Serve the page over HTTPS. During local development, browsers commonly treat localhost as trustworthy, but test the exact deployment origin you will use. If navigator.mediaDevices is unavailable, check the context before debugging WebRTC.
Require recent user interaction
Invoke the method directly from a button or other recent user gesture. A timer, page-load handler, or delayed promise chain can be rejected. The browser must present a picker each time; a site cannot silently reuse a permanent display-capture grant.
Allow the document under Permissions Policy
The default display-capture allowlist is self. If you set a Permissions-Policy header or embed the app, permit the feature explicitly:
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<iframe src="https://app.example" allow="display-capture"></iframe>Policy permission only makes the API available. The user still chooses the surface and can cancel. A disabled policy causes NotAllowedError; see the MDN display-capture policy reference.
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Choosing video and audio
Video is the share surface
Use video: true to request display video. The picker may offer a tab, window, or monitor, depending on the browser and operating system. Do not describe those choices as universally available.
Audio is conditional
You can request audio with audio: true, but that is not a guarantee that audio will be captured. Support depends on the browser, operating system, selected surface, and current implementation. Keep the audio choice visible in your UI and explain whether tab or system audio is expected.
const stream = await navigator.mediaDevices.getDisplayMedia({
video: true,
audio: true
});
const audioTracks = stream.getAudioTracks();
if (audioTracks.length === 0) {
// Tell the user that this browser or selected surface supplied no audio.
}Review the MDN getDisplayMedia documentation and the MDN Screen Capture usage guide for current browser-specific audio notes.
Why constraints cannot select a source
Display capture is intentionally user-controlled. The W3C requirement says the user agent must let the end user choose from available display surfaces every time and must not use MediaTrackConstraints in options.video or options.audio to limit that choice. In practice, constraints can influence the resulting track after selection, but they cannot silently force “this monitor” or suppress the picker.
For example, this asks for a preferred frame rate after the user chooses a source; it does not select the source:
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const stream = await navigator.mediaDevices.getDisplayMedia({
video: { frameRate: { ideal: 30, max: 60 } },
audio: false
});Sending the capture through WebRTC
- Call
getDisplayMedia()in the click handler. - Set a local preview with
video.srcObject = streamso the sharer can see what is live. - Add each track to your existing
RTCPeerConnectionwithpeer.addTrack(track, stream). - Create or renegotiate an offer, send it through your signaling channel, and apply the remote answer.
- On the receiving peer, render the incoming stream in a separate video element.
- Listen for the capture track’s
endedevent. The user can stop sharing from browser chrome even when your page does nothing.
If you are replacing a camera track rather than adding a second video, use the connection’s sender and RTCRtpSender.replaceTrack() in your application logic. Stop old tracks when they are no longer needed.
Privacy and consent design
- Show a persistent “sharing” state and identify whether the app is sending a tab, window, or entire display.
- Provide an obvious stop button, while also handling the browser’s own stop control.
- Warn users that notifications, passwords, private documents, and other windows visible on the selected display may be exposed.
- Explain audio separately; users may expect video sharing without sound.
- Do not imply that cross-origin content is automatically safe. Captured browser content can reveal information protected by cross-origin restrictions.
The MDN Screen Capture API overview and the W3C security guidance describe these disclosure risks. Elevated permissions discussed by the specification are implementation advice, not a universal application-controlled switch.
Browser support and deployment decisions
MDN labels getDisplayMedia() “Limited availability” and not Baseline because it does not work in some widely used browsers. There is no single guarantee that every browser exposes the same source types, controls, or audio behavior. Check the current compatibility table for every browser and version you support, then test:
| Decision | What to verify |
|---|---|
| Surface | Whether tab, window, and full-display choices appear in the target browser and operating system. |
| Audio | Whether the selected surface can provide audio and how the browser labels consent. |
| Policy | Whether headers and iframe permissions allow display-capture. |
| UX | How users stop sharing and how your app detects the ended track. |
Common errors and fixes
NotAllowedError
The user may have cancelled, the call may not have followed a user gesture, the context may be insecure, or Permissions Policy may block the document. Use HTTPS, call from a visible click handler, inspect response headers and iframe attributes, and tell the user exactly what was cancelled.
TypeError or an unavailable API
Check that the options are valid, that the page is secure, and that the target browser implements the API. Feature-detect before rendering the share control:
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const canShareDisplay = !!navigator.mediaDevices?.getDisplayMedia;
shareButton.hidden = !canShareDisplay;Video works but audio is missing
The browser or selected surface may not support audio capture, or the user may have declined it. Inspect stream.getAudioTracks(), explain the limitation, and offer a browser-specific fallback such as sharing a tab when that is supported.
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Stopping a display track ends the source. Handle track.onended, notify the peer, and remove or replace the sender in your call state instead of assuming the stream remains reusable.
An iframe cannot start capture
Confirm the top-level Permissions Policy, the iframe’s allow="display-capture", and the origin listed by the header. Policy access does not bypass the picker.
Performance and reliability considerations
Full-display video can produce substantial bandwidth and CPU use. Negotiate an appropriate resolution and frame rate after selection, avoid showing unnecessary duplicate previews, and monitor outbound WebRTC statistics in your existing call diagnostics. Keep the UI responsive while waiting for the picker; the user may take time to choose.
Design for cancellation and intermittent support rather than retrying automatically. A fresh call should produce a fresh user choice. For recordings, retain the same ended-track handling and close the recorder when all relevant tracks stop.
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Or skip the browser setup
If your goal is a static website image rather than an interactive user-approved screen share, ScreenshotNeo is a simpler API. It renders a URL on its service and returns PNG, JPEG, WebP, or PDF; it does not capture a visitor’s private monitor.
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Further reading
- W3C Screen Capture Working Draft
- MDN MediaDevices.getDisplayMedia()
- MDN display-capture Permissions Policy
- MDN Screen Capture API
- MDN Using the Screen Capture API
Frequently Asked Questions
Can a website capture my screen without asking?
No. The browser must let you choose a display surface each time; a page cannot silently select or persist a display-capture permission.
Does getDisplayMedia() work from an HTTP page?
Use a secure context, normally HTTPS. Test localhost separately during development because browser trust rules can differ.
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Can I capture only one application automatically?
No. Your code cannot use constraints to narrow the picker. The user chooses the available tab, window, or display.
Why does the browser show a picker on every call?
The Screen Capture rules require a fresh end-user choice for each capture request, rather than a permanent grant.
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