To capture a screen in a web app, call navigator.mediaDevices.getDisplayMedia() from a user-initiated action, show its returned MediaStream in a <video> element, and provide a clear way to stop sharing. The browser—not your page—lets the user choose a tab, window, or display. This demo covers local preview; recording and live delivery are separate steps.
What this demo does—and what it does not
The Screen Capture API provides the capture stream, not a saved video or a complete video-call system. MDN describes it as an extension to Media Capture and Streams that lets a user select a screen or portion of one, such as a window, for capture. You can preview that stream locally, record it with the MediaStream Recording API, or send it through WebRTC. Those are distinct outcomes with additional implementation requirements.
The example below requests video only. That keeps the first version focused: the user chooses a source, the page previews it, and either the page or the user stops sharing. A screen capture can show sensitive information, so make the sharing state visible and make the stop control easy to find.
Requirements before you start
- Use a secure context. Serve the page over HTTPS, or use a browser-recognized local development context.
- Start from a user action. Call
getDisplayMedia()directly in response to a click or another clear user gesture. Do not trigger it automatically on page load. - Allow the feature where necessary. A page restricted by Permissions Policy cannot capture. If the demo is embedded, the parent page may need to grant display capture to the iframe with its
allowattribute, as well as satisfy the applicable policy. - Check compatibility for your audience. Support is limited and varies by browser and operating system. Consult MDN’s live compatibility information for the browsers and versions you intend to support; do not promise universal availability.
The browser displays its own chooser and asks the user to confirm a source. Your site cannot silently select a screen, enumerate available screens like cameras, or narrow the chooser to force a specific source.
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Build a local screen-preview demo
Save this as an HTML file and serve it in a secure context. The page uses a button click to request capture, assigns the resulting stream to the video preview, and stops every track when the user selects Stop. It also reacts when the user ends sharing in browser chrome.
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Screen capture demo</title>
<style>
body { font: 16px/1.5 system-ui, sans-serif; max-width: 52rem; margin: 2rem auto; padding: 0 1rem; }
video { display: block; width: 100%; max-height: 70vh; background: #222; margin: 1rem 0; }
button { margin-right: .5rem; padding: .55rem .9rem; }
#status { min-height: 1.5em; }
</style>
</head>
<body>
<h1>Screen capture demo</h1>
<p>Choose what to share in the browser dialog. Check the selected screen for private information first.</p>
<button id="start" type="button">Start capture</button>
<button id="stop" type="button" disabled>Stop capture</button>
<p id="status" role="status" aria-live="polite">Not sharing.</p>
<video id="preview" autoplay playsinline muted></video>
<script>
const startButton = document.querySelector("#start");
const stopButton = document.querySelector("#stop");
const preview = document.querySelector("#preview");
const status = document.querySelector("#status");
let activeStream = null;
function setCaptureState(isSharing) {
startButton.disabled = isSharing;
stopButton.disabled = !isSharing;
status.textContent = isSharing ? "Sharing is active." : "Not sharing.";
}
function stopCapture() {
if (activeStream) {
activeStream.getTracks().forEach((track) => track.stop());
activeStream = null;
}
preview.srcObject = null;
setCaptureState(false);
}
async function startCapture() {
if (!navigator.mediaDevices?.getDisplayMedia) {
status.textContent = "Screen capture is not available in this browser or context.";
return;
}
try {
const stream = await navigator.mediaDevices.getDisplayMedia({
video: true,
audio: false,
});
activeStream = stream;
preview.srcObject = stream;
await preview.play();
const [videoTrack] = stream.getVideoTracks();
if (videoTrack) {
videoTrack.addEventListener("ended", stopCapture, { once: true });
}
setCaptureState(true);
} catch (error) {
if (error.name === "NotAllowedError") {
status.textContent = "Capture was cancelled or not permitted. Choose a source and allow sharing to continue.";
} else if (error.name === "NotFoundError") {
status.textContent = "No capturable display source was available.";
} else {
status.textContent = `Could not start capture: ${error.message || error.name}`;
}
setCaptureState(false);
}
}
startButton.addEventListener("click", startCapture);
stopButton.addEventListener("click", stopCapture);
</script>
</body>
</html>How the capture lifecycle works
- The user clicks Start capture, providing the required interaction.
- The browser opens its source picker. The user chooses and confirms a tab, window, or display.
- The promise resolves with a
MediaStream. The page assigns it topreview.srcObject;mutedavoids feedback from local playback. - Clicking Stop capture stops all stream tracks and clears the preview. If the user stops sharing from browser controls instead, the video track’s
endedevent resets the page state.
Cancellation and permission or policy failures are normal outcomes, not impossible states. The page should explain the result and let the user try again. The code is a minimal implementation pattern; test it in the browsers and embedding contexts you plan to support.
Recording, audio, and live sharing are separate choices
Local preview
The demo above only displays the stream in the current page. It does not upload or save the captured content.
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Recording for playback or download
To create a recording, pass the stream to the MediaStream Recording API’s MediaRecorder, collect the resulting data, and offer it for download or send it to a storage service. Choose a MIME type supported by the target browser, checking support rather than assuming a single format works everywhere. The capture API itself does not provide a recording-storage service.
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Sharing with another person
For live remote sharing, add a WebRTC connection and the surrounding application flow, including a way for participants to establish the connection. getDisplayMedia() supplies the local stream; it is not a signaling service or a complete conferencing system.
Requesting audio
Set audio: true only if the demo needs to request audio. The browser may still return no audio track: availability depends on browser, platform, and the surface the user chooses. Inspect stream.getAudioTracks().length before displaying an audio-enabled state. Do not promise system audio until you have validated the browser-and-OS combinations you support.
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Options and source-selection limits
The options passed to getDisplayMedia() can express preferences or request tracks, but they do not replace the browser’s source picker. Hints such as preferring the current tab or offering surface switching may affect browser behavior where supported; they cannot force the user to share a particular tab or hide other eligible choices. Check the current MDN method reference before relying on a particular option across browsers.
| Decision | What it means for the demo |
|---|---|
| Tab, window, or full display | The user chooses in browser UI. A full display can expose more background content; a tab can limit what is visible, but the page cannot silently force the choice. |
| Video only or request audio | Video-only is a simpler starting point. Requested audio may be absent, depending on browser, operating system, and selected surface. |
| Native API or an abstraction | The browser-native API is enough for a small preview demo. Consider a third-party layer only if a larger product needs broader browser handling, transport, recording infrastructure, or support. |
Privacy and interface details that matter
- Tell users what the capture is for before the browser chooser opens.
- Remind them to close sensitive documents, messages, or background windows they do not intend to expose.
- Show a clear active-sharing state and keep Stop visible while capture is running.
- Handle browser-side stopping so the page does not falsely claim capture is still active.
- Request only the tracks the feature needs. Do not imply that a browser permission grants access to a hidden or preselected source.
The browser controls its sharing indicator and confirmation interface. Your page should complement those safeguards with honest status and an obvious exit.
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Troubleshooting common failures
getDisplayMediais undefined: The browser may not support the API, the page may not be in a secure context, or the feature may be unavailable in that environment. Checkwindow.isSecureContext, use HTTPS or an appropriate local context, and check compatibility for the target browser.- The request fails inside an iframe: Check the parent document’s Permissions Policy for
display-captureand the iframe’sallowattribute. The embedding site may need to explicitly permit capture. - The chooser does not appear: Call the method directly from a fresh user action. An automatic page-load call or delayed action may not retain the required transient user activation.
- The user cancels or denies the chooser: Treat this as an expected outcome. Keep the interface usable, explain that no source was shared, and let the user initiate another request.
- The video is blank or playback rejects: Confirm the request resolved, that the stream has a video track, and that it was assigned to
srcObject. Awaitpreview.play()and report a playback error instead of silently claiming success. - Audio is missing: Check
stream.getAudioTracks(). A successful video capture does not guarantee that the selected surface or browser provides audio. - The page still says sharing after the user stops in browser chrome: Listen for the capture track’s
endedevent and reset the buttons, status, and preview, as the example does.
Performance and reliability notes
Screen capture can involve large, changing frames, so avoid adding recording, encoding, or network transmission until the preview flow works. Those later steps have their own CPU, memory, bandwidth, and storage implications; the browser capture API does not remove those costs. Stop tracks as soon as the user is done, and test the behavior on the actual browser and operating-system combinations your app supports. There is no single cross-browser guarantee for audio or every chooser option.
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Or skip the browser setup
If what you need is a screenshot of a web page rather than a live, user-selected desktop stream, ScreenshotNeo provides a website screenshot API and MCP server for developers. One GET request returns a PNG, JPEG, WebP, or PDF. For example, this cURL request saves a WebP capture of Stripe:
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Frequently Asked Questions
Can a web page choose the screen or tab for the user?
No. The browser’s own chooser controls source selection and asks the user to confirm.
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Does the Screen Capture API save a video file?
No. It returns a stream. Recording and storage require additional APIs and application logic.
Will requesting audio always capture system sound?
No. Audio availability varies by browser, operating system, and selected surface.
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