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To save a frame from an Electron video stream, assign the stream to an HTML <video> element, wait until it has decoded metadata, draw that frame onto a canvas, and encode the canvas as PNG (or another format). Electron supplies the desktop or window MediaStream; the renderer’s video element and Canvas API produce the still image.
What the capture pipeline does
The reliable sequence is:
- Obtain a desktop or window source with Electron’s display-capture APIs.
- Expose the resulting
MediaStreamto the renderer. - Set
video.srcObjectand start playback. - Wait for non-zero intrinsic dimensions.
- Copy the decoded frame with
ctx.drawImage(video, ...). - Encode the canvas as a data URL, Blob, or file.
Electron’s desktopCapturer documentation describes the source-enumeration API, while its display-capture example shows the stream-to-video setup. The Canvas drawImage() documentation lists HTMLVideoElement as a valid image source.
Choose a desktop or window source
Use the system picker
navigator.mediaDevices.getDisplayMedia() can open the operating system’s display picker. This is the appropriate path when the user should choose a monitor or window interactively. Electron notes that getDisplayMedia() does not accept a deviceId to silently select a source; selection belongs to the display-capture flow.
Preselect an Electron source
When your application needs to present its own source list, call desktopCapturer.getSources({ types: ['screen', 'window'] }). Each returned DesktopCapturerSource represents a screen or individual window. Configure Electron’s display-media request handler in the main process, then allow the renderer to request the stream.
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- 【Package Content & Note】 1x HD Audio Capture Card , 1x USB 3.0 to USB C Adapter (A-side 3.0, B-side 2.0), 1x user manual. Please note that you need to restart the OBS Studio software after the audio setup is complete, otherwise it will result in no sound output. When using an adapter, if the device is recognized as USB 2.0, try using the other side with the USB-C port. Simply flip the capture card and reconnect it to be recognized as USB 3.0
A minimal main-process setup (adapt the selection policy to your UI) is:
const { app, session, desktopCapturer } = require('electron');
app.whenReady().then(() => {
session.defaultSession.setDisplayMediaRequestHandler(async (request, callback) => {
const sources = await desktopCapturer.getSources({
types: ['screen', 'window']
});
// Replace this with a user-selected source from your application UI.
const source = sources[0];
if (!source) {
callback({ video: null });
return;
}
callback({ video: source });
});
});In production, do not assume sources[0] is the desired display. Show the source names and thumbnails, let the user choose, and handle cancellation.
Renderer request
After the handler is installed, the renderer can request display media:
async function getDisplayStream() {
return navigator.mediaDevices.getDisplayMedia({
video: true,
audio: false
});
}Keep the returned stream in application state. Its video track is also how you detect that the user stopped sharing.
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Put a video and canvas in the renderer page:
<video id="preview" autoplay muted playsinline></video>
<canvas id="frameCanvas" hidden></canvas>The following implementation waits for media data, sizes the canvas to decoded pixels rather than CSS dimensions, and returns a PNG data URL:
const video = document.querySelector('#preview');
const canvas = document.querySelector('#frameCanvas');
const ctx = canvas.getContext('2d');
async function attachStream(stream) {
video.srcObject = stream;
await video.play();
await new Promise((resolve) => {
if (video.readyState >= HTMLMediaElement.HAVE_CURRENT_DATA) {
resolve();
} else {
video.addEventListener('loadeddata', resolve, { once: true });
}
});
canvas.width = video.videoWidth;
canvas.height = video.videoHeight;
}
function capturePng() {
if (!video.videoWidth || !video.videoHeight) {
throw new Error('No decoded video frame is available yet');
}
canvas.width = video.videoWidth;
canvas.height = video.videoHeight;
ctx.drawImage(video, 0, 0, canvas.width, canvas.height);
return canvas.toDataURL('image/png');
}
async function startCapture() {
const stream = await navigator.mediaDevices.getDisplayMedia({
video: true,
audio: false
});
await attachStream(stream);
const pngDataUrl = capturePng();
document.querySelector('#result').src = pngDataUrl;
stream.getVideoTracks()[0].addEventListener('ended', () => {
video.srcObject = null;
});
return { stream, pngDataUrl };
}Add <img id="result" alt="Captured frame"> and call startCapture() from a user-activated button. Calling getDisplayMedia() outside an appropriate user gesture can be rejected by the platform.
Download the PNG
A data URL is convenient for previews and small captures:
function downloadDataUrl(dataUrl, filename = 'frame.png') {
const link = document.createElement('a');
link.href = dataUrl;
link.download = filename;
link.click();
}For large frames or binary workflows, use a Blob instead of keeping a long base64 string in memory:
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- 【Support Mic-in for Commentary】Rybozen capture card has microphone input and you can use it to add external commentary when playing a game. Please note: it only accepts 3.5mm TRS standard microphone headset.
function canvasToBlob(type = 'image/png', quality) {
return new Promise((resolve, reject) => {
canvas.toBlob((blob) => {
if (blob) resolve(blob);
else reject(new Error('Canvas encoding failed'));
}, type, quality);
});
}
async function saveBlob(blob, filename = 'frame.png') {
const url = URL.createObjectURL(blob);
const link = document.createElement('a');
link.href = url;
link.download = filename;
link.click();
URL.revokeObjectURL(url);
}In an Electron app that needs a native path, send the Blob’s bytes through your preload bridge to a main-process file-save routine. Keep Node integration disabled in untrusted renderer content.
Capture an exact or repeated video frame
A button capture takes the frame currently available to the video element. For animation, synchronization, or a frame-timed grab, use requestVideoFrameCallback(). MDN defines this callback as running when a new video frame is sent to the compositor.
function captureNextFramePng() {
return new Promise((resolve, reject) => {
if (!('requestVideoFrameCallback' in HTMLVideoElement.prototype)) {
try {
resolve(capturePng());
} catch (error) {
reject(error);
}
return;
}
video.requestVideoFrameCallback(() => {
try {
resolve(capturePng());
} catch (error) {
reject(error);
}
});
});
}
async function captureLoop() {
const png = await captureNextFramePng();
// Store or process png here, then schedule another iteration if required.
return png;
}The fallback matters for older embedded Chromium versions. MDN records broad availability of requestVideoFrameCallback() from October 2024, but an Electron application can still run a runtime that predates it. Check the prototype as shown rather than assuming support.
Avoid the zero-dimension race
video.videoWidth or video.videoHeight equal to zero means no usable decoded frame is available. Wait for loadeddata, call play(), or wait for the next video-frame callback before drawing. Do not size the canvas from the element’s CSS width and height if you want the source’s decoded pixel dimensions.
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Stop every video track when the user finishes, then detach the stream:
function stopCapture(stream) {
for (const track of stream.getVideoTracks()) {
track.stop();
}
video.srcObject = null;
}Stopping tracks releases the display-capture session and prevents a hidden video element from retaining resources. Also remove any frame callbacks or application timers used by a capture loop.
Platform permissions and source behavior
macOS
Electron documents that screen-content capture requires user consent on macOS 10.15 and later. Detect denial and explain how to enable your application in the system’s Screen Recording privacy settings; do not treat an empty source as a successful capture.
Linux with PipeWire
Electron documents a PipeWire caveat: requesting both screen and window types can return only one capture, and the selected source is treated as a window capture in that situation. Test your source-list logic on the desktop environments you support, and offer a clear fallback when the expected monitor/window distinction is unavailable.
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Other operating systems
Display-picker UI, consent prompts, and window-visibility rules are platform controlled. Handle rejected promises, an ended track, and a source that disappears before the frame is decoded. Never promise that minimized, protected, or permission-restricted windows will produce pixels.
Troubleshooting
NotAllowedError or a cancelled picker
Cause: The user denied capture, cancelled the picker, or the request was not made from an allowed user action. Fix: Catch the rejection, keep the UI in an idle state, and retry from a clearly labelled button.
The canvas is blank
Cause: Drawing happened before playback or before decoded dimensions became non-zero. Fix: await video.play(), wait for loadeddata or requestVideoFrameCallback(), and verify video.videoWidth and video.videoHeight.
The image is the wrong size
Cause: The canvas was sized from CSS pixels or a fixed preview size. Fix: set both canvas dimensions from video.videoWidth and video.videoHeight immediately before drawing.
The first frame is stale
Cause: A draw call ran between compositor updates. Fix: use requestVideoFrameCallback() for frame-timed captures; otherwise capture after playback has produced current data.
Capture continues after the window closes
Cause: Tracks and references were left running. Fix: call track.stop() for every video track, set video.srcObject = null, and stop your capture loop.
Only one kind of source appears on Linux
Cause: PipeWire’s documented behavior when both screen and window types are requested. Fix: account for the returned source type and test separate requests if your product requires distinct choices.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Performance, format, and reliability choices
- Pixel dimensions: Intrinsic video dimensions preserve the decoded frame; very large displays consume more memory when copied to canvas.
- Encoding: PNG is lossless and widely usable. JPEG or WebP can reduce file size by passing a different MIME type to
toDataURL()ortoBlob(); lossy formats accept an optional quality value. - Data URL versus Blob: Data URLs simplify previews but add base64 overhead. Blobs are preferable for uploads, repeated captures, and native file handling.
- Repeated capture: Use frame callbacks rather than an unconstrained timer so work tracks compositor updates. Throttle processing if encoding takes longer than the frame interval.
- Security: Restrict capture to an explicit user action, keep privileged APIs behind a preload bridge, and validate any source-selection messages crossing IPC.
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Install the request in your app (see the ScreenshotNeo documentation):
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FAQ
Can Electron return a PNG directly from desktopCapturer?
No. It provides capture sources and a media stream. The renderer must decode the stream and perform the video-to-canvas conversion.
Can I capture only part of a window?
The documented source APIs select screens or windows. For a region, draw the desired rectangle from the video onto a smaller canvas using the source and destination rectangle form of drawImage().
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Why does a CSS-scaled video not improve screenshot resolution?
CSS changes presentation size, not decoded pixels. The screenshot’s maximum source detail is governed by video.videoWidth and video.videoHeight.
Frequently Asked Questions
Can Electron return a PNG directly from desktopCapturer?
No. It provides capture sources and a media stream; the renderer must draw the decoded video frame onto a canvas and encode it.
Can I capture only part of a window?
Yes. Draw a source rectangle into a smaller canvas with the source-and-destination form of Canvas drawImage().
Why does CSS scaling not increase screenshot resolution?
CSS changes display size, while output detail is limited by the video’s intrinsic decoded dimensions.
Quick Recap
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