To capture a video frame in JavaScript, pass the video element to the Canvas 2D context’s drawImage() method. For the frame at a particular time, seek the video and wait until the requested frame is ready before drawing. For ongoing frame-by-frame work, use requestVideoFrameCallback() where supported.
Capture the video’s current frame
The basic operation is ctx.drawImage(video, x, y, width, height). An HTMLVideoElement is a valid image source, so the canvas receives the video’s currently available frame. Set the canvas dimensions after the video metadata loads, then draw only when media data is available.
<video id="video" src="clip.mp4" muted playsinline controls></video>
<canvas id="canvas"></canvas>
<script>
const video = document.querySelector("#video");
const canvas = document.querySelector("#canvas");
const ctx = canvas.getContext("2d");
video.addEventListener("loadedmetadata", () => {
canvas.width = video.videoWidth;
canvas.height = video.videoHeight;
});
function drawCurrentFrame() {
if (video.readyState < HTMLMediaElement.HAVE_CURRENT_DATA) {
throw new Error("The video does not have frame data available yet.");
}
ctx.drawImage(video, 0, 0, canvas.width, canvas.height);
}
video.addEventListener("loadeddata", drawCurrentFrame, { once: true });
</script>video.videoWidth and video.videoHeight are the video’s intrinsic dimensions. The canvas width and height set its backing resolution; changing them also clears its contents and resets context state, so set them before drawing. If you want a smaller output, set a smaller canvas size and use the destination-size form of drawImage(), as above.
MDN documents the video element as a drawImage() source and notes that media readiness must be greater than 1 (HAVE_CURRENT_DATA) for drawing to work correctly. See MDN’s drawImage() documentation.
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Capture a frame at a specific timestamp
Assign the target time to video.currentTime, then wait for the seek to finish before drawing. The following function handles repeated requests by removing the previous seek listener, rejects out-of-range times, and returns a promise you can await.
let pendingSeekCleanup;
function captureAt(video, canvas, seconds) {
const ctx = canvas.getContext("2d");
if (!Number.isFinite(seconds) || seconds < 0 || seconds > video.duration) {
return Promise.reject(new RangeError("Requested time is outside the video."));
}
if (pendingSeekCleanup) pendingSeekCleanup();
return new Promise((resolve, reject) => {
let timer;
const cleanup = () => {
clearTimeout(timer);
video.removeEventListener("seeked", onSeeked);
video.removeEventListener("error", onError);
if (pendingSeekCleanup === cleanup) pendingSeekCleanup = undefined;
};
const onError = () => {
cleanup();
reject(new Error("Video failed while seeking."));
};
const onSeeked = () => {
if (video.readyState < HTMLMediaElement.HAVE_CURRENT_DATA) return;
cleanup();
canvas.width = video.videoWidth;
canvas.height = video.videoHeight;
ctx.drawImage(video, 0, 0, canvas.width, canvas.height);
resolve(canvas);
};
pendingSeekCleanup = cleanup;
video.addEventListener("seeked", onSeeked);
video.addEventListener("error", onError, { once: true });
timer = setTimeout(() => {
cleanup();
reject(new Error("Timed out waiting for the requested frame."));
}, 15000);
video.currentTime = seconds;
});
}
// Example, after metadata is loaded:
await captureAt(video, canvas, 4.25);The example replaces an earlier pending seek callback when a newer request arrives. If your application must complete every requested capture, rather than keeping only the newest one, serialize requests in a queue instead. A seek event indicates the seek operation completed; the readiness check guards against drawing before current frame data is available. MDN’s canvas image tutorial demonstrates seeking and recommends using requestVideoFrameCallback() to ensure a frame is ready.
Seeking is to a media time, not necessarily an exact encoded frame index. For frame-accurate extraction, account for the source’s frame rate and keyframe structure, and verify the result in the target browsers and media. The APIs described here provide browser rendering of a video frame; they do not promise exact synchronization with a separate clock or playback pipeline.
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Crop or scale the captured frame
drawImage() has overloads for positioning, scaling, and cropping. Use the 3-argument form to draw at the source’s natural dimensions, the 5-argument form to scale to a destination rectangle, or the 9-argument form to select a source rectangle and map it to a destination rectangle.
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// Scale the full frame to a 640 × 360 canvas.
canvas.width = 640;
canvas.height = 360;
ctx.drawImage(video, 0, 0, 640, 360);
// Crop a 320 × 180 region beginning at (100, 50), then scale it.
ctx.drawImage(video, 100, 50, 320, 180, 0, 0, canvas.width, canvas.height);Coordinates in the source rectangle refer to the video image; destination coordinates and dimensions refer to the canvas. For a crop that should retain its natural size, make the canvas match the crop dimensions. For a scaled crop, set the canvas to the desired output dimensions.
Process frames as the video plays
For overlays, analysis, or repeated canvas updates, schedule the next callback from the current callback. That ties work to new video frames rather than polling with a generic timer.
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function onVideoFrame(now, metadata) {
if (video.readyState >= HTMLMediaElement.HAVE_CURRENT_DATA) {
ctx.drawImage(video, 0, 0, canvas.width, canvas.height);
}
// metadata includes information about this presented video frame.
video.requestVideoFrameCallback(onVideoFrame);
}
if ("requestVideoFrameCallback" in HTMLVideoElement.prototype) {
video.requestVideoFrameCallback(onVideoFrame);
} else {
// Use a fallback selected for the browsers your application supports.
}The callback receives a high-resolution timestamp and frame metadata. MDN describes requestVideoFrameCallback() as running when a new video frame is sent to the compositor. Its cadence is bounded by the lower of the video frame rate and browser paint refresh rate; it may run a vertical synchronization late, so it is not a hard real-time guarantee. Feature-detect it rather than assuming every browser version has it. MDN labels the API Baseline 2024—available on the latest devices and browser versions since October 2024—while noting that older versions or devices may not support it. Details: MDN requestVideoFrameCallback().
If a fallback based on requestAnimationFrame() is suitable, it can draw on display refreshes, but it is not inherently synchronized to each distinct video frame. Avoid using a fixed interval as if it guaranteed frame accuracy.
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| Need | Approach | Important trade-off |
|---|---|---|
| One still from the frame currently displayed | Call drawImage(video, ...) when current frame data is ready. |
Simple; depends on media readiness. |
| A still at a chosen time | Set currentTime, wait for seeking and available frame data, then draw. |
Seeking and readiness need handling. |
| Repeated frame-triggered work | Draw inside requestVideoFrameCallback(). |
Frame-oriented but not perfectly synchronized; older environments may lack support. |
| Advanced decoded-frame processing | Use WebCodecs VideoFrame with a canvas rendering method. |
More involved; Canvas 2D behavior and performance can vary by browser. |
For WebCodecs background and usage guidance, consult MDN’s Using the WebCodecs API and VideoFrame references.
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Export the canvas image
Once the frame has been drawn, use canvas.toBlob() to encode it as an image without building a large data URL string. The browser may choose a fallback format if it does not support the requested type.
function canvasToBlob(canvas, type = "image/png", quality) {
return new Promise((resolve, reject) => {
canvas.toBlob(blob => {
if (blob) resolve(blob);
else reject(new Error("Canvas image encoding failed."));
}, type, quality);
});
}
const blob = await canvasToBlob(canvas, "image/jpeg", 0.9);
const imageUrl = URL.createObjectURL(blob);
const link = document.createElement("a");
link.href = imageUrl;
link.download = "video-frame.jpg";
link.click();
URL.revokeObjectURL(imageUrl);Use PNG for lossless output or when transparency matters; JPEG is lossy. If the video is cross-origin, the server must permit the relevant cross-origin access and the video must be configured for CORS before loading if you intend to export pixels. Otherwise, drawing may be possible while reading or exporting canvas pixels is blocked by browser security protections. Set the video’s crossOrigin property before assigning its source and configure the media server’s CORS response appropriately.
Troubleshoot blank captures and timing errors
- The canvas is blank: confirm metadata loaded, dimensions are nonzero, and
readyState >= HTMLMediaElement.HAVE_CURRENT_DATA. Draw afterloadeddatafor an initial frame or after the seek and frame readiness for a timestamp capture. - The image is stretched or blurry: check that canvas backing dimensions reflect the intended output and that destination width and height preserve the source aspect ratio. Increasing CSS display size alone does not increase canvas resolution.
- A seek callback never resolves: check that the requested time is within the finite duration, listen for media errors, and provide a timeout. Live streams may have an unknown duration or a moving seekable range; a timestamp outside the currently seekable range cannot be captured by simply assigning it.
- Two captures return the wrong frame: overlapping seeks can race. Serialize them or cancel the previous pending listener when replacing a request, then draw only after the completed seek’s data is ready.
- Export throws a security error: the canvas may be tainted by a cross-origin video. Configure CORS on both the element request and the media server before drawing; JavaScript cannot bypass the browser’s origin policy after the fact.
requestVideoFrameCallbackis undefined: feature-detect it and use a fallback only if its timing behavior meets your needs. The callback API is not available in all older browser environments.drawImage()rejects or draws nothing: verify the video has decoded usable current data, not merely that a source URL was assigned. A failed network request, unsupported codec, or unready frame must be fixed before drawing.
Or skip the browser setup
If what you need is a screenshot of the webpage containing a video—not a frame at a chosen playback time—ScreenshotNeo can capture the page through a single request. It does not replace seeking an HTML video element to extract a particular frame. Its website screenshot API removes cookie banners, newsletter popups, and chat widgets before capture; failed loads, bot checks, blank pages, and cache hits are not billed. It also provides an MCP server so AI agents can request screenshots.
cURL example (see the ScreenshotNeo API documentation):
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Frequently Asked Questions
Can I capture a frame from a video before it plays?
Yes, once the browser has loaded and decoded current frame data. Wait for media readiness rather than assuming that assigning a source URL makes a drawable frame immediately available.
Does requestVideoFrameCallback work in every browser?
No. MDN identifies it as Baseline 2024 for latest devices and browser versions since October 2024, but older versions and devices may not support it; feature-detect before use.
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