Webcam Test

Reading the numbers

Resolution is the size of each frame in pixels, width by height. 1280×720 is 720p, about 0.9 megapixels; 1920×1080 is 1080p, about 2.1 megapixels; 3840×2160 is 4K, about 8.3 megapixels. The figure shown is read from the video itself while it plays, so it is what the camera is delivering right now rather than the number printed on the box.

Browsers open a camera at 640×480 unless the page asks for more, which is why some webcam tests tell owners of HD cameras that they have a VGA one. This test asks for 1080p by default and reports what came back. Ask for 4K and receive 1280×720, and 720p is the camera's real ceiling — or the most it will deliver over this connection. Largest mode shows the biggest size the camera reports, where the browser exposes it: Chrome and Edge do, Firefox and Safari do not.

Frame rate appears twice. Camera setting is the rate the camera was configured for; measured frame rate counts the frames that actually reach the page each second. When they disagree, believe the measured one — it is what the person on the other end of a call will get.

Aspect ratio follows from the resolution: 16:9 for widescreen modes such as 1280×720, 4:3 for older ones such as 640×480. A 4:3 picture in a 16:9 meeting window is either cropped or shown with bars at the sides.

Why the frame rate drops

Light is the usual reason. A camera that cannot gather enough light in a thirtieth of a second lengthens each exposure, and a frame that takes a fifteenth of a second to expose means fifteen frames per second. Laptop webcams in a dim room commonly fall to half their rated rate, and the picture turns grainy at the same time. A lamp in front of you — not behind you — usually restores both.

Bandwidth is the other. Uncompressed 1080p at 30 frames per second is roughly 124 MB every second (1,920 × 1,080 pixels × 2 bytes × 30), more than a USB 2.0 port can carry, so webcams compress each frame — usually as MJPEG — to deliver high resolutions. Through a hub, a long extension cable or a crowded USB controller, a camera can fall back to a lower rate or a smaller size. Plug it straight into the computer and close other video software.

A heavily loaded computer shows up here too. The measured rate counts frames the browser actually presents, so a processor busy with other work can lose frames that the camera did send.

When the camera will not start

Blocked for this site: the browser remembers a refusal. In Chrome and Edge, click the icon at the left of the address bar and set Camera to Allow, or remove the site from chrome://settings/content/camera. In Firefox, click the crossed-out camera icon in the address bar, clear the block and reload. In Safari, choose Safari → Settings for This Website → Camera. When the widget detects a block, it shows the steps for the browser you are using.

Blocked by the operating system: this overrides every browser setting. On Windows 11, open Settings → Privacy & security → Camera and make sure Camera access, Let apps access your camera and Let desktop apps access your camera are all on — browsers count as desktop apps. On macOS, open System Settings → Privacy & Security → Camera, switch your browser on, then quit and reopen it. Chrome reports this case as "Permission denied by system".

In use by another program: Chrome's "NotReadableError: Could not start video source" nearly always means another application has the camera open — Zoom, Teams, Skype, OBS, the Windows Camera app, or a call running in another tab. Close it and try again; on Windows, check the system tray for apps that keep running after their window closes.

Not found: the camera is unplugged, disabled in the system's device settings, or switched off by a function key on some laptops. A physical privacy shutter is different — the camera still starts, and you get a black picture rather than an error.

The mirrored preview, and what others see

The preview is mirrored by default, because that is how a mirror behaves and how video-call apps show you to yourself: raise your right hand and the hand on the right of the screen moves. The people you call see the unmirrored picture, which is why the writing on a T-shirt looks backwards to you and reads correctly to them.

Switch mirroring off to see the camera's true orientation. The snapshot is saved exactly as the preview shows it, so turn mirroring off before taking one if orientation matters — a photo of a document or a badge, for instance.

What happens to the video

The picture goes from the camera to this tab and nowhere else. Nothing is recorded or stored, and the page sends no video anywhere; a snapshot exists only when you press the button and is saved directly to your device. Pressing Stop ends the camera's track, which is what turns its light off. If the light stays on after Stop, another tab or application is using the camera.

Camera names appear only after you allow access: browsers withhold device names from sites without permission, because a list of someone's hardware helps identify them.