How the resolution is measured
A page can't switch a camera to an exact size, only ask for one. The test asks for the size you choose as an ideal, and the camera answers with the nearest mode it has. Then it reads back what it actually got in two places: the track's settings, which say what the camera was configured to deliver, and the size of the picture in the video element, which is what you see and what a snapshot saves. Normally the two agree; when they don't, the page says so, because browsers can rotate a phone's picture or rescale a stream.
Auto asks for 1280 × 720, the size video calls use. Leave it out and most browsers open a camera at 640 × 480 whatever it can do, which is why a camera can look much softer on a page that never asked for more. The other presets ask for 480p up to 4K. Find maximum resolution goes further: it asks the running camera for each size in turn, from 4K down, and records what it switched to for each. A size counts as honored when the camera delivers at least that many pixels in both directions. When it is done the camera goes back to the size you had chosen.
How the frame rate is measured
Browsers can tell a page when each video frame is shown (requestVideoFrameCallback). The test records a timestamp for every frame, preferring the time the camera captured it, then the browser's media timestamp, and only as a last resort the time it was due on screen. Those times come from the camera side, not from how fast this page redraws, so the result is the camera's rate and not the screen's.
The rate comes from the median gap between frames, so a few late frames don't drag it down: a gap of 33.3 ms is 30 frames a second. A gap of about twice the median means a frame never arrived and counts as one dropped frame; three times as long counts as two. Jitter is the spread of the gaps that weren't drops, in milliseconds, and the histogram shows every gap: a tall bar at the normal interval and a small one at double it is a steady camera that lost a few frames. The report needs about 3 seconds of frames, and it starts over when the picture changes size, since the frame rate often changes with it.
When the page is busy the browser may skip a frame callback while the frame is still shown. The test notices this from the count of frames the browser reports it presented, and shows it as late callbacks, not as dropped frames. A hidden tab pauses the count altogether, and the time it was hidden is left out rather than read as missing frames. Browsers that can't time frames show the frame rate the camera is set to, which is what it was asked for and not a measurement.
Why a camera can deliver less than you ask for
Every camera has a short list of modes, each a size at a frame rate, and asking for something between them gets the nearest one. Beyond that, several things hold a camera below what is printed on its box:
- Bandwidth. Uncompressed 1080p video at 30 frames a second is roughly a gigabit per second, more than a USB 2.0 port carries. Cameras compress inside the camera to fit, and a hub, an extension cable or other busy devices on the same port can leave too little room for the larger modes. A direct USB 3 port avoids most of it.
- Light. At 30 frames a second a frame can expose for at most a thirtieth of a second. In a dim room many cameras switch to a slower mode, 15 or even 7.5 frames a second, to gather more light, so a camera that measures 30 in daylight can measure half that at night. Below about 24 frames a second motion looks choppy.
- The request. Browsers open a camera at 640 × 480 unless asked for more, and a page that asks for a size the camera doesn't have gets the nearest one.
- Other software. An app that already holds the camera may have opened it at a lower size, and a video-call app can lower the quality it asks for when the network is slow.
- The label. Some cameras sold as 2K or 4K produce that picture by scaling up a smaller sensor's image. The test reports what the camera delivers, not how much detail the sensor captured.
What the camera controls are
Where the browser supports it, the test lists what the camera says it can do: the ranges of width, height and frame rate, and the controls for zoom, focus, exposure, white balance and the torch, the light some phone cameras have. The list comes from the camera and your system, so the same camera can show different things on different computers and in different browsers. Chrome reports the most. Some browsers, older Firefox versions among them, don't provide the list at all, and the test says so instead of leaving a blank. These are ranges the camera reports, not controls this page changes.
Your video stays on this device
Nothing leaves your browser. The picture is drawn and measured on your device and isn't recorded or uploaded. A snapshot is made in the tab from the frame on screen, kept in memory and offered as a download; it's written to your disk only if you save it. Stopping the camera, switching to another one, or leaving the page, including by following a link to another test, turns the camera off and its indicator light goes out.
Questions
Why isn't my webcam detected?
Start with the basics: check the camera is plugged in firmly, and that a laptop's camera isn't switched off by a function key or a sliding shutter. Then check that your system sees it: on a Mac, another app such as Photo Booth should show it; on Windows, look under Cameras or Imaging devices in Device Manager. On Windows, switching off camera access in Settings, Privacy & security, Camera hides every camera from browsers, and so does a company policy on a work computer. If the test finds a camera but shows only black, look for a lens cover or privacy shutter. Try another USB port, and if the camera is on a hub, plug it into the computer directly.
Why does the test say my camera is in use, or fail to start it?
Many cameras can serve only one app at a time, and Windows is the strictest about it. Close video calls (Zoom, Teams, Meet, FaceTime or Discord), recording and streaming software such as OBS, the Camera app, and any other browser tab that has the camera open, including this page in a second tab. If nothing else seems to be using it, quit and reopen the browser, unplug the camera and plug it back in, or restart the computer. A camera the system itself has blocked for the browser reports the same kind of failure, so also check the privacy settings for your browser.
Why is my webcam only 30 frames per second?
Thirty is what nearly every webcam is built for. Each frame needs light, so at 30 frames a second the camera can expose for at most a thirtieth of a second, and sixty would halve the light on every frame. Higher rates also need much more data than the cable and the video compression can carry at full size, so cameras usually offer 60 only at 1080p or lower, and 4K at 30 or less. Video calls send 30 or less anyway. If the test measures less than 30, the usual cause is dim light: many cameras drop to 15 or even 7 frames a second to expose longer. Turn on a light in front of you and press Measure again.
Why is the image mirrored?
A mirrored preview looks the way you expect from a mirror: move your hand to the right and your image moves to the right. It is only how the preview is drawn. Other people on a call see the true image, with text and left and right the way they really are, and the snapshot this test saves isn't mirrored either. Choose As captured under Preview to see what they see. The back camera on a phone is never mirrored.
How do I check my webcam quality before a video call?
Start the camera at the resolution your call app uses, usually 720p, and look at what is delivered rather than what the box says. Check the delivered size is what you asked for, and the measured frame rate is close to 30 with few or no dropped frames. Sit where you will sit for the call: a face lit from the front gives a sharper, faster picture than one lit from behind, and light is the biggest single factor. Take a snapshot and look at it at full size for noise, blur and colour. Use Find maximum resolution to learn what the camera can do, then close other apps that use the camera before the call.
How do I reset my browser’s camera permission?
In Chrome or Edge, click the site controls icon at the left end of the address bar, set Camera to Allow (or reset the permission) and reload the page. In Firefox, click the crossed-out camera icon in the address bar, remove the blocked permission and press Start camera again. In Safari on a Mac, choose Safari, Settings, Websites, Camera and set this site to Allow. On an iPhone or iPad, tap the page menu in the address bar, then Website Settings, Camera. If the browser is allowed but the camera still fails, your system may be blocking the browser: on a Mac, check System Settings, Privacy & Security, Camera; on Windows, check Settings, Privacy & security, Camera.
Why does the camera deliver less than I asked for?
The test asks for a size as an ideal, and the camera answers with the nearest mode it has, so a difference is the camera’s or the connection’s doing. Common causes are a USB 2.0 port, hub or long cable that cannot carry a big picture, dim light that makes the camera switch to a smaller or slower mode, another app already holding the camera at a lower size, and a camera that simply tops out lower than its box suggests. Plug it directly into a USB 3 port, add light, close other camera apps, and use Find maximum resolution to see which sizes it actually honors.
Is my video uploaded or saved anywhere?
No. The camera picture is shown and measured by your browser on your device, and nothing is sent to a server. A snapshot exists only in this tab until you save it to your own disk, replace it or leave the page. Stopping the camera, switching to another one or leaving the page turns the camera off, and the camera's indicator light goes out with it.