A webcam's advertised resolution is what it can be asked for. What arrives depends on the mode the browser gets, the light, the USB link, and the processor encoding the call.
- The webcam resolution test asks for each standard mode the camera claims, reads back the size the browser reports, and counts the frames that actually arrive.
- A call app sends less than the camera gives when its encoder runs short of processor time, and the browser's WebRTC statistics say when that happened.
- The test sends the camera through a call inside the page, with no server, so you see what a call on this computer would send.
The short answer
Ask the camera for a mode, then count. The size the browser reports after the request shows whether you got the size you asked for, and the frames counted per second show whether you got the rate. Then send it through a call: what is encoded and sent is what the other side sees.
We have no recorded runs of this test in our validation notes yet, so this guide quotes no measured results. Every line and constant below is the one the test's code applies.
Which modes are tried
The test tries 480p (640 by 480), 720p (1280 by 720), 1080p (1920 by 1080), 1440p (2560 by 1440) and 4K (3840 by 2160), each at 15, 30 and 60 fps: 15 modes, less those outside the ranges the camera states. Each is held for 2 seconds while frames are counted.
A mode is delivered when the size matches and the counted rate is within 10% of the rate asked for, so a 30 fps mode counted at 27 fps or more is delivered. The 10% is our line. A mode that came back smaller is marked smaller; one that arrived slower is marked slower.
Why a camera sends less
- Light. Many cameras lengthen the exposure in a dim room, which lowers the frame rate. Add light facing you and try again.
- The link. A slow USB port or a shared hub can limit the larger modes.
- The browser or the camera may scale a mode it cannot serve to one it can, and report the smaller size.
- In a call, the encoder. When the processor cannot keep up, the browser lowers the call's resolution or rate.
What the call shows
The page connects two WebRTC peers to each other and reads the sender's statistics: the codec, the encoder's name where the browser shares it, the time spent encoding each frame, the size and rate sent, camera frames the encoder skipped, and the reason quality was limited. A limit that held for more than 10% of the window, our line, is reported as the limit.
Limited by cpu means the processor could not keep up, and a call app on this machine will do the same. Limited by bandwidth, here, is the browser's estimate still climbing at the start of a call, because the call never leaves the computer. It is not your connection.
Terms used here
Questions
- Why does my 1080p webcam look soft in calls?
- Call apps often send less than the camera's size, starting small and stepping up as the connection allows, and lower it again when the processor is short. The call section of the test shows what this computer would send and why.
- Does the test record or upload video?
- No. The call runs between two connections inside the page and nothing leaves it.