A black rectangle in Zoom is usually not “Zoom is down.” The camera is blocked, busy, or the wrong one is selected. Prove the hardware in a plain tab first. If it fails there, the meeting app cannot save you.
Prove it in a browser tab
Open the webcam test and microphone test. Click Start camera & microphone and allow the prompt.
- Preview works, meter moves → join the call. The path is fine.
- Preview is black, or the meter is dead → work the list below. The site is not the camera.
The usual pile
This site is blocked. Click the lock icon in the address bar. Set Camera and Microphone to Allow. Reload.
Another app still owns the device. Quit Zoom, Meet, Teams, Photo Booth, FaceTime, Slack huddles. One process at a time. On a Mac, a leftover meeting window is the classic thief.
The OS denied the browser.
- Mac: System Settings → Privacy & Security → Camera and Microphone. Chrome, Safari, Firefox, and Edge each need their own tick.
- Windows: Settings → Privacy & security → Camera / Microphone. Allow desktop apps, then allow that browser.
- iPhone: Settings → Safari (or Chrome) → Camera / Microphone.
- Android: Settings → Apps → the browser → Permissions.
Wrong device. Built-in camera vs USB cam. Built-in mic vs headset. Switch in the list on the test page. A live badge with a black frame often means the other camera.
Hardware off. Laptop shutter, Fn camera key, a mute LED on the webcam, a hardware mic switch on the headset.
Not HTTPS, or a picky extension. Camera access needs a secure context. Try a private window with extensions off if the prompt never appears.
Browser-specific nits
Chrome and Edge remember a block forever until you change the lock icon. Safari on macOS also needs the system privacy tick — the site prompt is not enough. Firefox has its own permissions panel behind the address-bar icon; it does not share Chrome’s allow list.
If the test works and the call does not
The meeting app picked a different camera or still holds a stale device. Switch devices inside Zoom / Meet / Teams, or quit that app and start it after the test page has released the stream (hit Stop).
The happy-path ritual is test your webcam and microphone before a call. If you are choosing a tester at all: is an online webcam test safe.