How Preen's camera preview actually works, and where it stops

You have ninety seconds before a call starts, and you want to know what the room is about to see: which camera answered, whether the frame is level, whether your face is actually in it. Preen is a menu bar app that opens a live camera preview in a click, lets you switch between whatever cameras macOS can see, and keeps that view open in a small floating window while you move to your meeting app. It needs a recent macOS, listed on the app page, and it never asks for camera access until you tell it to.

I build Preen. Every fact about the app traces to its own source code or to Apple's published documentation, checked on 23 July 2026.

Why the moment before the mirror matters more than the mirror itself

Every Mac already has a way to see its own camera. Photo Booth opens one. So does FaceTime. The trouble people actually run into is timing: you do not want a full app opening a window, requesting focus, and possibly grabbing the camera for the rest of the call, ten seconds before you need to join something else entirely. Preen is built around one job, staying out of the way until the moment you need to glance at yourself, then getting out of the way again the instant you do not.

That framing matters because it explains a design choice that trips a few people up. Preen does not take exclusive ownership of your camera the way a recording app might. It builds a plain input on a capture session and nothing more, so it never locks the device, never adjusts exposure or frame rate, and cannot free a camera that some other app is already holding onto.

Check what your own setup actually shows before a call, not after.

The trial runs every feature Preen has, snapshot capture and the floating window included, so nothing is held back while you find out whether it fits how you work.

One session, and a single rule for when the light comes on

Preen owns exactly one capture session for the entire time it runs, and every window you open, the small popover or the floating mirror, draws from that same session rather than opening a second one. The rule that decides whether your camera is actually running is a single check: the session starts the moment either the popover or the floating window is visible, and stops the moment both are closed. Close the popover while the floating window stays open, and the camera keeps running, because the rule only asks whether anything is currently watching, not which window is doing the watching.

Access itself follows the same restraint. Preen never requests camera permission on launch or on first open. It only checks your existing authorization status, and the one place that can trigger the actual system prompt is a button you press yourself, on a card that explains what the preview does before macOS ever asks.

Switching cameras rebuilds more than the picture

Preen groups the cameras it finds into built in, continuity, external, and desk view, in that order, and keeps the order stable across a hot plug so a picker does not reshuffle itself while you are looking at it. Switching between them removes the previous input and adds the new one inside a single configuration block, which is also why mirroring gets reapplied every time: the underlying connection is new even though the window looks the same. If a camera disconnects mid session, Preen notices through the same reconnect mechanism and falls back to your default camera rather than leaving you staring at a frozen frame.

None of this reaches into another app's territory. Where a call actually goes wrong is usually one level up, in whichever app is doing the calling, since macOS lets each app remember its own camera choice independently, and Preen's preview cannot change what Zoom or Teams decides on its own.

Two things worth knowing before you rely on it

The floating mirror does not remember where you left it. Every launch centers it fresh at the same fixed size, because there is no saved position behind it at all, so if you drag it to a corner today, it will be back in the middle tomorrow.

Flipping between mirrored and true view has a real gap, too. The toggle updates the popover and any photo you take immediately, but if the floating window is already open when you flip it, that window keeps showing the old orientation until you close and reopen it. It is a genuine inconsistency, not a rendering delay, and I have not fixed it yet.

Muting your microphone from Preen is worth a separate mention rather than an assumption. It changes a Core Audio device property directly, which is a different thing than a per app mute, and your meeting app can keep showing you as unmuted even while the system input is actually silent.

A snapshot is a PNG, a clipboard copy, and one filename you can lose

Pressing the shutter saves a PNG straight to your Pictures folder and copies the same image to your clipboard in one action, so pasting it somewhere else needs no extra step. The filename is built from the date and the minute, not the second, and there is no counter appended if two snapshots land in that same minute. The second one silently replaces the first, since the save itself does not check whether a file already exists at that path. Take two photos close together and only the second survives.

This will not fit everyone

If you need a floating preview that can sit pinned to a corner with adjustable opacity, or one you can trigger with a global keyboard shortcut, Preen has neither. Every action lives inside the menu bar panel, and the window itself is fixed in appearance by design.

If your workflow depends on freeing a camera that another app refuses to release, no preview tool including this one can do that for you, since macOS enforces exclusive access at the hardware level and nothing in a normal capture session carries the authority to override it. And if you are still on an Intel Mac, or need something for macOS 13 or earlier, Preen will not run at all. Five other ways to look at your camera before Preen even enters the picture are worth a look if any of that describes you.

Questions people ask

Does Preen turn my camera on the moment I open it?

Only if the popover or the floating window is visible and access is already authorized. It never starts the camera on launch, and it never requests permission without you pressing the button that asks for it.

Can Preen take over a camera another app is using?

No. It does not have, and does not want, an exclusive access API. If another app is holding the camera, Preen can only tell you the camera is busy, not force it free.

Does muting the microphone in Preen mute me in Zoom too?

It mutes the system input device directly, so most of what listens to that device goes quiet, but the meeting app's own mute indicator is a separate thing it draws itself, and it may not update to match.

Will the floating window remember its size and position?

No. It opens at a fixed size, centered, every single time, because nothing about its last position is saved anywhere.

Changelog: 22 July 2026, rewritten from a short product summary into a full explainer covering the capture session, the floating window, and where the app stops.