A proxy file is a smaller, lower-resolution copy of a video — sometimes an image — generated automatically so that an app can scrub, preview and search a library without decoding the full original every time. The original stays untouched on disk; the proxy is a disposable convenience file that can always be rebuilt from it.
Why video needs this and a JPEG usually doesn't
A clip shot at a high resolution can be gigabytes on disk, and decoding that much data just to draw a thumbnail or scrub through a timeline would make a library feel sluggish the moment it holds more than a handful of clips. A proxy solves that by trading resolution for speed: a much smaller file that is still enough to search by, preview and drop onto a board, while the full file waits untouched for whenever the real resolution is actually needed.
Stills mostly skip this problem — a JPEG or PNG is already small enough that a thumbnail is nearly free to generate — which is why "proxy" comes up almost entirely in the video half of a reference library.
~/Movies/Reference- Fight choreography
- Lighting studies
- coii-thumbnailswritten by Coii Ref
- coii-proxieswritten by Coii Ref
- coii.dbwritten by Coii Ref
Where the proxy actually lives
This is the detail worth checking before trusting a tool with a video-heavy library: does the proxy live inside your folder, or inside the app's own managed storage somewhere else on disk? Coii Ref writes proxies, thumbnails and its search database into the same folder you pointed it at, at the resolution the canvas actually needs — so a canvas full of footage scrolls as smoothly as a canvas full of stills, and backing up that one folder backs up the proxies along with everything else. What actually happens to a library if the app behind it goes quiet covers the same folder-first argument from the angle of what happens years later rather than what happens on import.
What a proxy is not
A proxy is not a backup, and it is not a substitute for the original in any context that matters — export, print, or handing the file to someone else. It exists purely so the app looking at your library does not have to decode the master file every time it draws a frame. Losing a proxy loses nothing: regenerating it is a re-scan, not a recovery.
It is also not the same thing as a sidecar file. A sidecar carries metadata that a format can't hold itself; a proxy carries pixels, at a size chosen for speed rather than fidelity, and the two solve unrelated problems that happen to both live next to the file they describe.
The comparison worth checking
refern also builds proxies for video review, covered in the full comparison between it and Coii Ref — both apps take video seriously rather than treating it as an afterthought to images, and the proxy is the part of that work a reader never sees directly but would notice the absence of on a large library.