Proxy file

A proxy file is a lightweight, lower-resolution stand-in for a heavy original clip, used so an editor can cut smoothly on hardware that could never play the source in real time. Modern cameras produce footage at bitrates that strain most laptops: 4K H.264 around 100 Mbps, 6K Blackmagic RAW in the hundreds of Mbps, 8K R3D at gigabit speeds. Editing natively on those files leads to dropped frames, laggy scrubbing and long renders. A proxy is a smaller alternative, usually H.264 or ProRes Proxy at 720p or 1080p, that behaves identically in the timeline but weighs ten to fifty times less.

The key idea is that a proxy carries the same timecode, frame rate, duration and file name relationship as its original, so the NLE can swap one for the other without changing a single edit. You cut, trim, add effects and build the whole sequence on the proxies, then at the end the software re-links each clip to its full-resolution source for the final render. Every edit you made on the proxy applies to the original automatically.

All four major NLEs support this natively but handle it differently. Premiere Pro attaches a proxy to each clip and toggles between proxy and full resolution with a single button, exporting from the originals. DaVinci Resolve, Final Cut Pro and Avid use their own proxy or optimized-media systems and relink to the originals at the finish. Because the mechanism is per clip, you can mix proxied and full-resolution clips in the same timeline.

Proxies are not a quality compromise in the final product, because the export always comes from the originals; they only trade resolution during the edit for speed. The one cost is disk space, since a proxy sits alongside the original. That is the problem Sanbila targets: it generates the proxies in the cloud and keeps the heavy originals there too, so your SSD holds only the light proxies while you cut, and the originals stream back at export.