everyday mac tools

Video editing caches and scratch files filling a Mac

· 7 min read

An editing project that looks like 40 GB of footage can easily be using 300 GB of disk. The difference is render files, proxies, previews, autosave versions and old exports, most of which the editor can rebuild and none of which it deletes on its own.

The job is not to delete everything with the word cache in its name. It is to separate what regenerates (safe, costs you time) from what is the only copy of something (not safe at all).

Where the space actually goes

Six categories account for nearly all of it.

Render and preview files. Every time the timeline plays back smoothly after an effect, something was written to disk. These rebuild on the next playback, so deleting them costs render time, not work.

Proxy and optimized media. Lower resolution copies of your footage, made so editing feels responsive. They regenerate from the originals, as long as the originals still exist. If you ever deleted camera files because “the project still plays”, the proxies may be all you have left, and they are not a master.

Camera card copies. Whole card backups in a project folder, often twice: one from the import, one from the manual copy you made because you did not trust it. Irreplaceable, and not something to keep on the internal drive.

Autosave and version history. Some editors keep every autosave for months, and thousands of copies of a project file add up in a folder nobody looks at.

Exports. The 12 GB master, the 3 GB review copy and the six attempts before the one you sent. Old exports are usually the single biggest win, because nothing regenerates them and nothing needs them once the final is delivered.

App caches outside the project. Thumbnails, waveform caches and analysis data live under ~/Library/Caches and in each app’s container, far from the project folder you were inspecting.

Finding it before you delete anything

Start with the Mac’s own view: System Settings > General > Storage. The bar chart is coarse, and System Data is where most editing leftovers get filed, which is why the picture never adds up. What System Data is on a Mac and how to shrink it explains what sits inside that block.

For a project folder, Finder is enough. Open the folder, switch to list view, and press Command-J to turn on Calculate all sizes. Sort by size and the render or proxy folder usually announces itself immediately.

Terminal gives you the same answer faster on a big tree, and it only reads sizes, so it changes nothing:

du -sh ~/Movies/* | sort -h

To find old exports scattered around, search by kind and size rather than by name. In a Finder search window, set the criteria to Kind is Movie and add File Size is greater than 1 GB. Find the largest files on a Mac covers the rest of that technique.

Clearing the safe things first

Work in this order, from lowest risk to highest.

  1. Use the editor’s own command. Most editing apps have a menu item that deletes render files, generated proxies or optimized media. Use it in preference to dragging folders to the Trash, because the app updates its own database at the same time.
  2. Clear exports you have delivered. Keep the final master and the project file; the earlier attempts are not coming back into use.
  3. Empty old autosaves. Most editors let you cap how many versions to keep. Set it, then delete the rest.
  4. Look at app caches last. These regenerate, but deleting the wrong one costs an app twenty minutes rebuilding waveforms. Which caches are safe to delete on a Mac draws the line.
  5. Empty the Trash. Nothing is freed until you do, and a full Trash is the most common reason the bar chart does not move.

Then check what quietly holds space after a cleanup. Time Machine keeps local snapshots on the internal drive, which can pin deleted files for days, and macOS reports that as purgeable rather than free. Time Machine local snapshots taking space on the internal drive covers what to do about it.

What not to delete

  • Original camera files, even when proxies exist. Verify the originals are on two drives before touching anything in the project folder.
  • Anything inside an editor’s library or package by hand. Pruning folders through Show Package Contents is how projects get broken. Use the app’s own media management instead.
  • A folder you cannot identify. Move it to an external drive for a week rather than deleting it. If nothing complains, it goes.
  • Audio peak or analysis files for a project still in progress. They regenerate, but at the worst possible moment.

Getting the whole picture in one pass

Doing this by hand once is fine. Doing it every month, on a Mac that also holds a forgotten iOS backup and a pile of build artifacts, is where it gets tedious.

Crumb audits the whole Mac rather than just your home folder, and the audit is read-only: it breaks System Data into its parts (caches, logs, swap, temporary files, leftovers), shows Time Machine local snapshots and iOS backups, and on a shared Mac shows which account is using the space. Reclaimable items are grouped by category with the total shown before you commit.

The feature that fits this problem best is Ask Crumb: point it at a folder you do not recognize and it explains what the item is, whether it regenerates and what breaks if it is gone, then proposes a plan. Nothing is deleted until you approve the plan, and reclaimable removals can be reviewed and undone afterwards.

The whole-Mac audit, the System Data breakdown and one full cleanup are free forever; unlocking everything else is $9 once for up to 2 Macs, with no subscription. It does not repair disks or recover deleted files, so the rule about verifying your originals still stands.

Keeping it from coming back

  • Put scratch, render and proxy locations on an external drive in the editor’s preferences. Those files are meant to be disposable, and external storage is cheaper per gigabyte.
  • Archive a project when it is delivered: originals plus project file plus final master, to two places, and delete the generated media.
  • Keep the internal drive under roughly 85 percent full. Editing writes constantly, and a nearly full drive turns into swap pressure and beachballs during playback.

If the space keeps vanishing even after a cleanup, your Mac fills up again a week after you cleared it works through the usual suspects.

Questions

Will deleting render files lose any of my edit? No. Render files are the result of your edit, not the edit itself: the timeline, the cuts and the settings live in the project file. You pay in render time the next time you play that section.

My project still plays after I deleted the originals. Am I fine? No. It is playing from proxies, which are lower quality copies made for editing, and an export from those will not match a master. Recover the originals from a backup.

Why is the disk still full after I emptied the Trash? Local snapshots and purgeable space both hold on to recently deleted data. See purgeable space on a Mac and why it will not free up.