Copying a card so you know the copy is good

The failure that has no warning

A card copies. Every file appears. The folder sizes match. Three weeks later you open shot 47 and the last four seconds are green blocks, or the file will not open at all.

A plain drag-and-drop copy does not verify anything. The operating system writes bytes and reports success; it does not read them back. Most of the time this is fine. Occasionally a cable, a card reader, a failing card or a full disk produces a file that exists at the right size and contains the wrong bytes. You find out when you need it.

The fix is a checksum: compute a fingerprint of the source file, compute one of the copy, compare. If they match, the copy is byte-identical. This is what every broadcast and film production does at the card, and it takes one extra command.

Doing it free, on any machine

On macOS or Linux, rsync will copy and verify in one step:

rsync -aH --checksum --progress \
  /Volumes/CARD_01/ ~/Projects/2026-03-12_ClinicFilm/01_footage/CARD_01/

--checksum makes rsync compare file contents rather than size and timestamp. It is slower, and slow is the point.

To produce a record you can check later, write a manifest:

cd ~/Projects/2026-03-12_ClinicFilm/01_footage/CARD_01
find . -type f -exec shasum -a 256 {} \; > ../CARD_01.sha256

And months later, verify the whole folder against it:

shasum -a 256 -c CARD_01.sha256

Every file prints OK or FAILED. On Windows, certutil -hashfile <file> SHA256 does one file, and PowerShell's Get-FileHash handles folders in a loop. TeraCopy is free for personal use and verifies copies with a checkbox.

Dedicated offload tools exist — Hedge, Silverstack, ShotPut Pro — and are worth their money on a production with a runner doing this all day. For one person with a laptop, rsync --checksum does the same job for nothing.

Copy the whole card structure, not just the clips

Dig into a card and it is tempting to grab only the .MP4 files. Do not.

Many cameras store metadata, audio, spanned-clip indexes and colour information in sibling folders. AVCHD splits long recordings across multiple files that only reassemble via a playlist file. Sony's XAVC, Canon's structure and Panasonic's all carry sidecar data. Copy the entire card, folder structure intact, and keep it as an untouched original. Then work from a copy of that.

Name the folder for the card and the day: 2026-03-12_CARD_01_A7III. Never reuse a card name within a project, even across days, because two folders called CARD_01 will end up merged by somebody eventually.

Two copies before the card is formatted

The rule everybody agrees on and half of people break under time pressure: the card is not formatted until the material exists in two places on two different devices.

A working drive plus a laptop's internal disk counts. A working drive plus the same drive's second partition does not — one drive failure takes both.

If you can afford the cards, keep them unformatted until the project delivers. It is the cheapest insurance in this course, and the only one that protects you from the mistake where somebody deletes the wrong folder.

A log for the shoot

A plain text file in 06_docs that lists, per card: date, camera, what is on it, the checksum manifest filename, where the two copies live, and whether the card has been formatted. It takes two minutes at the end of a shoot day and it is the document that answers, in March, the question of whether the missing interview was ever copied at all.

Where this is genuinely overkill

If you filmed a two-minute vertical video on your phone and it is already in your phone's cloud backup, do not build a manifest for it. Checksums earn their cost when the material is irreplaceable and large: an event that happened once, an interview with somebody who has now moved country, a client shoot you cannot repeat.

The honest test is the one question: if this folder were gone tomorrow, could it be re-shot? If yes, copy it normally. If no, verify it.

Today

Take the most irreplaceable folder of footage you own, generate a SHA-256 manifest for it, and store the manifest somewhere separate from the footage. You have just made every future copy of that folder checkable.