Checksum mismatch
Also known as: hash mismatch, verification failure
A copied file whose computed fingerprint differs from the original, which proves the copy is damaged before anybody opens it.
Updated
What it means
A checksum reduces a file to a short value. Compute it on both copies, compare, and an exact match means every byte arrived; a mismatch means at least one of them did not.
It is the only honest verification. A copy that reported success can still be wrong, which is what File corruption looks like from the outside rather than from looking at the picture.
The value says nothing about where the damage is. A mismatch means the copy is untrustworthy, not that a particular frame is broken, which is why it leads to a recopy rather than to an attempted repair.
How it works in practice
Verification belongs in the offload. A copy tool that hashes both sides as it goes catches a bad transfer while the card is still in the reader, which is the only moment a recopy is free.
The card is the only copy until it passes. Card formatting after an unverified copy is how sessions get lost, and the discipline is to verify first and format second.
It also catches slow decay. Re-hashing an archive on a NAS occasionally reveals a file that changed on disk without anybody touching it, because disks do that quietly.
What to watch out for
A mismatch is frequently read as a false alarm. It is not; the usual cause is a failing cable, a failing drive or a card on its way out, and all three get worse rather than better.
Verifying nothing is the common state. Most copies are never checked, which means Corrupted frames get discovered during an edit rather than during an offload.
It does not help after the fact. A file that was already damaged when it was written produces a matching hash on both sides, which is a Video file repair problem instead.
How RawClip handles it
Uploads are verified on arrival, so a file damaged in transit is detected rather than analysed. A clip that was already damaged on the card is a different matter: the readable part is used and the rest of it is skipped.