What does the clip fingerprint tool do?
It reads a video file on your device and computes its SHA-256 fingerprint: a 64-character code that changes completely if a single byte of the file changes. It then helps you keep a custody sheet: who released the clip, who received it, when, and whether the fingerprint still matched.
The file is never uploaded. If you ask for the report, only its name, size, date and fingerprint are sent to our server with the request and kept for up to 45 days.
Why fingerprint a clip?
A crash clip from the recorder is copied many times: to a laptop, to storage, to an insurer, to a lawyer. Each copy should be the same file. Comparing fingerprints answers that in seconds, without watching the clip again.
Inputs you need
| Input | Where to find it | Tip |
|---|---|---|
| Clip file | The file exported from the recorder or the platform | Use the file exactly as exported. |
| Earlier fingerprint | The previous custody sheet | Paste it to compare. Spaces are ignored. |
| Recorder clock offset | Recorder screen next to GPS time or a synced phone | Write the sign: positive if the recorder is ahead. |
| Handovers | The people and places that held the clip | One row each, in time order. |
How it is calculated
SHA-256 is the hash function of the Secure Hash Standard, FIPS 180-4, published by NIST. Files up to 512 MB are hashed by the browser's own WebCrypto function. Larger files are read in 8 MB slices and hashed by the page itself, so the whole file never has to sit in memory. Both give the same result. The page code is tested against the published FIPS 180-4 example values.
Sources (read 2026-10-31): NIST FIPS 180-4 · MDN SubtleCrypto.digest()
Worked example
Type abc in the text field. The fingerprint is ba7816bf 8f01cfea 414140de 5dae2223 b00361a3 96177a9c b410ff61 f20015ad, the value printed in the FIPS 180-4 examples. Type abd and almost every character changes.
In the custody sheet, the recorder shows 07:42:10 and runs 28 s ahead of GPS time. The clip really started at 07:41:42 and, at 45 s long, ended at 07:42:27.
Reading the results
- Matches: the copy is bit-for-bit the file that was fingerprinted earlier.
- Does not match: the bytes differ. Find out why before you use the copy.
- Chain break: the person who released the clip is not the one who received it last.
- Not checked: the fingerprint was not re-computed at that handover.
Assumptions and limits
A fingerprint shows that two files are identical. It does not show when the clip was recorded, whether it was edited before the first fingerprint, or that any court, insurer or authority will accept it. Very large files take time to read, and the browser must stay open. The custody sheet needs legal review before you rely on it.