AVI: how Frame Witness recovers it

How it is found

AVI is a RIFF file: a header with the declared size, a list of streams and the movie data, often followed by an idx1 index and, for files over 1 GB, AVIX extensions. Frame Witness checks that structure within bounded limits and never decodes or invents bytes to make it fit.

Fragmented AVI

When an AVI was stored in pieces, its idx1 index gives the position of every chunk. Frame Witness uses it to place the pieces and labels the result as a hypothesis whose joins have not been proven unique.

Measured on generated videos

Both generated AVI videos on the formats test image came back with identical SHA-256 in Frame Witness. The image holds one short generated video per format, stored contiguously among zero-filled space and decoys, with no file system. It shows that the format is found and walked to its exact end; it does not show how often real cards keep these videos in one piece.

What cannot come back

• Overwritten data. Bytes that new files replaced are gone for every program.
• Full and overwrite formats. A full format in Windows writes zeros over the volume; an overwrite format or a wipe does the same with other patterns.
• SSD TRIM. A drive that receives TRIM usually erases freed blocks itself.
• Encryption without the key. A BitLocker volume, or a phone with file-based encryption, cannot be read without its key.

Try it on your own source

Download Frame Witness for Windows (version 1.0.14, Authenticode-signed by Aurelio Avila, SHA-256 fa22d6c7f97da0b4e5efa889e5abb9e4d98815a9b76ac0087424944b21bad6c2). The free account gives a quick scan of the first 8 GiB, up to 100 results, previews and saving files up to 1 MiB each; full scans and larger files need a licence, with current prices on the pricing page.

Related

• Formats Frame Witness recovers
• Test results and how they were measured
• Recover overwritten or interrupted video on a card or dashcam