MKV and WebM: how Frame Witness recovers them

How they are found

MKV and WebM are Matroska files that start with the EBML header (1A 45 DF A3). Frame Witness carves them only when the segment has a finite size it can walk to the end, without decoding or repair.

Fragmented files

Pieces of an MKV that end in the middle of a frame are followed through the Matroska structure (since 1.0.10). A file whose segment size was never written, as in a live stream that was cut, is kept as found.

Measured on generated videos

Both generated MKV and WebM 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