.AVIF file signature
A AV1 Image File Format file begins with the bytes 66 74 79 70 61 76 69 66 (ftypavif in ASCII) at offset 4 (0x4). The signature is the same whatever the file is named, which is why a renamed or extensionless AVIF file is still recognisable.
Signature
| Offset | Hex | ASCII |
|---|---|---|
| 4 | 66 74 79 70 61 76 69 66ISO base media container; ftypavis for image sequences. | ftypavif |
MIME type: image/avif · usual extensions: .avif
How to check a file's signature
Without installing anything: drop the file on our detector. It reads the bytes in your browser and shows the hex dump alongside the verdict; nothing is uploaded.
macOS and Linux (Terminal):
xxd -l 32 file.avif
file file.avifWindows (PowerShell):
Format-Hex -Path file.avif -Count 32This signature sits at offset 4, so look there rather than at the first bytes: xxd -s 4 -l 16 file.avif.
If the bytes do not match
A file named .avif whose first bytes are something else is not a AVIF file. The common explanations are a wrong or deliberately misleading extension, a download that saved an HTML error page instead of the file, or a container such as ZIP wrapping the real content. The detector reports what the bytes say; the AVIF guide explains what a genuine file should contain.