Core Audio Format file signature
Magic number at the start of the file · caff
Apple's Core Audio Format begins with the marker caff. Unlike WAV it has no 4 GB size limit and can wrap many codecs.
What this magic number means
A magic number is a short, fixed run of bytes at a known position that tells a program what a file really is, no matter what the filename says. If a file starts with the bytes 63 61 66 66 (the text caff), it is a Core Audio Format file.
Formats that use the 63 61 66 66 signature
These file types in our database carry this signature:
How to check a file's signature
You can read the first bytes of any file yourself. The magic bytes are shown in hex, the same way this page lists them.
Linux & macOS
- xxd -l 16 example.caf
- hexdump -C -n 16 example.caf
- file example.caf
Windows (PowerShell)
- Format-Hex -Path example.caf -Count 16
Python
- open("example.caf","rb").read(4).hex()
In your browser
- Drop the file into the WhatFileType identifier, which reads the signature without uploading it.
Frequently asked questions
What is the Core Audio Format file signature?
Core Audio Format files start with the hex bytes 63 61 66 66 (caff in ASCII). This magic number identifies the format regardless of the file's name or extension.
How do I check a file's magic number?
Open the file in a hex editor, or run a command such as xxd -l 16 example.caf on Linux or macOS, or Format-Hex -Path example.caf -Count 16 in Windows PowerShell, and read the first bytes.
Can a file fake the Core Audio Format signature?
Renaming a file does not change its bytes, so the extension can lie but the signature usually cannot. A genuine Core Audio Format file has these exact bytes; a file with the wrong bytes is not really Core Audio Format, whatever its name says.