MP3 file signature
Magic number at the start of the file · ID3
Most MP3 files start with an ID3v2 tag, the ASCII text ID3, holding title and artist metadata. A tagless MP3 instead starts at an MPEG audio frame, whose sync word begins FF followed by Fx.
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 49 44 33 (the text ID3), it is a MP3 file.
Signature variants
MP3 appears with more than one byte pattern. These all identify the same family:
| Hex signature | Offset | Note |
|---|---|---|
| 49 44 33 | 0 | ID3v2 metadata tag at the start |
| FF FB | 0 | raw MPEG-1 Layer III frame, no tag |
| FF F3 | 0 | MPEG-2 Layer III frame |
Formats that use the 49 44 33 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.mp3
- hexdump -C -n 16 example.mp3
- file example.mp3
Windows (PowerShell)
- Format-Hex -Path example.mp3 -Count 16
Python
- open("example.mp3","rb").read(3).hex()
In your browser
- Drop the file into the WhatFileType identifier, which reads the signature without uploading it.
Frequently asked questions
What is the MP3 file signature?
MP3 files start with the hex bytes 49 44 33 (ID3 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.mp3 on Linux or macOS, or Format-Hex -Path example.mp3 -Count 16 in Windows PowerShell, and read the first bytes.
Can a file fake the MP3 signature?
Renaming a file does not change its bytes, so the extension can lie but the signature usually cannot. A genuine MP3 file has these exact bytes; a file with the wrong bytes is not really MP3, whatever its name says.