Skip to content

M4B (.m4b)

.m4b file signature | audio/mp4

Safe

Magic Bytes

Offset 4
66 74 79 70 4D 34 41 20

Sources: Apache Tika

All Known Signatures

4 signature variants are documented for .m4b files across multiple sources.

Hex Signature Offset Sources
66 74 79 70 4D 34 41 20 4 Apache Tika
66 74 79 70 4D 34 42 20 4 Apache Tika
66 74 79 70 46 34 41 20 4 Apache Tika
66 74 79 70 46 34 42 20 4 Apache Tika

Extension

.m4b

MIME Type

audio/mp4

Byte Offset

4

Risk Level

Safe

Validation Code

How to validate .m4b files in Python

Python 
def is_m4b(file_path: str) -> bool:
    """Check if file is a valid M4B by magic bytes."""
    signature = bytes([0x66, 0x74, 0x79, 0x70, 0x4D, 0x34, 0x41, 0x20])
    with open(file_path, "rb") as f:
        return f.read(8) == signature

How to validate .m4b files in Node.js

Node.js 
function isM4B(buffer: Buffer): boolean {
  const signature = Buffer.from([0x66, 0x74, 0x79, 0x70, 0x4D, 0x34, 0x41, 0x20]);
  return buffer.subarray(0, 8).equals(signature);
}

How to validate .m4b files in Go

Go 
func IsM4B(data []byte) bool {
    signature := []byte{0x66, 0x74, 0x79, 0x70, 0x4D, 0x34, 0x41, 0x20}
    if len(data) < 8 {
        return false
    }
    return bytes.Equal(data[:8], signature)
}

API Endpoint

GET /api/v1/m4b
curl https://filesignature.org/api/v1/m4b

See the full API documentation for all endpoints and parameters.

Frequently Asked Questions

What is a .m4b file?

A .m4b file is a M4B file.

What are the magic bytes for .m4b files?

The magic bytes for M4B files are 66 74 79 70 4D 34 41 20 at byte offset 4. These bytes uniquely identify the file format regardless of the file extension.

How do I validate a .m4b file?

To validate a .m4b file, read the first bytes of the file and compare them against the known magic bytes (66 74 79 70 4D 34 41 20) at offset 4. This is more reliable than checking the file extension alone, as extensions can be renamed.

What is the MIME type for .m4b files?

The primary MIME type for .m4b files is audio/mp4.

Is it safe to open .m4b files?

M4B (.m4b) files are generally safe to open. They are classified as low risk because they primarily contain data rather than executable code. However, always ensure files come from a trusted source.