M4B
audio/mp4
Magic Bytes
Offset: 4
66 74 79 70 4D 34 41 20
The M4B file format is an MPEG-4 audio container developed by Apple Inc., functioning identically to M4A but specifically designated for audiobooks and podcasts. It is primarily used for distributing long-form audio content that requires embedded chapter markers and bookmarking capabilities to resume playback. While standard files are generally safe, content purchased from the iTunes Store may contain FairPlay DRM encryption to restrict playback to authorized devices.
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 offset: 4 bytes
"""
signature = bytes([0x66, 0x74, 0x79, 0x70, 0x4D, 0x34, 0x41, 0x20])
with open(file_path, "rb") as f:
f.seek(4)
return f.read(8) == signatureHow to validate .m4b files in Node.js
Node.js
function isM4B(buffer: Buffer): boolean {
// Signature offset: 4 bytes
const signature = Buffer.from([0x66, 0x74, 0x79, 0x70, 0x4D, 0x34, 0x41, 0x20]);
if (buffer.length < 12) return false;
return buffer.subarray(4, 12).equals(signature);
}
Go
func IsM4B(data []byte) bool {
// Signature offset: 4 bytes
signature := []byte{0x66, 0x74, 0x79, 0x70, 0x4D, 0x34, 0x41, 0x20}
if len(data) < 12 {
return false
}
return bytes.Equal(data[4:12], signature)
}API Endpoint
GET
/api/v1/m4b
curl https://filesignature.org/api/v1/m4b