MP4 MPEG-4 Part 14

SIGNATURE = bytes.fromhex("66747970")
OFFSET = 4

def is_mp4(path: str) -> bool:
    with open(path, "rb") as f:
        f.seek(OFFSET)
        head = f.read(len(SIGNATURE))
    return head == SIGNATURE

const SIGNATURE = [0x66, 0x74, 0x79, 0x70];
const OFFSET = 4;

// bytes: a Uint8Array / Buffer holding the start of the file
export function isMp4(bytes) {
  return SIGNATURE.every((byte, i) => bytes[OFFSET + i] === byte);
}

package fileid

import "bytes"

var ismp4Signature = []byte{0x66, 0x74, 0x79, 0x70}

const ismp4Offset = 4

func IsMp4(b []byte) bool {
	end := ismp4Offset + len(ismp4Signature)
	if len(b) < end {
		return false
	}
	return bytes.Equal(b[ismp4Offset:end], ismp4Signature)
}

const SIGNATURE: &[u8] = &[0x66, 0x74, 0x79, 0x70];
const OFFSET: usize = 4;

fn is_mp4(bytes: &[u8]) -> bool {
    bytes.get(OFFSET..OFFSET + SIGNATURE.len()) == Some(SIGNATURE)
}

<?php
$signature = "\x66\x74\x79\x70";
$offset = 4;

function is_mp4(string $bytes): bool {
    global $signature, $offset;
    return substr($bytes, $offset, strlen($signature)) === $signature;
}