Python Get MIME of s3 object on Lambda

I have a lambda that triggers upon s3 PutObject. Before proceeding the lambda needs to check if the file is actually a video file or not (mp4 in my case). File extension is not helpful because that can be fake. So I have tried checking MIME using FileType which works in local machine.
I don’t want to download large files from s3, just some portion and save in local machine to check if that’s mp4 or not.
So far I tried this (on local machine) –

import boto3
import filetype
from time import sleep

REGION = 'ap-southeast-1'

tmp_path = "path/src/my_file.mp4"

start_byte = 0
end_byte = 9000

s3 = boto3.client('s3', region_name=REGION)

resp = s3.get_object(
    Bucket="test", 
    Key="MVI_1494.MP4", 
    Range='bytes={}-{}'.format(start_byte, end_byte)
    )

# the file
object_content = resp['Body'].read()

print(type(object_content))
with open(tmp_path, "wb") as binary_file:
    # Write bytes to file
    binary_file.write(object_content)

sleep(5)
kind = filetype.guess_mime(tmp_path)
print(kind)

But this always return None as mimetype. I think I am not saving the binary file properly, any help would really save my day.

TLDR: Download small portion of large file from s3 -> save in tmp storage -> get mime.