mp4 の構造

とりあえず root の box とそのペイロードサイズを列挙してみた

あと ftyp については内容も読んでみた

実行結果

code::

$ python analyze.py mito.mp4

code::

Metadata:

major_brand : mp42

minor_version : 0

compatible_brands: isommp42

一致！

コード

code:mp4.py

import sys

from pathlib import Path

def identify_next_box(fp):

box_size = int.from_bytes(fp.read(4), 'big')

if box_size == 0:

return None, 0

box_type = fp.read(4).decode()

header_size = 8

if box_size == 1:

box_size = int.from_bytes(fp.read(8), 'big')

header_size = 16

return box_type, box_size - header_size

def read_ftyp(fp, ftyp_payload_size):

major_brand = fp.read(4).decode()

minor_version = int.from_bytes(fp.read(4), 'big')

compatible_brands = []

for i in range((ftyp_payload_size - 8) // 4):

cb = fp.read(4)

compatible_brands.append(cb.decode())

return major_brand, minor_version, compatible_brands

def main():

fp = video_file.open(mode='rb')

while True:

box_type, payload_size = identify_next_box(fp)

if payload_size == 0:

break

if box_type == "ftyp":

continue

fp.seek(payload_size, 1)

fp.close()

if __name__ == "__main__":

main()