#!/usr/bin/env python3

# ========================================================
#    This code is for study only.
#    This code is not optimized.
#    This code is over simplified.
#    This code doesn't respect rules of good coding.
#    This code has duplicate codes: 
#        to understanding without complexity.
#    Some values -useless on code- will not be converted.
# ========================================================

import sys

# Conversion en int
def to_int(length : bytes = b'') -> int:
    return int.from_bytes(length, byteorder='big')

if len(sys.argv) < 2:
    print("Usage: %s <mxf>" % sys.argv[0])
    sys.exit(1)

mxf_file = sys.argv[1]

with open(mxf_file, "rb") as file:

    while True:

        # Key : Universal Label
        key = file.read(16)

        # End of file
        if not key: 
            break

        # Length (BER format)
        length = to_int(file.read(4)[1:])  # BER format - read last 3 bytes

        # Value
        value = file.read(length)

        # Filter by KLV "Picture Essence"
        if key.hex() != "060e2b34010201010d01030115010801":
           continue

        # Show each KLV
        print("{key} - {length:>6d} bytes - {value}...".format(
            key    = key.hex(),
            length = length,
            value  = value[0:16].hex()
        ))

        # write Plaintext to file
        filename = "output_%d.j2c" % file.tell()
        print(f"Extract {filename}")
        with open(filename, "wb") as f:
            f.write(value)