crypt_files.py

from Crypto.Cipher import AES
from Crypto.Util import Counter


def encrypt_file(key, in_filename, out_filename=None, chunksize=64 * 1024):
    if not out_filename:
        out_filename = in_filename + '.enc'

    counter = Counter.new(nbits=128, initial_value=0)
    encryptor = AES.new(key, AES.MODE_CTR, counter=counter)

    with open(in_filename, 'rb') as infile:
        with open(out_filename, 'wb') as outfile:
            while True:
                chunk = infile.read(chunksize)
                if len(chunk) == 0:
                    break
                elif len(chunk) % 16 != 0:
                    chunk += ' ' * (16 - len(chunk) % 16)

                enc = encryptor.encrypt(chunk)
                outfile.write(enc)


if __name__ == '__main__':
    encrypt_file(bytes('a_really_strong_password', 'utf8'), 'd.mp4')