It depends on what do you attempt to do with the encrypted files. If you distribute them you'll need private/public key encryption. Called also asymmetric. If you want them just encrypted, "simple" password encryption will do the job. You have to chose the level of security you want. Most of the algorithms are compromised. Some of them deliberately. If want
security, stay away from any RSA encryption regardless it is a standard now. Stay away from any DES, DSA algorithms. Almost deprecated recently.
The obvious choice is ECC ( elliptic curve cryptography) 192, 256, 384, 521. ECC with 256 bits key is considered secure as DH, DSA, RSA with 3072 bits length key.
If you want a real encryption yet unbreakable, pay attention to One-time-pad. You are saying that the app will encrypt videos. If you use this encryption, you have to keep somewhere a big file
random ( not all random generators are truly random ) data as a key. I think it is not practical for such a task.
See
PyNacl module for encryption/decryption and
bcrypt,
passlib for hashing the passwords. You may see and GPG. There are
several modules for this. GPG is useful because you can interact with other applications that are using PGP.
Don't forget to check what level of security you can use in legal. As I know there are restrictions in the USA, if you live there, for the encryption level used in the software.