Playing encrypted video

Question

What I want to do is next: We need to protect the video content(encrypt it) and be able to play it.

Tricky part is that we do not want to load everything into memory

Answer 1

Just about every widely used encryption algorithm works on blocks of sizes between 128 and 256 bits – and will happily decrypt only a few of these at a time, just fine for streaming. Check out, e.g., Crypto++ for a software library that has streaming interfaces. (I.e., you just open a file, put a decrypting filter around that, and then just continue pretty much like with any other file.)