Any theoretical limit to compression?

Question

Imagine that you had all the supercomputers in the world at your disposal for the next 10 years. Your task was to compress 10 full-length movies losslessly as much as possib

Answer 1

If you have a fixed catalogue of all the movies you were ever going to compress, you could just send an id for the movie and have the "decompression" lookup up the data with that index. So compression could be to a fixed size of log2(N) bits, where N was the number of movies.

I suspect the practical lower bound is rather higher than this.

Do you really mean lossless? Most of today's video compression is lossy, I thought.