".mp4" is just a file extension, the source of the colloquial name for the container. But both the container and the codec are named MPEG-4 and both are colloquially called "MP4."

"Box level" is apparently referring to types of cryptography, "S-boxes are non-linear transformations of a few input bits that provide confusion and P-boxes simply shuffle the input bits around to provide diffusion"[1] The basic function of S-Box[2] is to transform 8 bits input data into 8 bits of secret data using a precomputed look-up-table (LUT). A "permutation box (or P-box) is a method of bit-shuffling used to permute or transpose bits across S-boxes inputs, retaining diffusion while transposing."[3]

[1] https://www.linkedin.com/learning/symmetric-cryptography-ess...

[2] https://en.wikipedia.org/wiki/S-box

[3] https://en.wikipedia.org/wiki/Permutation_box