What do the presets actually do?
It would be great if it's easier to find out what the presets actually do, what options they translate to. A table like https://x265.readthedocs.io/en/master/presets.html would be very helpful but just having all the information in one place in the code will make the presets much easier to understand.
Right now the information is scattered in various code files. To make it worse, the code that maps presets to parameters is full of #if/else macros (example 1, 2) that make it impossible to quickly see what the code does. Can these macros be cleaned up? Why are they needed in the first place? They seem to be duplicating the functionalities of the version control system.