@zombie this isn't a guide for Creating a CDI from scratch, there's a lot of extra steps involved like finding LBA specific hex values in the binary (primitive copy protections), downsampling dreamcast specific formats like ADX audio or SFD video, etc
this is a guide for extracting a working pre-made CDI image for the purpose of modding or research
if you want to make a CDI from scratch, refer to this guide, its how i learned all this
https://pastebin.com/jfFs6jdMLBA 45000 is the standard LBA from almost all retail GD-ROMs