I've seen many questions about a classical A/B mixer with compositing possibilities "resolume style"
Needed something similar last saturday, so here is my WIP version: https://github.com/Kayoshu/MadmapperMaterial-ABMixer
It's based on "Cross Zoom Transition" from public library 2DFX, converted into a material, nothing is changed on automation/audio detection
It's provided "as it is", screenshots for usage/outputs setup are on github
No support, no further update, I will tailored my own version for my own need
Some hardcoded parameters, unfinished aspect ratio experiments ...
Copy it, modify it with your own transitions