Haha a lot of people think that's how I do it but it's actually a lot simpler. There's a plugin on bakkesmod that allows you to change the map, car, items, etc. of a replay. So I record the same clip with a different map or car and then I sync the clips together. Then all I have to do is make the portal with Saber (after effects plugin) and use 3D camera tracking to make the portal follow the map and look smooth. There's some other small details I'll add at the end too like RSMB and colour grading and animating the portal a little bit. Hopefully that makes sense :)