It's actually not very difficult, you need some footage filmed on a tripod and adobe premier. Here you can see 2 scenes simply put them on top of each other now you can adjust the yellow line, that will make the upper video transparent that's the first way to be twice in one video.. second way, in case you dont want to be transparent: don't use the yellow line, pull it back to 100%. Now open the effects menu (if you cant find it: window -> effects) now you have to translate by yourself.. that's how it looks in the german premier: just pull the effect "over" the upper scene open the effect control / properties.. i don't know how it's called in english. select the upper video, now you can see a dropdown menu, called sth with "scale" now you can cut the video, in % i pulled the value to 29% "right", you can see its not enough, because you can't see the second me complete. On 50% i can see both "me". basically that's it.. you just have to end the effect, when one person left the screen. Try to play with the effect, after a few minutes it won't be a big deal