Proper preparation and planning for the filming, quite a bit of rotoscoping to blend in the overlays. Basic compositing stuff. No magic buttons, just hard work.
I'm not pro. Could u explain step by step please?
If I were teaching that technique in a college class we would spend about 3 or 4 days on it. Here are the steps you have to follow.
- Plan you camera shots so that the angle and distance between the camera and the actors are as close to identical as possible. Perspective is controlled by camera position
- If you have moving cameras in the production figure out a way to get repeatable camera moves that are as close to identical as possible
- Match the lighting as closely as you can between shots
- If you have complicated backgrounds shoot clean plates so you have something to use to fill in the holes you create when removing things like the actors heads
- Learn how to do camera tracking, point tracking, shot stabilization so you can track the position, scale and rotation of the heads you want to replace
- Learn how to do Rotoscope and keying so you can separate the actors heads and or bodies from the background
- Learn about color correction and color grading so you can match the color and quality of the shots
Now you take your original footage and the footage of the replacement actor into AE, you track and stabilize each shot so that the actors heads are as stationary in the scene as you can make them. You roto both heads out of the shot. You add your clean plate in the background to fill the holes made by removing the original actors head. You position and scale the replacement head over the original actors body. You then put the movement back in the shot by removing the stabilization from the original footage and adding the motion of the original footage to the replacement actor and the clean plate the is fixing the background. Then you color grade your composite to make things match.
The simpler your shots and the more stationary your actors are the easier this is to get done. The example had a bunch of stock footage which requires a bunch of careful analysis and planning. I think I'll revise my original estimate. If this were a class we could easily spend 2 weeks trying to reproduce this video even in a simple way. Like Mylenium said, it's not magic, it's just hard work.
Thank you! I appreciate