How to track face in 2 videos?

[ad2806]

Hi guys

I have been using AE and trying to get to track a a face with Mocha. In the first video I can track the face which is coming down some steps and turning away.

How can I track or copy(?) a face in another video and replace it, this one is more stationary than the first video.

Any help would be great, I can do it with a still image but video to video now sure.

Thank you

[Roland Kahlenberg]

In mocha, you draw a tracking spline onto a new layer, in mocha's layer stack. When you paste data in AE, after tracking, you can choose which mocha layer is the source.

[ad2806]

Do I need 2 null objects for both videos? I kind of got it to work but tracking was out

[Roland Kahlenberg]

Yes - one Null for each tracking data - I am assuming you are pasting Transform Data.

[ad2806]

yes pasting the transform data to each null object, its after this I am getting stuck. If i link video 2 to 1 the whole video will follow the link 1 track, vice versa.

[Roland Kahlenberg]

i'm now having difficulty understanding your issue. You'll have to provide screengrabs or screen captures.

[ad2806]

ok so i can paste the mocha tracking from both video clips, then i want to link the face from video 1 to video 2. I am using the pen tool (should I be?) to go around the face but when linking that to the video it sort of follows the track data but not 100%, maybe too much movement in the video.

Maybe I am missing something or just doing it wrong way?

[Rick Gerard]

If I follow you correctly you have one video with someone coming down some steps. You want to replace the face of that actor with video of another actor in another location.  Here's the most logical way to approach that problem.

1. In the main composition Motion Track the face of the Actor coming down the stairs using Mocha or AE's motion track or even Mask Tracker
2. Transfer the tracking data to a placeholder solid so you can see how accurate the track is and how accurately the placeholder follows the first actor's face.
3. In a separate composition, Motion stabilize the second actor's face so the face does not move in the frame
4. Mask the second actors face using Rotobrush or Rotoscope to eliminate the background
5. Compare the timing of the head turns with the first actor
6. Apply Time remapping and adjust the timing to the motion stabilized copy of the second actor so the heads turn at approximately the same time
7. Resize the motion stabilized comp so that it just includes the face of the second actor
8. Back in the Main Comp replace the placeholder solid with the sized and second comp of the stabilized actor and scale appropriately so the face completely hides the original actors face.

The best way to motion track the first actor and motion stabilize the second actor depend entirely on the footage. The re-timing accuracy of the motion stabilized actor depends on the final look you are going for. A few years ago I did this for a realistic face replacement of an actor that was running down a sidewalk with half of his face missing. We filmed the fake head while watching the original performance so we could get the timing of the head movement down correctly, then just followed the eight steps I outlined to replace the face with the fake head. You could not tell that the actor had not spent the better part of a day in a makeup chair getting prepped for the shot.  I have also done face replacements that were not intended to look real. Same workflow, just a lot less time involved.

[ad2806]

Thanks Rick, works well but I have one issue where the roto tool only removes the back ground for about 30 odd frames?

[Rick Gerard]

You'll need to go through the User Guide and study up. Rotobrush is almost impossible to figure out without doing some homework. Just type rotobrush in the Search Help field at the top right corner of After Effects.  Depending on the shot you might be better off just doing the roto by hand. Post a screenshot of the stabilized video and I can give you a better idea of how I would do it.