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Motion / camera tracking and applying to complex background: Finding a solution

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Laszlo Gabeli
Motion / camera tracking and applying to complex background: Finding a solution
on Dec 11, 2018 at 10:18:45 am

Dear AE wizards,
I'm relatively new to AE. I've been working on my first project for a few weeks now, which would be a music video for my own band. I feel that I've already learned a lot and slowly but surely I'm making progress. However, I have a specific problem that puzzles me, and I'm trying to find the best solution for it. First, let me introduce the concept and the source materials I'm working with:

- Fixed angle, full body green screen shots of the band members, shot from a tripod
- Hand-held close-up shots of some band members (2d motion tracking of these footages is possible most of the time)
- Using a large ground texture as the ground plane
- An HDRI environment mapped to a sphere in Element 3D
- A video footage of moving clouds in the background

Here are two shots from the project. Obviously there's still no grading/lighting done to the actors and the background, so please don't judge it by that yet. Also, the drummer is still to be added in the background.




Everything is placed in the 3D plane, and a single camera moves around the actors during the whole video. Sometimes it moves quickly closer to an actor (with motion blur turned on), and that's when I would like to utilize the hand-held close-up shots (as seen on the 2nd screenshot). I managed to get a good result by lining up the close-up shots with the stills and keyframing the opacities during the camera movement. The problem I have is the static background while showing the hand-held close-ups. I need the background elements (and some actors in the background) to be in sync with the movement of the hand-held camera. What would be the best way to achieve this? I'm thinking about motion tracking the footage and then parenting the BG elements to that tracker, however, it would be a pain in the ass, as I can't "unparent" them when the tracker's not needed. Maybe I would need to duplicate all BG layers and use them separately.

However, I think it would be a better solution to extract (track) the camera motion data from the real camera and apply it to my virtual camera in a separate comp of the background. Maybe I can use the 3d camera tracker tool for this? I'm experimenting with that right now, however it's been solving the camera of a 30sec. clip for hours, and I'm not even sure it will work.

Anyways, I would like to know if there's a good solution for this, and how it would be addressed by more experienced users. Obviously I learned my lesson, and I'm not going to shoot hand-held shots anymore for projects like this. I should have shot the close-ups with a tripod as well and pull of all camera movements in AE, but I would like to know if I can still do something with this. :)


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Richard Garabedain
Re: Motion / camera tracking and applying to complex background: Finding a solution
on Dec 12, 2018 at 5:40:22 pm

I would just add a wiggle expression to the camera or background....ALT click position of the camera and type in wiggle(3,15) thats 3 times a second it moves 15 pixels..you can change your numbers til it matches close...


Also this expression might help out. if your characters are 3d then you can alt click the Y rotation and paste in

delta = toWorld(anchorPoint) - thisComp.activeCamera.toWorld([0,0,0]);
radiansToDegrees(Math.atan2(delta[0],delta[2]))

this will make it so the people are always facing the camera


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Laszlo Gabeli
Re: Motion / camera tracking and applying to complex background: Finding a solution
on Dec 13, 2018 at 7:16:04 pm

Thanks for pointing me out the wiggle expression. I haven't used it yet, but it will certainly come handy in future projects. However, in this particular project I ended up spending hours with tracking the background on the close-ups where needed, and then I applied all tracking info to a single null tracker, which I used as a parent for every background layer. The only trick I had to do is to reset the null tracker's position with a keyfream each time the camera moved back to the static (tripod-shot) objects. I think this did the trick, however I still have to wait a night to see the end result in full resolution (it's rendering right now). Anyways, thanks for the handy advice.


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Kalleheikki Kannisto
Re: Motion / camera tracking and applying to complex background: Finding a solution
on Dec 15, 2018 at 5:06:05 pm

Kinda late on this, but I would stabilize the handheld shots so everything is locked down in your comps and add the camera position wiggle afterwards. If you wanted the wiggle only on closeup shots, you could then link the wiggle amount to a slider that you can animate the value of.

Kalleheikki Kannisto
Senior Graphic Designer


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Max Haller
Re: Motion / camera tracking and applying to complex background: Finding a solution
on Dec 18, 2018 at 3:38:38 pm

I guess its too late to help with this project, but here's a link to a post about an expression you can apply to a slider control to switch which null a layer is parented to. https://forums.creativecow.net/docs/forums/post.php?forumid=227&postid=2402...

something like this might help if anyone else is looking for a way to switch parented nulls. I don't think it literally changes the parent property of a layer but you can switch the null it's taking the position/rotation/scale values from which is essentially the same idea.


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