Motion Track a static shot with crop

[Mark Suszko]

Mmm, tough… the way to have done this would have been to have each dancer on blue or green screen. If they are wearing light colored leotards, you might see what luminance keying could do for you. But you’ve pretty much committed yourself to rotoscoping and motion tracking with the shots you describe.

[Devin Terpstra]

Sorry Mark, guess I didn’t explain very well. I’m thinking of having all the clips on the screen in boxes, like a Zoom call, so a 3×3 grid of individual dancers. I’d like to keep each near 100% scale so they aren’t tiny on the screen. I’d like to keep them in the center of their box using motion tracking and cropping. Now, they can dance from one side of the screen to the other. I did a test of motion tracking and It kept the dancer in the middle of their screen, but when I crop it, the crop just keeps the same position of the stage.

[Mark Suszko]

Okay, this IS doable, because I’ve done something like it that uses the same underpinning effects.

My application is a little different: it’s putting a speaker in a cropped box and moving that box to the side of the screen so another source of graphics like a powerpoint slide can be seen next to them. I use a 3-d effect plug-in in final cut to turn these two image panes in 2-d space, and align them like a partly-opened book, so they fit a 16×9 frame better and retain readability of the slide. The same effects I use for that, you can use in your problem, because that 3-d effect plug-in allows you to independently move and keyframe the centering of the source footage, inside the rotated box. I used that feature with a speaker that constantly wandered a foot or two to the left and right during a long locked-off shot. The keyframing only took a few clicks to do but kept the speaker smoothly centered in my box as if tracked by a live camear. Now, I couldn’t automate that, but if your grid of dancers is only 3×3 it’s not going to take forever to keyframe them to stay centered.

The 3-d plug in, I got from a search on FCPX.io …. I think maybe it was made by Alex3d. There are a couple of free 3-d effect plug-ins for FCPX like this. I’m not going to hunt them down for you though, but now you know about them I think you can find them on your own.

[Devin Terpstra]

Thanks Mark, I can’t wait to take a break from making fake zoom screens to do a little research. I appreciate the direction.

[Mark Suszko]

Another way to skin this cat is in Apple Motion by making each box a dropbox. Drop-boxes contain additional sub-controls in the Inspector that allow you to adjust the source scale and position inside the dropbox.

What would make your project easier and more efficient, is to build it all in Apple Motion. Create the first drop-box, then copy>paste it to make your array. Drag each source into one drop-box and then adjust the scaling and keyframe the positioning to keep each dancer centered. While that may seem tedious, there is a fast way to get it done: you keyframe the first, last, and middle keyframes. Then pick a spot midway between those two keyframes, check it and adjust it. Then again find a mid-point between established keyframes and rinse/repeat. You’ll generally find this covers 90 percent of your needs with only a relatively few manually set keyframes. You want to make the machine do as much of the work as possible for you.

Advice if you’re going this route: pre-prepare every clip to align with the first note of music, or a shared synch event BEFORE you start working with these tracks in Motion. Import only the pre-aligned tracks.

You might also look at the earlier threads in this forum and maybe the Motion forum about “Virtual Band Concert”… there were a lot of helpful tips submitted there that can be applied to what you’re trying to do.