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Participating Frequently
July 21, 2025
Question

Fading Trail with a Moving Camera

  • July 21, 2025
  • 2 replies
  • 130 views

Hey there guys,

 

I've been asked to do something for a skating company where a trail is produced behind the skater in some footage. This is easy enough to do, as I can just Mocha track the skater then draw a stroke path on that track, but the problem comes with trying to keep that trail stuck to the ground afterwards.

 

If I do the Mocha track, then 3D cam track the footage then stick a camera in, the Mocha track just warps out of place.

 

What do you think would be the best workflow for this. Track first, then maybe just draw on the path afterwards?

 

I might be thinking of this completely backwards haha, so please give me some ideas if you have another way of approaching.

2 replies

Participating Frequently
July 23, 2025

I had to make a WIP of this yesterday so had a go myself. I created a 3D camera track, then drew on the path with the pen tool. Becasue my clip is 40 seconds and the camera is moving really fast, I had to separate the drawn paths up and attach them to different solids along the skater's path that I created with the 3d cam track. Still, the track wasn't 100%, so when some of the trails were disappearing out of view, I had to manually keyframe them back into position.

 

Honestly a bit of a manual keyframe nightmare!

 

I'm going to have to do a lot more of these shots in the next few months, so still looking for any tips here.


My main concerns still:

 

1. I need to draw a path behind the skateboarder. It can literally just be a straight white line. Something I noticed with using the pen tool is that even when made 3d, you can't move the points in 3d space. What would be a solution to create a stroke path that I can dynamically change each point in 3D space? Then I could just cam track, and reference various nulls along the path.
2. If you have one very long shape, but only one cam track, I noticed that the back of the shapes warp as they go out of view (imagine a top down view here, with a drone camera moving along the Z axis, so the floor keeps moving out of view). Is the solution here to do what I did? And just create many solids, and split my layer up?

 

Thanks - any other thoughts very welcome

nishu_kush
Community Manager
Community Manager
July 21, 2025

Thanks for reaching out, courtlined245.

 

If the camera has movement, I think the 3D camera tracking is essential for such shots. If you could share a small clip from your footage, that'll give us a better idea.

Hope it helps.


Thanks,
Nishu

Participating Frequently
July 21, 2025

Hi Nishu,

 

I can't provide the exact clip due to an NDA, but here's a link to a fairly similar clip:

https://www.pexels.com/video/skaters-in-parking-lot-7645466/

Imagine the camera is directly behind the skater on the left from about 6s in. The camera is following behind her (in my clip, the camera is further back so more space to see the trail). Imagine that the skateboard had paint on the wheels and was essentially drawing a line as she skates - that's essentially what I want. The trail can just be a drawn path - it doesn't have to be particles etc.

Hope that gives you some more context!

 

J