You can use effects like Write-On to draw your path by referencing their position control. Likewise, any particle effect that can leave a "trail" can be used.
Maybe a trail isn't the right word, ehm... A line that follows the exact path of the barbell.
I would apply the tracking information to a null. Then I would reveal the position property of that null, select all of the keyframes by clicking position and then copy. I would then deselect all layers, choose the pen tool (G) and click anywhere in the composition panel to start a new shape layer with no fill and a solid color stroke. After you have started the path paste (Ctrl/Cmnd+v) to create a stroked path that follows the null. You can then add "trim paths" to animate the line and time it to the movement.
You need to add and animate trim path to match the timing of the move.
1) I open the .mp4 (the video) in a new comp
2) track motion
3) new layer > null object
4) click on the .mp4 > edit target (at the tracker) > null object
5) apply > x/y
6) click on the null object > go to position > ctrl+c
7) deselect all > press G > click in the comp panel (no fill / solid color stroke) > ctrl v
8) and then? i tried adding a stroked path and a trim path to the new shape (the ctrl v part)
Thanks in advance
Rick, once again, thank you for helping me.
But, I still can't get it working
Let me try to explain again what I am trying to achieve, maybe I gave you got the wrong idea.
As soon as the squat starts, I want a line to follow the barbell, with the exact same speed (live speed).
So when I play the video, the line follows the barbell. So after 1 rep theres 1 line that goes down and up, and when I start the 2nd rep, the 2nd line appears...
Already explained how to do that. Try this to get the idea.
- Start a new comp 10 seconds long
- Use the pen tool to draw a path with no fill and a 10 pixel stroke
- With the shape layer selected press the U key twice to reveal all modified properties of the layer
- Use the Add button to add trim paths
- Add a keyframe for to the End property and set the value to 0 and the line should disappear
- Move the CTI to the end of the timeline and change the end value to 100
Apply this principal to the path you are trying to animate. You'll will have to add multiple keyframes and make adjustments to get the timing to work out perfectly.
You will have to carefully go through the timeline and animate the end point. If you want to have multiple lines then you will have to duplicate the path and adjust both start and end points. There is no automatic way to precisely pick up the timing of the motion path. You could write an expression that tied the percentage of completion of the motion path of the null to the percentage of the End property of trim paths (or stroke or paint) but it would be too complicated for me to write it without going into AE and trying to figure it out. It might be a good thing to create and save for future use as an animation preset but it would not be a task for a beginner.
Thank you Rick, it's working.
Im surprised though that there's no automatic way to do this....
Thank you, once again.
There is a way to do it more automatically, but that involves a completely different way of making the line. As they say, there is more than one way to skin a cat in AE.
You would use expressions to tie the position of an emitter in a particle effect to the position of the null object. Then, simply adjust the particle settings to fade or shrink over time so that you have a line drawing on and fading out.