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Well, I think you are confusing two different workflows here. What you describe sounds more like you actually want to use a track matte. For that, you'd cut out whatever shape you desire, put it on top of your otehr layer, then in the bottom layer assign the top layer e.g. as an Alpha Matte. That matte layer can then be conventionally tracked like any other layer. Masks on the otehr hand are not trackable - well, at least not directly. For that, you'd use Null objects to follow certain positions where your mask vertices are supposed to be, then use scripts like TrackerViz or Tracker2Mask (freely downloadable e.g. via links on aescripts.com or xscriptorium.com) to transplant the Null position data to the actual mask points.
Currently, there's no direct (or at least a built-in) way to apply motion tracking data to a Mask's position. One user did write a script that allows to apply tracking data to individual mask vertices.
However, what many users do is: apply the mask to a soild layer, apply tracking data to the that layer's position, and then set the solid as an alpha matte for the layer you want to mask.
Once said that, bear in mind that After Effects Help on the web not only has the full contents of the manual, but it's also an amazing, community-based resource which points to a lot of tutorials, forum posts and many other useful bits. if you perform a search for "tracking masks", you'll be delighted with the amount of information you'll find
Thanks to Mylenium and Adolfo!
I was asking the wrong question, obviously. Anyhows - I was able to do it! ! duplicated a car running on a road, a rather funny effect, the two identical cars running at the same distance.from each others. The Centerpoint property is crucial, without this, I had not been able to do it. Hope I have understood it right.
..which points to a lot of tutorials..
They are good, but I miss very simple, basic tutorials, explaining the most basic things, like this. Many of the tutorials are overcomplex, IMO, and many f them are a little too result oriented, IMO, trying to accomplish certain tasks, whereas I prefer tutors explaining the principles only. When this is said - the amount of tutors is impressing.
They are good, but I miss very simple, basic tutorials, explaining the most basic things, like this. Many of the tutorials are overcomplex, IMO,
They are complex because we searched for a quite complex subject - applying motion tracking data to masks. If we had searched for a simpler topic, like applying the alpha of a a layer to mask another, we would have gotten simpler results as well
Alfonso... I mean, Adolfo
They are too complex for my taste, menaing that they bring in too many topics in one tutor. Look at the tutors at videocopilot.com. Fantastic technical quality, super screen resolution, speed and accuracy - those writing these are heroes. Still they mix too many features in one tutor I think. Well, I feel this maybe because I am new to AE..
Alfonso... I mean, Adolfo
So you noticed this?! I corrected it within a fraction of a second, in less time than AE needs to render and track 10 frames