Line animations

Question

If you watch the above video at 29seconds, there's a line that is drawn around the number 1. Many of these animations are littered throughout this video (again at ~1:02) and I'm wondering how I can create this effect in AE?

To be more specific, the main part of the animation I want to create is the "trailing" effect the line has. The tail tries to catch up with the head of the line, the tail doesn't just stay at the beginning, it follows the same path of the head of the line.

If there's a tutorial I can follow that'd be great. Sorry I don't know what this animations are called.

Answer 1

Create a mask on the layer you want to apply the effect to. In that case in the form of a circle but it can be any desired shape of course.

Then apply the "Stroke" effect on the same layer and in the "Path" option of the effect you choose the circle mask you just created. The Stroke effect allows you to animate start and end point of your line individually, enabling you to create exactly this effect.

The grey area is just to visualize that this is the mask I drew.

Answer 2

This can easily be achieved using a write on effect and altering the start and end point positions independently. You make a path that you want the line to follow and you then have the start point of the line animate slightly more slowly than the end point, resulting in the end slowly catching up.