After Effects Motion Tracking Tutorial

I finally got around to cover a topic that I’ve wanted to do for a while now: motion tracking in After Effects :)

In this tutorial, besides watching Walter and The Devil fight it out, you will learn all about the concepts and the practical application of Motion Tracking!
Enjoy!

Motion Tracking Fundamentals

Motion tracking in itself is not a visual effect, but an essential tool to help you create visual effects. It allows you to track the motion of moving elements in your footage and extract information about their position, rotation and scaling.

You can then use this tracking data to control other layers in your composition and, for example, create visual effect elements and have them follow your tracked object.
This allows you to do things like have blood stains stick to walls during a moving shot, add a halo or other effect to follow your actor, erase objects from your scene and much much more.

Base Footage

If you want to do motion tracking in a scene, make sure the element you want to track stands out cleanly against the background while shooting your footage. A person dressed in black walking in front of a dark sky will likely be hard to track. You can make motion tracking easier by adding tape markers or other helpers to your actors or objects to make them easier to track.
It is MUCH easier to remove a tracking marker than it is to track an indistinct object!

For this tutorial, we are going to track Walter’s head as he walks through the shot and attach a halo to it :)

After Effects Motion Tracker Controls

To get started with motion tracking in After Effects, open the Tracker window by going to
Window -> Tracker.
A small tool window containing all the controls necessary for tracking your footage will appear on the screen.

Scroll to a time position in your clip where Walter’s head is fully in frame, make sure the footage layer is selected and click on the ‘Track Motion’ button in the Tracker window. Since we also want to track the rotation of Walter’s head, make sure the ‘Rotation’ checkbox is ticked. You should now see 2 track points overlayed onto your footage, connected by a white line.

Motion Track Points

If you zoom into your track points, you will notice that each of them consists of 2 rectangles!

The inner rectangle defines the part of the frame we want to track. Make sure you position it on a very distinct and high contrast element that is easy to follow visually from frame to frame.

The outer rectangle defines the area that will be searched each frame to locate the contents defined by the inner one. Make sure it is big enough so that the element you are tracking remains within its borders across consecutive frames.

Notice that the larger you make the rectangles, the more processing After Effects will have to do and the slower the motion tracking calculations will become. Also note the small arrows on the white line connecting the 2 track points.
Track Point 1 will define the position data we are recording and Track Point 2 is used to record the angle i relation to Track Point 1 and store it as a rotation value.

Before we can get started tracking the footage, we need to understand what Null objects are and how we can use them to store our tracking data!

Null Objects

Before we get started with the motion tracking, we need a place to store our tracking data. For this, a Null Object will be perfect. You can create a new Null Object by selecting
Layer -> New -> Null Object.
I called my layer ‘HeadTrack’ as we’ll be tracking Walter’s head :)

A Null Object is merely a placeholder object with a transform that contains position, rotation and scale data. You can animate these properties or add other custom properties to the Null Object and then use the Null to control other layers in your composition. A Null Object will never be rendered.

We will use the Null Object to store our position and rotation data from motion tracking Walter’s head.

Tracking The Footage

Position the track points on the element you want to track. For me, I will place them on the back of Walter’s head and on his hairline as I want to track the position and the rotation of his head.
Once you positioned your track points, you can start the motion tracking process by clicking on the ‘Analyze Forward’ button in the Tracker tool window.

After Effects will now, frame by frame, process your footage and try to keep track of the elements you specified with the track points. If at any point in time the track points fail to follow what you expected them to, you can stop this process, go back, reposition the track points and continue the process from where you left of :)

Sometimes you have to fix a few small things manually or help the motion tracking process along, but eventually you should end up with having your track points follow the object you are tracking nicely.

Apply Motion Tracking to Null Object

Now that we have the track points follow Walter’s head, we can apply the motion tracking data (position and rotation) to our HeadTrack Null Object. For this, click on ‘Edit Target’ in the Tracker tool window and select the HeadTrack layer. Then click on ‘Apply’, select ‘X and Y’ and click OK.

Now when you scroll through your clip, you should see the Null Object follow Walter’s head correctly through the shot :)
You may have to manually fix up parts of the track, for example, where your actor enters or exists the frame. I fixed up the track for the HeadTrack Null Object manually.

Parenting The Effect Layer To The Null Object

Finally, I’ve created a nice glowing halo effect that we will now attach to Walter’s head :)
Go to any frame in the footage and position the halo nicely over Walter’s head.

We now want to parent the halo layer to the Null Object layer. You can do this by selecting the pick whip in the ‘Parent’ column for the Halo layer and dragging it onto the HeadTrack Null Object. This will make the HeadTrack layer the parent of the Halo layer.

Now, every change in position, rotation and scaling that occurs on the HeadTrack layer will automatically be applied to the Halo layer. Since we used motion tracking to make our HeadTrack Null Object follow Walter’s head nicely during the clip, so will our Halo layer :)

The Result

You can add more effect layers and have them follow Walter’s head by parenting them to the HeadTrack Null Object. I added a nice glow for the halo to make it look a little more convincing :)

You can use motion tracking to trace the movement of any element in your footage (as long as they have distinct features you can track), store the data in a Null Object and then use the Null Object to attach effect layers or control all sorts of other effects with it :)

Motion tracking is a fundamental part of knowledge for any visual effects artist and I am sure you will have lots of fun with it! :)