Pro Tips, Tutorials

Motion Tracking in After Effects: How to Use the Point Tracker

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As a VFX artist, one of the most fundamental skills to learn is motion tracking. With motion tracking, you can track the movement of an object and apply the data from that to another layer — one of the most common uses is replacing objects or attaching objects onto your scene, such as what you see on the screen of a mobile phone.

After Effects offers different kinds of motion tracking, such as the Point Tracker, which offers one-point, two-point, and four-point tracking. There’s also a built-in 3D Camera Tracker that allows you to reverse engineer a scene; a spline tracker that enables you to track masks on an object; and Mocha AE, a planar tracker from BorisFX. The Point Tracker is the most basic and the oldest tracker within After Effects, but it has some big advantages — one of which is allowing you to choose which features to track in a scene. It’s also the most flexible and versatile tracker in AE. Here’s how to work with it.

 

Single-Point Tracking

Single-point tracking is great for following the movement of an object — specifically objects that go left, right, up, or down. For this example, I’ll be tracking a dolly shot of a whiskey and some pills by Pond5 artist Burlingham.

I have three layers set up: the first is the footage that I’ll be tracking, the second is a Call-Outs AE template by adamshead, and the last is a null object, which will serve as the target for my track.

Select the layer, right-click, and choose “Track Motion.” This opens the Tracker Panel as well as the Layer Panel. Select “Track Motion” in the Tracker Panel.

The Motion Source is your selected layer. You can track different areas in a single clip and the Current Track tells you which tracker is currently active. As you can see, you can track Position, Rotation, and Scale. Since this is a one-point tracker, we are only checking Position.

There are also several Track Types within the point tracker. Choose “Transform.”

Areas to be tracked are specified by setting the track points in the Layer Panel. Each track point contains a Feature Region, a Search Region, and an Attach Point. Collectively, these three are called a “tracker.” In this shot, I placed the tracker in the corner of one of the white pills. This is what I’ll be tracking.

Feature Region: The Feature Region defines the element in the layer to be tracked. This should surround a distinct visual element, and it should be clearly identifiable in the duration of the track, even if there are changes in light, background, and angle.

Search Region: The Search Region is the area that After Effects will search to locate the tracked feature. The element you are tracking should always be within this region, but it can be resized to accommodate large movements of your element. Making the Search Region smaller results in faster tracking, but also runs the risk of the tracked feature leaving the search region entirely between frames.

Attach Point: The Attach Point is the actual point you are tracking. It’s where the target layer or effect control point will be placed. By default, this is positioned at the center of the Feature Region, but can be moved if needed.

Right now, I’m at the very first frame of the clip. Press the “Analyze Forward” button to start the tracking process. Take note that you don’t have to start at the beginning of the clip. You can start tracking even from the middle or end of the clip.

When the tracking is done, you’ll see that the tracker has generated keyframes for every frame of the shot.

Now click on “Edit Target,” choose “Null 1” and press “OK.” This tells AE to put all the tracking data created into the Null 1 layer.

Next, click “Apply” in the Tracker Panel. The Motion Tracker Apply Options will appear. When you’re doing single-point tracking, AE will always ask you where to apply the tracking data. Is it just on the X-axis? Y-axis? Or both? Choose “X and Y” and press “OK.”

The tracking data is now applied to the position property of our Null 1. The next step is to position your graphic in the composition and parent it to Null 1.

You can parent your layer by dragging the pick whip of the Call-Out layer to Null 1. In this example, I first went into the middle of the clip before I did my parenting, because this part of the footage gives me the best layout for my purposes.

You might be wondering why I applied the tracking data the Null and not the actual Call-Out graphic. It’s because applying our tracking data to our Null and parenting our Call-Out layer to it gives us more freedom, which means we can reposition our motion graphic any time or move it to a later part of the clip without destroying our track.

Here’s the result:

 

Two-Point Tracking

The process for two-point tracking is exactly the same as with the single-point tracker. The only difference is that there are now two trackers. By using a two-point tracker, we’re able to track not only position, but also scale and rotation.

I want to add some animated text to the door of this car shot by Pond5 artist JacksonKitchell. If you want to learn more about how to animate text in AE, check out my previous tutorial on How to Animate Text in After Effects.

The steps are the same as with the single-point tracker, except that now I’ll be turning on the other options so that I get two trackers. And since this is a dolly shot, I’ll select the Scale and the Rotation.

Here’s the result of my track. You’ll notice that I have two trackers, which I placed at the end of the car’s moulding. I then aligned my text and parented it to my Null object. I turned on my 3D switch to my text so that I can rotate it and match the perspective of the door. Then I added a mask so that the text only appears within that mask.

Here’s how my timeline looks. I’ve added another copy of the video and placed it on top of the text. I then added a keying effect called “Extract,” so that I can remove lighter and darker parts of the video, which helps a lot in compositing.

Here’s my setting for the Extract effect.

And here’s our video with the text on it:

 

Four-Point Tracking

As the name implies, this uses four trackers. These trackers analyze the relationship between four reference patterns, like the corners of a television, smartphone, or tablets. Unlike the single-point and two-point trackers, the four-point tracker directly applies the tracking data to an image. The tracking data is applied to each corner of an image or clip to “pin” the clip, so that it appears locked in the picture frame or television monitor.

The screen on this smartphone footage by prostockvideos is blank, so I want to replace and cover it with another image. The best tool to use in this case is the four-point tracker.

I’m going to insert this iPhone screenshot into the scene:

The same steps that you learned with the single-point tracker are also applied here. This time, however, you’ll be choosing “Perspective Corner Pin” and you won’t need to create a Null, because the tracking data is applied to the image you want to put on the phone.

You can see on the result here that I placed the trackers on the corners of the screen.

Make sure that your target is the screenshot, then press “Apply.” You’ll see that the perspective corner pin added a “Corner Pin Effect” on the image, as well as keyframes for the position.

And here is our final result:

 
When using the Point Tracker, always make sure that you choose features that have good contrast, a distinct and consistent shape and color, and as much visibility as possible in the entire shot. This is just a taste of how easy it is to do motion tracking in After Effects. We will talk about the other types of tracking available in AE in our next installment!

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