Motion tracking is a technique that involves recording and replicating the motion of objects and cameras in the scene. It’s quite versatile and it can be done in After Effects. A tracker is a tool used to track an object or point in footage. What can usually be seen on the green screen are crosses, which are references or anchor points to put the footage in, called markers. You select a pattern or area of contrast for the tracker to reference (markers help with this) and the tracker looks for that specific pattern in every frame and image, by referencing the start point and record the distance and direction travelled, doing this every time from the last recorded position. This is why it’s called motion tracking. There are some things that the trackers ‘prefer’, which make the process easier and smoother.

• A high contrast point
• Avoiding motion blur
• Avoiding harsh changes in light or colour (using led lights helps as they are more consistent)
• The tracking point to always be visible

 

2D vs 3D Motion Tracking

 

2D –

To track position is one point tracking

To track scale and/or rotation is two-point tracking

Data is needed only for an X, Y coordinate

 

3D –

At least a dozen tracking points are needed in order to track the motion of a camera in a 3D space

 

2D Tracking Position Demo

1.  In After Effects, bring in the footage by importing it into the project box. In our case, the footage was a motion tracking asset, a video of an android phone with a green screen and markers.
2.  Drag the footage over the coloured shaped button and make a new composition (puts the footage on the timeline).
3.  With the layer selected, go to the right panel in tracker and click track motion.
4.  A tracking point appears, with a small cross in the centre (centre position), a box (where we appoint which pattern to look for) and a bigger box (searches the area and looks for that pattern). As this has happened, a separate layer has been created, which can be seen at the top. One is with just the footage, and the other has the footage and the tracking point.

 

 

 

1.  Click the centre position to move the tracking point and place it on top of one of the markers (in our case this was the top left). A zoomed up box appears to allow you to be more specific.
2.  Firstly, scale up the search area (bigger box) to create a buffer zone around the marker. Ideally, this should be big enough that the marker is inside it at all times, even when moving.
3.  With the smaller box, scale it up just to the very edges of the marker.
4.  Go to analyze and click the play button to play the footage forward and track the marker. The square is the stop button but ESC also works.
5.  If the tracker loses the position of the marker, go back and adjust it. Re-record and it will track better.
6.  Once the tracking is complete for the whole video, go back to the other layer with just the footage (comp view) and bring in any image or text you would like.
7.  Again, switch to the other layer. Go to edit target on the right. Clicking that will specify the motion target. Press apply and ok and the image or text is then tracked to that position.

 

 

 

 

 

2D Tracking Rotation and Scale Demo

1.  In the layer with the tracking point, the track type is only position at the minute. Tick the box for scale and rotation. This makes another tracking point and a line, the latter being that which records scale and rotation.
2.  Move the second box to another marker and click the play button to track it.
3.  Like before, if the tracker loses the position of the marker, manually move it frame by frame as it is supposed to be. Sometimes, this means having to guess where the point is, like in our case, where the thumb covered the marker for a second or two and the tracker went a bit haywire. I went back and for every link that was out of place, I selected and moved the entire tracker back.
4.  Again like last time, an image can be imported or some text will do as well. In the tracker’s layer, click edit target and select the new asset. Click apply and ok.
5.  This time, I wanted the image to cover the entire screen of the phone. So, in the original layer (comp view), I adjusted and enlarged the image as best as I can to fit the phone. Usually, though, this isn’t accurate enough, in which case you go into the image layer, click layer, effect, distort, and corner pin, which allows you to fit the image to the phone by moving the pins to the corners of the screen.

 

 

3D Tracking Demo

1.  Import all the assets into After Effects.
2.  With the video layer selected, click effect, perspective, and 3D camera tracker, which tracks the footage for us.
3.  Some coloured banners will appear on the screen, one of them is ‘analyzing’ and the other is ‘solving’. Once there are finished, lots of dots will have appeared, which are actually all tracking points.
4.  Hovering over a point makes a red target appear. If you right-click on one and select create text & camera, the 3D camera tracker will be applied. This only needs to be done once but by hovering and right-clicking over other points, more text and solids can be added.

 

 

Personally, the 3D motion tracking was the most enjoyable one for this lesson, because the result was really cool and all I did was add some simple text! We didn’t have time to track the green screen drone footage into the scene but that would have looked awesome and I appreciate the fact that the process isn’t as complicated because the footage is automatically tracked.