Stabilize a Moving Shot

Stabilize a Moving Shot

After Effects doesn’t provide you with a workfl ow to take
a shot with a moving camera—handheld, aerial, crane, or
dolly—and smooth bumps in the motion while retaining
the move. But you can do it.
 features an aerial shot of Silicon Valley (look
closely and you’ll see Adobe headquarters). It wasn’t taken
in a helicopter with a gyro, but rather from a camera
attached to a 2 × 4 wooden plank, C-clamped to the open
door of a Cessna aircraft. The pilot did his best to keep the
plane steady, but even on a calm day that type of aircraft
bobs and weaves, which is why you might pay ten times
more money to get the helicopter with the gyro.

Ah, but it’s so much fun to fi x it in post. To stabilize a shot
like this, fi rst decide where the viewer’s attention will be,
because that’s the area that you want to stabilize. Objects in
the near foreground move more than those in the distance;
stabilizing them adds motion on the horizon. In this
case, the viewer’s attention is likely on the near-horizon,
below the foothills. Begin by creating a Position/Rotation/
Scale stabilization based on two points at that depth.
The basic setup replicates the fi rst four steps from the last
section, but instead of parenting the camera to the stabilized
source layer, follow these steps:
1. Create a null named Stabilizer (or your choice), and
enable 3D.
2. Select all of the Anchor Point keyframes from the stabilized
background plate.
3. Copy and paste the Anchor Point keyframe data to
Stabilizer.
4. Apply smoothing to this duplicated smoothing data.
5. Parent the camera to the Stabilizer layer (Figure 8.18).
You have a couple of options to “apply smoothing”:
Window > Smoother is an automatic but destructive solution;
the smooth() expression is a vastly superior technique,
because you can view the smoothed motion in the Graph
Editor without affecting the source keyframes. If, later on, it
turns out you need to adjust it again.


To apply a smooth() expression
1. Alt/Option-click on the Anchor Point stopwatch of the
layer to which the camera is parented.
2. With the default expression (anchorPoint) still highlighted,
go to the Expressions menu icon and
under Property choose the smooth default:
smooth(width = .2, samples = 5, t = time).
This works, but as a starting setting, I recommend discarding
the third argument (“t = time”) and the other
hints (“width =” and “samples =”) to get the leaner,
meaner and more powerful setting like smooth(2, 48).
The expression works as follows: It gives a command
(smooth()) followed by three settings known as arguments.
The third one, time, is used only to offset the result, and
it’s optional, so I have a habit of deleting it. The hints
for the other two (width = and samples =) are also not
needed to make the expression work—they are there just
to remind you what they do.
Width determines how much time (before and after the
current time) is averaged to create the result. A setting of
2 samples 2 seconds means 1 second before and 1 second
after the current time. The samples argument determines
how many individual points within that range are actually
sampled for the result; generally, the more samples, the
smoother the curve. A setting of 48 means that over that 2
seconds, 48 individual frame values will be averaged (the
maximum for 24 fps footage).
It’s also possible to smooth rotation in this manner,
although I fi nd a lighter touch (fewer samples) works best
with rotation. However, the best way to fi nd out for your
individual shot is by trying different settings, looking at
how smooth the resulting curve (not to mention the actual
motion) appears.
It’s a little hard to imagine that you can smooth the motion
data for the camera, causing it to go out of sync with the
background, and not have a mismatch. What is actually
happening, though, is that the scene motion is removed
completely and then restored in a smoother state.