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Properties and Keyframe


First off, I just want to review some of the important points to remember from last week's introduction to properties and keyframes:

Working with Properties

Using the keyboard shortcuts is a good way to view one property at a time. Sometimes, however, you may want to see more than one property, but not all of them, and you can still do this with keyboard shortcuts. First use the normal shortcut to show the first property you wish to view. For instance, press the "P" key to view the position property. Then hold the shift key while you press the shortcut for the second property. So if you now hit "Shift-R" rotation will drop down in addition to position. This way you can view any combination of properties for a layer that you like.

The keyboard shortcut "u" will show all of a layer's properties which have keyframes on them.

Working with Keyframes

There are a few basics of working with keyframes that you need to know:

Keyframe Interpolation

After Effects can Interpolate motion through keyframes in a variety of different ways. I'm not going to cover all the different options at this point but I wanted to point out a few that are pretty straightforward (and useful):

Hold Keyframes

By default AE always transitions smoothly from one keyframe setting to the next - but sometimes this isn't what you want. Making a keyframe a Hold keyframe will hold it's value until the next keyframe - and then immediately jump to the next keyframes value. There are several ways to turn a keyframe into a hold keyframe: To change a hold keyframe back to a normal interpolation just select the hold keyframe and repeat one of the above commands to toggle it back.

Linear Interpolation

When creating a motion path through a series of keyframes, AE defaults to an interpolation method called "Auto Bezier" which creates a smooth, curved path through all of the keyframes. Usually this is fine but there can be situations where you want the motion path to make hard angles instead of smooth curves when it changes direction.

Linear Interpolation gets rid of the curve in the path through a keyframe. This can be set through the Keyframe Interpolation dialogue which can be accessed in several ways:

Any of these three options will bring up the following dialogue box: From the drop-down menu next to "Spatial Interpolation" choose "Linear", click "OK" and the motion path in your canvas window will change to reflect the new setting (the path should make a hard angle through the keyframe you changed).

To change it back, repeat the procedure and change the "Spatial Interpolation" setting back to "Auto Bezier".

Roving Keyframes

When you create a complex motion path it can be difficult to maintain a smooth, steady rate of speed throughout the path. Unless you are very careful the velocity will change between each pair of keyframes and you will see the layer speed up and slow down as it enters/exits each keyframe.

Roving Keyframes allow the keyframes to change their position in time automatically to maintain a steady velocity throughout all of them. You cannot set the first or last keyframe on a property to rove - these are the one's that determine the timing of all the rest. However you can have one or all of the other keyframes rove to smooth things out.

Roving is set in the same dialogue box as Linear Interpolation (above). Select one or more keyframes and use one of the methods listed above to open the Keyframe Interpolation dialogue. Under the "Roving" option change the drop down menu from "Lock To Time" to "Rove Across Time". Click "OK" and the keyframes will change from diamond shape to very small circles. They will also automatically distribute themselves on the timeline to maintain a constant velocity.

Try dragging one of the non-roving keyframes on either side of the roving ones to a new time - the roving frames will continuously adjust themselves to maintain a consistent velocity.

These cover most of the things you will commonly to do with keyframes. There are some more advanced methods for changing the speed and motion through the keyframes which we'll will cover later in the semester - see my notes on Property Graphs if you are interested in reading ahead.