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:
- Each layer has it's own set of properties. Any change to a layer property applies only to the selected layer. You can view all of a layer's properties by clicking on the small triangle next to the layer name in the timeline. You can also access individual properties using the appropriate keyboard shortcuts.
- Motion is created by changing properties over time. To change a property over time you need to set keyframes for that property.
- Keyframes must be 'turned on' for each individual layer and property. You turn keyframes on by clicking the stopwatch icon next to the property name in the timeline. Once you have turned on keyframes for a property you do not need to click the stopwatch icon again. New keyframes will be generated automatically each time you change the property.
- Again, to create motion you need to change a property over time. This means you need a minimum of 2 keyframes in order to create motion. Speed is a property of time and distance, so it will be affected by both how far apart the keyframes are in time and how much change (in position, rotation, etc) occurs between the two 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:
- Once you turn keyframes on for a property, any change you make to that property will automatically create a new keyframe. However, there may be times when you want to add a keyframe without changing the property, for instance when you want an object to stop moving briefly. To do this, simply check the keyframe box on the far left of the timeline next to the property you are working with.
The keyframe box may have small black arrows on either side of it. These arrows are shortcuts which allow you to jump the playhead to the next or previous keyframe. If you need to change a value at a keyframe, this is a much more precise way of selecting the keyframe than simply moving the playhead until it lines up with the keyframe.
- You can also jump to the next or previous visible keyframe using the 'j'(previous) or 'k'(next) keyboard shortcuts. These will jump to the next or previous visible keyframe regardless of which layer or property it is on.
- You can move a keyframe to a different time simply by selecting it and dragging it to the left or right. To move more than one keyframe at a time, click somewhere near the first keyframe and drag a selection box across all the keyframes you want to select, or, shift-click to select multiple keyframes. Once they are highlighted, drag any of the selected keyframes to a new time and they will all move together.
- To eliminate a keyframe, select it and press the delete key. If you select multiple keyframes using the click-and-drag technique above, you can then remove all selected keyframes at once with the delete key.
- You can copy and paste keyframes fairly easily. Select the keyframes you want to copy, choose Edit>Copy or press Apple-C to copy. Then move the playhead to another time where you want to paste the keyframes and select Edit>Paste or press Apple-P. The keyframes you copied should appear at the new time. If you want to paste keyframes from one layer to another, after you copy select the layer you want to past to before pasting.
Keyframe InterpolationAfter 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 KeyframesBy 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:
- Menu - select the keyframe you want to hold and from the main menu choose Animation>Toggle Hold Keyframe.
- Keyboard Shortcut - select the keyframe you want to hold and press apple-option-H
- Contextual Menu - Right-click or Control-click on a keyframe and from the contextual menu that pops up choose "Toggle Hold Keyframe".
Linear InterpolationWhen 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:
- Menu - select the keyframe you want change and from the main menu choose Animation>Keyframe Interpolation...
- Keyboard Shortcut - select the keyframe you want to change and press apple-option-K
- Contextual Menu - Right-click or Control-click on a keyframe and from the contextual menu that pops up choose "Keyframe Interpolation..."
Roving KeyframesWhen 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.