Setting up an expression in After Effects to automatically fade in and out a layer can be cost-effective over time, since you’ll be able to adjust both its start and end times without having to adjust keyframes separately.
Start by creating an expression on your layer’s Opacity keyframe and setting an expression variable for its duration; once created, this time can easily be altered later if required – for instance by setting variable and editing expression at run time, as follows.
Fade Time =.33 This value represents one-third of a second or approximately 10 frames from 29.97 composition.
Create a variable for the fade in and use the linear expression as one of my previous tutorials discussed it; its written form can be found here:
Linear(var, varMin, varMax, value1, value2)
As we’re dealing with when layers begin, the variable time will become relevant here. VarMin represents exactly the moment the layer starts – in Point format; VarMax represents when fading should end (in Point+fadeTime that we set earlier); Finally value1 and 100 represent starting and ending opacities respectively.
Written out, the name appears as:
fadeIn(time, inPoint, fadeTime);
Next, we create a variable for fade out by using another linear expression involving outPoint as the target out point for our layer’s out point and outPoint-fadeTime as its starting point (written out: outPoint-fadeTime). Here’s an example:
FadeOut = linear(time,outPoint-fadeTime, 100);
Finally, we combine both results to get our output:
fadeIn-FadeOut;
This expression looks as follows:
fadeIn is determined using linear integration and hashing; fadeTime=0.033 and fadeIn should equal 100;
Fade Out = linear(Time, OutPoint-fadeTime, 100);
FadeIn-fadeOut; To customize the length of your fade, change the numeric value.33 as desired. You can alter layer starting/ending points as necessary with ease, with expression adapting accordingly and keeping its fade in sync.
