After Effects Expressions

autoFadeEase.jsx

//Autofade: Add to opacity
// If there are two markers on the layer, then they are used to set the duration; otherwise, a default value is used.
transition = 15;       // transition time in frames
var v = transform.opacity;
if (marker.numKeys<2){
tSecs = transition / ( 1 / thisComp.frameDuration); // convert to seconds
ease(time, inPoint, inPoint + tSecs, 0, v) - ease(time, outPoint - tSecs, outPoint, 0, v)
}else{
ease(time, inPoint, marker.key(1).time, 0, v) - ease(time, marker.key(2).time, outPoint, 0, v)
}

autoFadeLinear.jsx

//Autofade: Add to opacity
// If there are two markers on the layer, then they are used to set the duration; otherwise, a default value is used.
//linear
transition = 15;       // transition time in frames
var v = transform.opacity;
if (marker.numKeys<2){
tSecs = transition / ( 1 / thisComp.frameDuration); // convert to seconds
linear(time, inPoint, inPoint + tSecs, 0, v) - linear(time, outPoint - tSecs, outPoint, 0, v)
}else{
linear(time, inPoint, marker.key(1).time, 0, v) - linear(time, marker.key(2).time, outPoint, 0, v)
}