レイヤーの不透明度に適用
inPoint、outPointを変えてもフェード時間は変わらなくなる
fadeInDuration = 0.5;
fadeOutDuration = 0.5;
if(time<(inPoint+fadeInDuration)){
linear(time, inPoint, inPoint+fadeInDuration, 0, 100);
}else{
linear(time, outPoint - fadeOutDuration, outPoint, 100, 0);
}