After Effects Expression

Moving position upward and downward
//350 is 350px
//3 is speed


posY = 540;
posX = 960;
posY = posY +  Math.sin(time*3) * 350;
[posX,posY]

////////////////////////////
Default position

x = transform.position[0];
y = transform.position[1];

////////////////////////////
To start an expression at the specific time

timeStart = 4;	//start at 4 sec
if(time>timeStart){
//insert your expression here
}else{
//do nothing,but make sure there is a returned result
}

////////////////////////////

+---[ SHAPE LAYER AUTO-FIT TEXT WIDTH ]----------------------------+
|
| [ Shape Layer > Transform > Position ]
|
	t = thisComp.layer("my_text");
	tRect = t.sourceRectAtTime(time,false);
	tUL = t.toComp([tRect.left,tRect.top]);
	tLR = t.toComp([tRect.left+tRect.width,tRect.top+tRect.height]);
	tCenter = (tUL + tLR)/2
	myRect = sourceRectAtTime(time,false);
	myUL = toComp([myRect.left,myRect.top]);
	myLR = toComp([myRect.left+myRect.width,myRect.top+myRect.height]);
	myCenter = (myUL + myLR)/2
	delta = myCenter - tCenter;
	value - delta

| [ Shape Layer > Rectangle 1 > Scale ]
|
	t = thisComp.layer("my_text");
	tRect = t.sourceRectAtTime(time,false);
	tUL = t.toComp([tRect.left,tRect.top]);
	tLR = t.toComp([tRect.left+tRect.width,tRect.top+tRect.height]);
	myRect = sourceRectAtTime(time,false);
	myUL = toComp([myRect.left,myRect.top]);
	myLR = toComp([myRect.left+myRect.width,myRect.top+myRect.height]);
	margin = 10;
	[(tLR[0]-tUL[0] + 2*margin)/(myLR[0]-myUL[0]),(tLR[1]-tUL[1]+ 2*margin)/(myLR[1]-myUL[1])]*100

+--------------------------------------------------------------------------------------------------------+


http://youtube.com/ShuichiSyad