[Dan Ebberts]

Assuming you put the checkboxes on the Scene precomp layers, this is how I’d do it:

audioOn = -22;
audioOff = -6;
fadeFrames = 10;
fadeTime = framesToTime(fadeFrames);
v = audioOff;
for (i = 1; i <= thisComp.numLayers; i++){
  myLayer = thisComp.layer(i);
  if (myLayer.index == index) continue;
  if (myLayer.name.indexOf("Scene") == 0 && time >= myLayer.inPoint && time <= myLayer.outPoint){
    if (myLayer.effect("On")("Checkbox") == 1){
      if (time < (myLayer.inPoint + myLayer.outPoint)/2){
        v = linear(time,myLayer.inPoint,myLayer.inPoint + fadeTime,audioOff,audioOn);
      }else{
        v = linear(time,myLayer.outPoint - fadeTime,myLayer.outPoint,audioOn,audioOff);
      }
    }
    break;
  }
}
[v,v]

[Dan Ebberts]

That seems pretty complex. Can you describe the set up a little? Do your scenes ever overlap? Does the checkbox need to be inside the scene comp, or could it be on the precomp layer so the expression doesn’t need to dig into the precomp to get it? From looking at the code, it looks like the precomp layers don’t have the same names as the precomps themselves, is that correct?

[Dan Ebberts]

For example, this simple time remapping expression will hold a clip at frame 0 until the clip’s first marker is reached. The clip then plays from the marker onward.

t = 0;
if (marker.numKeys > 0){
  t = time - marker.key(1).time;
}

[Dan Ebberts]

Expressions can’t move a clip, but if you turn on time remapping for the clip, a time remapping expression can determine when it plays.

[Dan Ebberts]

<div>>Maybe an array or something?</div>

Yes, try it this way:

[wiggle(10,5)[0], value[1]]

[Dan Ebberts]

s -= l.startTime;

is equivalent to this:

s = s - l.startTime;

[Dan Ebberts]

It just subtracts the layer’s start time from the marker time, to compensate for the layer not starting at time = 0.

[Dan Ebberts]

If you create a type-on effect with a source text expression like this:

rate = 20;
value.substr(0,time*rate)

then

yourTextLayer.sourceRectAtTime(time,false)

will give you accurate results.

[Dan Ebberts]

Once you’ve capture the selected layers into myLayers, I think you need to deselect them all, so that only one property at a time is selected:

function addKeys(){
	var myComp = app.project.activeItem;
	var myLayers = myComp.selectedLayers;
	if (myLayers.length > 0){
		var myLayer = myLayers[0];
		for (var i = 0; i < myLayers.length; i++){
			myLayers[i].selected = false;
		}
		for (var i = 0; i < myLayers.length; i++){
			try{		       
				var myProp = myLayers[i].effect("Opacity Controller")("Opacity Offset");
				myProp.expressionEnabled = true;
				myProp.selected = true;
				app.executeCommand(app.findMenuCommandId("Convert Expression to Keyframes"));
			}catch(err){			}
			myLayers[i].selected = false;
		}
	}
}

[Dan Ebberts]

Just a hunch that the ones that don’t work also don’t start at time=0 in the “footage strip” comp.

If that’s the case, try this:

c=comp("footage strip");
l= c.layer(thisComp.name);
s=l.marker.key(1).time;
d=comp("footage strip").layer("xp").effect("fd")("Slider");
s -= l.startTime;
ease(time,s,(s+d),0,100);