Count layers within precomposed layer

Great. That works.

Thnx again for your help Dan.

:F

Here is the working code.

It takes a selection of comps in the active comp.

Enables timeremapping.

Adds a null as controller with some sliders.

And adds an expression to the timeremapping

this just works with CompItems.

It is usefull if the layers in the comps are sequenced with one frame length

// written by fabiantheblind
// http://www.the-moron.net
// with a hint by Dan E.
// http://forums.adobe.com/message/3310628#3310628

applyExpression ();

function applyExpression(){

    // begin an Undo group
    app.beginUndoGroup("apply Expressions");
   
   
    // check if a comp is active
        var curComp = app.project.activeItem;
    if (!curComp || !(curComp instanceof CompItem))
    {
        alert("Please select a Composition.");
        return;
    }

    // get the selection
    var theSelection = curComp.selectedLayers;
   
    // you could use this for a null within the workarea
    //var theController = curComp.addNull(curComp.workAreaDuration);
   
    // add a null object to the comp for the slider controls
    var theController = curComp.layers.addNull();

    // make a unique name for the null. dont use the date its just a reminder
    theController.name =  prompt("Enter an unique name for the controller Null Object", "control_"+ Date().toString());

    // loop thru selection
    for (var layerId = 0; layerId < theSelection.length; layerId++)
    {
   
       
        var layer = theSelection[layerId];

        // get the number of layers within the layer
        // -1 because
        // layers start at index 1 frames start at 0 Frames
        // Thnx Dan for the word ".source."
        var theNumber = parseInt(layer.source.numLayers -1);

        // add a slider control to the null obj.
        var theSliderEffect = theController("ADBE Effect Parade").addProperty("ADBE Slider Control");
       
        // change the name of the slider to something usefull
        theSliderEffect.name = layer.name + "_cntrl_" + layerId;
       
        // this is for the timeremapping to make em all hold keyframes
        var holdInt = KeyframeInterpolationType.HOLD;
        // get the timeremapping property and enable it
        var property = layer.property("ADBE Time Remapping");
              layer.timeRemapEnabled = true;
            // set all keyframes to hold
      for (var i = 1; i <= property.numKeys; i++){
        property.setInterpolationTypeAtKey(i, holdInt, holdInt);
        }
        // remove the last keyframe. dont need it
        property.removeKey(property.numKeys);
        // check if the property can take expressions
        // dont need it. but i need more checking
        if (!property.canSetExpression) { continue }
       
        // apply the expression with
        //the name of the slider
        // the name of the control null
        // and the number of layers within the comps
        property.expression = exprString(theSliderEffect.name, theController.name, theNumber);
    }

    app.endUndoGroup();

    }

// this function builds the expression string
function exprString(inEffName, inControllerName,inNum){
   
    // the name of the effect
    var theEffName =  inEffName;
    // the name of the control null obj
    var theCntrlName = inControllerName;
    // the number of layers within the timeremapped comps
    var theNumber = inNum;
   
   
   
    // the expr will be something like this: !!watch out german expression!! (replace "Schieberegler" with "Slider Control"):
    // this expression remaps the frame number within the comp to values from the slider
    // val = Math.floor(thisComp.layer("control").effect("MovementControl")("Schieberegler"))*thisComp.frameDuration;
    //if (Math.floor(thisComp.layer("control").effect("MovementControl")("Schieberegler")) < 0){val =0;
    //}if (Math.floor(thisComp.layer("control").effect("MovementControl")("Schieberegler")) > 3){val =3* thisComp.frameDuration;
    //}

   
    // build the string with the variables from the selection
    var theString = "val = Math.floor(thisComp.layer(\"" + theCntrlName + "\").effect(\"" + theEffName +"\")(\"Schieberegler\"))*thisComp.frameDuration;\n"+
    " if (Math.floor(thisComp.layer(\"" + theCntrlName + "\").effect(\""+ theEffName +"\")(\"Schieberegler\")) < 0){val =0;\n"+
    " }if (Math.floor(thisComp.layer(\"" + theCntrlName + "\").effect(\""+ theEffName +"\")(\"Schieberegler\")) > "+theNumber+"){val ="+theNumber+"* thisComp.frameDuration;\n }" ;
   
    // and return the string
    return theString;
}