My understanding right now is that there probably isn't a "create" method for creating shapes or objects in expressions. Please correct me if I'm wrong.

Instead I should create my shape and then use expressions for duplicating that layer while repositioning it. Does this sound like the correct method?

It would make sense that a keyframe couldn't hold an object. On the other hand it seems you could easily end up with a trillion layers in a comp..

Hi Dan,

afraid that only shows my unfamilarity with AE. More used to 3D than 2,5D. So now I've found out that you can use the effect CC sphere and orient it towards the camera to make it look like 3D.

Let me see if I understand you correctly.

I have hundreds of keyframes with a single value in them. Then I use them to move a circle around the screen. But what if I would like to leave a copy of that circle everyplace it has been. Are my only options to either manually create lots of layers or do that with a script. No easier way?

Oh, thank you. The keyframes only hold a single value so I already have an expression for the position. So the keyframes are in a separate layer.

x=time*20;

note=thisComp.layer("midi").effect("ch_0_pitch")("Slider"); //this is the keyframes

y=linear(note, 60, 74, 0, -100);

centre=[50, 180, 0];

add(centre,[x,y]);

Spot on. No need to change even a comma.

This is how it looks: (click on the images to see the animation)

But I guess to make those new layers do something, stay around for a while, scale etc for longer than until the next keyframe I need to give them their own keyframes. Something like this:

But I cant do that manually, I would like to use it for visualizing a song and it would take thousands of keyframes. Maybe someday I can learn to write scripts...

In a project trying to visualize Pachelbels Canon in D I'm also using David van Brinks midi-script and found the same need to transform expressions to keyframes.

Here's the beginning of the song: http://www.screencast.com/t/eAWWQtGQp

It's very simple to make the green sphere jump, just setting the keyframes in the midi-layer to hold. And the other frames to bezier (or linear, in this case it wont make a difference). But towards the end when I want the blue sphere to start bouncing I found it needed its own keyframes. So I used "Convert expression to keyframes". The problem is that it creates keyframes on every frame and I must have keyframes only where the midi-keyframes are (which often don't even line up with the start of a frame).

But some day in a far distance maybe I can write a script that creates only those keyframes that I need.

David pointed me out where in the script I should start looking for a way to do this. I haven't done any scripting in AE before, but will give it a try.