After Effects: Increment a Variable over time

Question

I have following problem: I am trying to tweak the speed of a Math.sin function. Therefore I need a variable that incerements over time with a combination of a keyframed speed variable.

Sounds complicated, I know.

Let's say I am using the global time variable and convert it with the timeToFrames() function I get an integer value for each frame.

myTime = timeToFrames(time);

This leads me to a value of 1 for Frame 1, a value of 2 for Frame 2, and so on. But what if I want to manipulate the increment. For example:

//speed (gets tweened from a certain value range,for example: 10 - 1)
s = (some connected slider here)

myTime += s;

If I have a speed of 10 at Frame 1 I would get a value of 11. If I have a speed of 8 at Frame 2, I would expect a value of 11 + 2 + 8 = 21.

What I get is only 2 + 8;

So I need to store the value at every frame. Is this possible?

Please help.

Answer 1

You can loop over the range of frames from the start of the comp to the present and calculate the value along the way.

function myFuncf(theTime){
 //whatever the function you're using to create the value, e.g.
 t=theTime + s.valueAtTime(theTime); //s is the slider
 return t
}

firstFrame = timeToFrames(inPoint); //if you want it to calculate
                                    //from the beginning of the comp
                                    //change this to 0, or maybe 1?
                                    //I'd check but I'm rendering ATM

mytime=0; //initialise the mytime variable

currentFrame = timeToFrames(time);
for (int i=firstFrame; i <= currentFrame; i++){
  mytime += myFunc(framesToTime(i)); //need to convert frames back into seconds
}

after the loop myTime should be the sum of the results of function myFunc from all the previous frames up to and including the present one (I'm not 100% sure if the loop should end when i < cf or i <= cf, you might want to test).

note first time I posted this there was a mistake. Where I called the function I was giving it frames (from i the loop variable), but it uses valueAtTime which expects time in seconds, so you need to convert: mytime += myFunc(framesToTime(i));

If you have a long comp or this is applied to lots of layers, this expression may become slow to evaluate and cause lagginess. If it becomes a problem convert the expression to keyframes.

Answer 2

If anyone is still looking for a solution that wont blow up computation times, I found this workaround using environment variables which will store values outside of the script context.

The if statement will define the Env-Variable at frame 0 and afterwards increase and use the variable each frame. Note that x could be any value. In my case it was an audio amplitude effect slider value.

if ($.myEnvVariable == null){
    $.myEnvVariable = 0
} 
// x = value from slider
$.myEnvVariable = $.myEnvVariable + x
$.myEnvVariable