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Forums Adobe After Effects Expressions Connecting movements inside of a mask to a slider

  • Connecting movements inside of a mask to a slider

  • Kamiar Babaei

    May 1, 2021 at 1:32 am

    Is it possible?

    PS:I know you can do this using red giants plugin or make anything react to music using convert Music to keyframes option.

  • Kamiar Babaei

    May 1, 2021 at 5:29 pm


  • Dan Ebberts

    May 1, 2021 at 10:44 pm

    You could set up an expression for your mask path, where the height is based on the slider value. This example is more complicated than it needs to be, because I wasn’t sure whether your path goes clockwise or counter-clockwise so the expression allows for either:

    s = effect("Slider Control")("Slider");

    p = thisProperty.points();

    if (p[1][0] < p[3][0]){

    p0 = p[3] - [0,s];

    p1 = p[2] - [0,s];

    newP = [p0,p1,p[2],p[3]];


    p0 = p[1] - [0,s];

    p3 = p[2] - [0,s];

    newP = [p0,p[1],p[2],p3];



  • Kamiar Babaei

    May 2, 2021 at 9:38 am

    Thank you so much for this awesome expression.

    But what i meant was the white bar inside of the mask is going to move vertically and i need the slider to acknowledge it and set a value to it between 0-100 based of the size of the mask.

    is it possible?

    thank you so much and sorry for not explaining properly what i wanted at first, i didn’t how to say it.

  • Dan Ebberts

    May 3, 2021 at 10:09 pm

    The only thing I can think of would be to use sampleImage() (with postEffect=true) in a loop, starting at the top of the range and moving down (1 pixel at a time) until you find a pixel with non-zero alpha to determine the current height of that bar. Then use that value to drive the height of the mask.

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