protected void setFirstActiveIndex(int index) {
        this.firstActiveIndex = index;
    }
BlendAction will stretch it's child actions if they don't have the same length.
This might cause stretched animations to run slowly. This method generates factors
based on how much actions are stretched. Multiplying this factor to base speed will
resolve the slow-motion side effect caused by stretching. BlendAction will use the
blend weight taken from BlendSpace to interpolate the speed factor for current frame.
jme3-core/src/main/java/com/jme3/anim/tween/action/BlendAction.java