public void setSpeed(double speed) {
        this.speed = speed;
        if (speed < 0) {
            setForward(false);
        } else {
            setForward(true);
        }
    }
Alters the speedup factor applied by the layer running this action.
<p>
Notes:
<li> This factor controls the animation direction, if the speed is a positive value then the animation will run forward and vice versa. </li>
<li> The speed factor gets applied, inside the {@link com.jme3.anim.AnimLayer}, on each interpolation step by this formula : time += tpf * action.getSpeed() * composer.globalSpeed. </li>
<li> Default speed is 1.0, it plays the animation clips at their normal speed. </li>
<li> Setting the speed factor to Zero will stop the animation, while setting it to a negative number will play the animation in a backward fashion. </li>
</p>

@param speed the speed of frames.
jme3-core/src/main/java/com/jme3/anim/tween/action/Action.java