ENTER_FRAME event produces choppy video scrubbing

programming flash
1

This code works fine if the timeline is moving forward through the .flv file. However, the going in reverse produces choppy results. The choppyness seems uniform, as in, it’s always choppy and always the same intensity. So I don’t think it’s a computer issue, rather a code issue?

addEventListener(Event.ENTER_FRAME, smoothMove);  
function smoothMove(event:Event) { 

    if (smoothZUp == true) {
        btn8.y = btn8.y - 1;
        dockVid.gotoAndStop(dockVid.currentFrame + 1);
        
    } else if (smoothZDown == true) {
        btn8.y = btn8.y + 1;
        dockVid.gotoAndStop(dockVid.currentFrame - 1);
        
    } else {
        //do nothing
    }
}