function playVideo(elementId) {
    var element = document.getElementById(elementId);
    
    element.style.visibility = "visible";
    element.style.opacity = "100%";
    element.play();
}

function stopVideo(elementId) {
    var element = document.getElementById(elementId);
    
    element.style.visibility = "hidden";
    element.style.opacity = "0%";
    element.pause();
    element.currentTime = 0;
}