var v = $('#video_html5_api')[0];
var offsetTime = function (video, offset) {
    video.currentTime = (video.currentTime + offset);
};
var c = document.createElement('div');
c.style.position="absolute";
c.style.top="0";
c.style.right="0";
var createButton = function (video, label, offset) {
    var b = document.createElement("button");
    b.innerHTML = label;
    b.addEventListener('click', function(){
        offsetTime(video, offset);
    });
    return b;
};

document.body.appendChild(c);
c.appendChild(createButton(v, "-10m", 10 * -60));
c.appendChild(createButton(v, "-1m", 1 * -60));
c.appendChild(createButton(v, "-5s", -5));
c.appendChild(createButton(v, "5s", 5));
c.appendChild(createButton(v, "1m", 1 * 60));
c.appendChild(createButton(v, "10m", 10 * 60));