<span id="duration">--:--</span>
                <button onclick="audio.loop = !audio.loop">loop</button>
                <button onclick="audio.playbackRate = -audio.playbackRate">reverse</button>
                <span id="duration">--:--</span>
                <button onclick="audio.loop = !audio.loop">loop</button>
                <button onclick="audio.playbackRate = -audio.playbackRate">reverse</button>