There are two buttons in the audio player code: start and stop. These two functions are required to work on a single button on a click. Preferably with the corresponding icon change.
<audio id='player' src='http://retroserver.streamr.ru:8040/radio7128.mp3'/> <button onclick='document.getElementById('player').play()'><font size='+1'><i aria-hidden='true' class='fa fa-play'/></font></button> <button onclick='document.getElementById('player').pause()'><font size='+1'><i aria-hidden='true' class='fa fa-stop'/></font></button> <button onclick='document.getElementById('player').volume+=0.1'><font size='+2'><i aria-hidden='true' class='fa fa-volume-up'/></font></button> <button onclick='document.getElementById("player").volume=Math.max(document.getElementById("player").volume - 0.1, 0)'><font size='+2'><i aria-hidden='true' class='fa fa-volume-down'/></font></button>