如何为iframe音频制作播放/停止按钮？

<iframe src="audio.html"></iframe>

<audio id="audio" src="audio.mp3"></audio>
<button id="playButton">播放</button>
<button id="stopButton">停止</button>

var playButton = document.getElementById('playButton');
var stopButton = document.getElementById('stopButton');
var audio = document.getElementById('audio');

playButton.addEventListener('click', function() {
  audio.play();
});

stopButton.addEventListener('click', function() {
  audio.pause();
  audio.currentTime = 0;
});