利用<audio> 元素的timeupdate 事件（每秒触发三到四次）通过检查.currentTime 的<audio> 元素在媒体流期间执行精确的动画。每秒最多可以启动或停止几次动画或过渡。
如果在浏览器可用，您可以使用fetch() 请求音频资源，在.then() 返回response.body.getReader()，它返回资源的ReadableStream；创建一个新的MediaSource 对象，将MediaSource 的<audio> 或new Audio() .src 设置为objectURL；将.read()处的第一个流块附加到MediaSource的.then()链接sourceBuffer，.mode设置为"sequence"；在 sourceBuffer updateend events 处将剩余的块附加到 sourceBuffer。
如果fetch() response.body.getReader() 在浏览器中不可用，您仍然可以使用<audio> 元素的timeupdate 或progress 事件来检查.currentTime，在流式传输所需的第二秒开始或停止动画或过渡媒体播放。
当流在MediaSource 累积足够的缓冲区以继续播放时，使用<audio> 元素的canplay 事件播放媒体。
您可以使用属性设置为对应于应发生动画的<audio> 的.currentTime 的数字的对象，并将值设置为应设置动画以执行精确动画的元素的css 属性。
在下面的javascript，动画每二十秒出现一次，从0开始，每六十秒出现一次，直到媒体播放结束。
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta charset="utf-8" />
<title></title>
<style>
body {
width: 90vw;
height: 90vh;
background: #000;
transition: background 1s;
}
span {
font-family: Georgia;
font-size: 36px;
opacity: 0;
}
</style>
</head>
<body>
<audio controls></audio>
<br>
<span></span>
<script type="text/javascript">
window.onload = function() {
var url = "/path/to/audio";
// given 240 seconds total duration of audio
// 240/12 = 20
// properties correspond to `<audio>` `.currentTime`,
// values correspond to color to set at element
var colors = {
0: "red",
20: "blue",
40: "green",
60: "yellow",
80: "orange",
100: "purple",
120: "violet",
140: "brown",
160: "tan",
180: "gold",
200: "sienna",
220: "skyblue"
};
var body = document.querySelector("body");
var mediaSource = new MediaSource;
var audio = document.querySelector("audio");
var span = document.querySelector("span");
var color = window.getComputedStyle(body)
.getPropertyValue("background-color");
//console.log(mediaSource.readyState); // closed
var mimecodec = "audio/mpeg";
audio.oncanplay = function() {
this.play();
}
audio.ontimeupdate = function() {
// 240/12 = 20
var curr = Math.round(this.currentTime);
if (colors.hasOwnProperty(curr)) {
// set `color` to `colors[curr]`
color = colors[curr]
}
// animate `<span>` every 60 seconds
if (curr % 60 === 0 && span.innerHTML === "") {
var t = curr / 60;
span.innerHTML = t + " minute" + (t === 1 ? "" : "s")
+ " of " + Math.round(this.duration) / 60
+ " minutes of audio";
span.animate([{
opacity: 0
}, {
opacity: 1
}, {
opacity: 0
}], {
duration: 2500,
iterations: 1
})
.onfinish = function() {
span.innerHTML = ""
}
}
// change `background-color` of `body` every 20 seconds
body.style.backgroundColor = color;
console.log("current time:", curr
, "current background color:", color
, "duration:", this.duration);
}
// set `<audio>` `.src` to `mediaSource`
audio.src = URL.createObjectURL(mediaSource);
mediaSource.addEventListener("sourceopen", sourceOpen);
function sourceOpen(event) {
// if the media type is supported by `mediaSource`
// fetch resource, begin stream read,
// append stream to `sourceBuffer`
if (MediaSource.isTypeSupported(mimecodec)) {
var sourceBuffer = mediaSource.addSourceBuffer(mimecodec);
// set `sourceBuffer` `.mode` to `"sequence"`
sourceBuffer.mode = "sequence";
fetch(url)
// return `ReadableStream` of `response`
.then(response => response.body.getReader())
.then(reader => {
var processStream = (data) => {
if (data.done) {
return;
}
// append chunk of stream to `sourceBuffer`
sourceBuffer.appendBuffer(data.value);
}
// at `sourceBuffer` `updateend` call `reader.read()`,
// to read next chunk of stream, append chunk to
// `sourceBuffer`
sourceBuffer.addEventListener("updateend", function() {
reader.read().then(processStream);
});
// start processing stream
reader.read().then(processStream);
// do stuff `reader` is closed,
// read of stream is complete
return reader.closed.then(() => {
// signal end of stream to `mediaSource`
mediaSource.endOfStream();
return mediaSource.readyState;
})
})
// do stuff when `reader.closed`, `mediaSource` stream ended
.then(msg => console.log(msg))
}
// if `mimecodec` is not supported by `MediaSource`
else {
alert(mimecodec + " not supported");
}
};
}
</script>
</body>
</html>
plnkrhttp://plnkr.co/edit/fIm1Qp?p=preview