JavaScript 实现页面中录音功能

页面中实现录音需要使用浏览器提供的 MediaRecorder API，所以前提是需要浏览器支持 MediaStream Recording 相关的功能。

以下代码默认工作在 Chrome 环境中。

准备页面

首先准备一个页面，其中内容很简单，一个录音按钮，一个用于播放的 <audio> 标签。

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>audio record</title>
</head>
<body>
    <div class="app">
        <button class="record-btn">record</button>
        <audio controls class="audio-player"></audio>
    </div>
    <script src="./recorder.js"></script>
</body>
</html>

获取录音权限

因为录音需要使用设备的话筒，所以第一步应该是向用户索要录音的权限。这是通过 MediaDevices.getUserMedia()
来完成的，其用法为：

var promise = navigator.mediaDevices.getUserMedia(constraints);

其中 constraints 为需要获取的权限列表，这里只需要指定音频 audio 即可。

其返回是个 Promise，因为用户何时进行授权是不确定的。通过在 Promise 的回调中进行授权成功或失败的处理。

在使用前需要判断浏览器是否已经支持相应的 API，此时得到如下的代码：

if (navigator.mediaDevices.getUserMedia) {
  const constraints = { audio: true };
  navigator.mediaDevices.getUserMedia(constraints).then(
    stream => {
      console.log("授权成功！");
    },
    () => {
      console.error("授权失败！");
    }
  );
} else {
  console.error("浏览器不支持 getUserMedia");
}

其中成功回调里得到的入参 stream 为 MediaStream 对象。

此时运行后可看到浏览器展示出了让用户授权使用麦克风的提示。

向用户索要麦克风使用权限

创建录音实例

将上一步获取到的 MediaStream 传入 MediaRecorder 的构造器创建一个录音器的实例。

var mediaRecorder = new MediaRecorder(stream);

启动录音

通过监听页面中录音按钮的点击来启动录音。

const recordBtn = document.querySelector(".record-btn");
const mediaRecorder = new MediaRecorder(stream);
recordBtn.onclick = () => {
  mediaRecorder.start();
  console.log("录音中...");
};

MediaRecorder 实例上有个 state 状态，可用来判断录音器当前的活动状态，总共有三种值：

inactive：处于休息状态，要么是没开始，要么是开始后已经停止。
recording：录音中
paused：已经开始，但被暂停了，不是停止也没有被恢复。

所以通过这个状态，我们可以实现再次点击按钮时，结束录音。

recordBtn.onclick = () => {
  if (mediaRecorder.state === "recording") {
    mediaRecorder.stop();
    recordBtn.textContent = "record";
    console.log("录音结束");
  } else {
    mediaRecorder.start();
    console.log("录音中...");
    recordBtn.textContent = "stop";
  }
  console.log("录音器状态：", mediaRecorder.state);
};

音频数据的获取

上面按钮处理来自用户的交互，只负责启动或停止录音。音频的数据还是从 MediaRecorder 实例上通过监听其相应的事件来完成的。

当录音开始时，会触发其 MediaRecorder.ondataavailable 事件，从该事件回调的入参为 BlobEvent，从它身上取到 event.data 便是我们需要的音频数据。因为数据是一段一段产生的，所以需要暂存到一个数组中。

const chunks = [];
mediaRecorder.ondataavailable = function(e) {
  chunks.push(e.data);
};

目前为止完成的代码应该是这样的：

recorder.js

const recordBtn = document.querySelector(".record-btn");
const playBtn = document.querySelector(".play-btn");
if (navigator.mediaDevices.getUserMedia) {

var chunks = [];

const constraints = { audio: true };

navigator.mediaDevices.getUserMedia(constraints).then(

stream => {

console.log("授权成功！");
  <span class="pl-k">const</span> <span class="pl-c1">mediaRecorder</span> <span class="pl-k">=</span> <span class="pl-k">new</span> <span class="pl-en">MediaRecorder</span>(stream);

  <span class="pl-smi">recordBtn</span>.<span class="pl-en">onclick</span> <span class="pl-k">=</span> () <span class="pl-k">=&gt;</span> {
    <span class="pl-k">if</span> (<span class="pl-smi">mediaRecorder</span>.<span class="pl-smi">state</span> <span class="pl-k">===</span> <span class="pl-s"><span class="pl-pds">"</span>recording<span class="pl-pds">"</span></span>) {
      <span class="pl-smi">mediaRecorder</span>.<span class="pl-c1">stop</span>();
      <span class="pl-smi">recordBtn</span>.<span class="pl-smi">textContent</span> <span class="pl-k">=</span> <span class="pl-s"><span class="pl-pds">"</span>record<span class="pl-pds">"</span></span>;
      <span class="pl-en">console</span>.<span class="pl-c1">log</span>(<span class="pl-s"><span class="pl-pds">"</span>录音结束<span class="pl-pds">"</span></span>);
    } <span class="pl-k">else</span> {
      <span class="pl-smi">mediaRecorder</span>.<span class="pl-c1">start</span>();
      <span class="pl-en">console</span>.<span class="pl-c1">log</span>(<span class="pl-s"><span class="pl-pds">"</span>录音中...<span class="pl-pds">"</span></span>);
      <span class="pl-smi">recordBtn</span>.<span class="pl-smi">textContent</span> <span class="pl-k">=</span> <span class="pl-s"><span class="pl-pds">"</span>stop<span class="pl-pds">"</span></span>;
    }
    <span class="pl-en">console</span>.<span class="pl-c1">log</span>(<span class="pl-s"><span class="pl-pds">"</span>录音器状态：<span class="pl-pds">"</span></span>, <span class="pl-smi">mediaRecorder</span>.<span class="pl-smi">state</span>);
  };

  <span class="pl-smi">mediaRecorder</span>.<span class="pl-en">ondataavailable</span> <span class="pl-k">=</span> <span class="pl-k">function</span>(<span class="pl-smi">e</span>) {
    <span class="pl-smi">chunks</span>.<span class="pl-c1">push</span>(<span class="pl-smi">e</span>.<span class="pl-c1">data</span>);
  };
},
() <span class="pl-k">=&gt;</span> {
  <span class="pl-en">console</span>.<span class="pl-c1">error</span>(<span class="pl-s"><span class="pl-pds">"</span>授权失败！<span class="pl-pds">"</span></span>);
}

);

} else {

console.error("浏览器不支持 getUserMedia");

}

录音状态的查看

录音结束及音频的播放

通过监听 MediaRecorder.onstop 事件，将收集好的音频数据创建成 Blob 对象，然后通过 URL.createObjectURL 创建成 HTML 中 <audio> 标签可使用的资源链接。

mediaRecorder.onstop = e => {
  var blob = new Blob(chunks, { type: "audio/ogg; codecs=opus" });
  chunks = [];
  var audioURL = window.URL.createObjectURL(blob);
  audio.src = audioURL;
};

其中，在使用完收到到的音频数据后，将 chunks 置空方便下次录音时使用。

目前为止完成的代码应该是这样的：

recorder.js

const recordBtn = document.querySelector(".record-btn");
const player = document.querySelector(".audio-player");
if (navigator.mediaDevices.getUserMedia) {

var chunks = [];

const constraints = { audio: true };

navigator.mediaDevices.getUserMedia(constraints).then(

stream => {

console.log("授权成功！");
  <span class="pl-k">const</span> <span class="pl-c1">mediaRecorder</span> <span class="pl-k">=</span> <span class="pl-k">new</span> <span class="pl-en">MediaRecorder</span>(stream);

  <span class="pl-smi">recordBtn</span>.<span class="pl-en">onclick</span> <span class="pl-k">=</span> () <span class="pl-k">=&gt;</span> {
    <span class="pl-k">if</span> (<span class="pl-smi">mediaRecorder</span>.<span class="pl-smi">state</span> <span class="pl-k">===</span> <span class="pl-s"><span class="pl-pds">"</span>recording<span class="pl-pds">"</span></span>) {
      <span class="pl-smi">mediaRecorder</span>.<span class="pl-c1">stop</span>();
      <span class="pl-smi">recordBtn</span>.<span class="pl-smi">textContent</span> <span class="pl-k">=</span> <span class="pl-s"><span class="pl-pds">"</span>record<span class="pl-pds">"</span></span>;
      <span class="pl-en">console</span>.<span class="pl-c1">log</span>(<span class="pl-s"><span class="pl-pds">"</span>录音结束<span class="pl-pds">"</span></span>);
    } <span class="pl-k">else</span> {
      <span class="pl-smi">mediaRecorder</span>.<span class="pl-c1">start</span>();
      <span class="pl-en">console</span>.<span class="pl-c1">log</span>(<span class="pl-s"><span class="pl-pds">"</span>录音中...<span class="pl-pds">"</span></span>);
      <span class="pl-smi">recordBtn</span>.<span class="pl-smi">textContent</span> <span class="pl-k">=</span> <span class="pl-s"><span class="pl-pds">"</span>stop<span class="pl-pds">"</span></span>;
    }
    <span class="pl-en">console</span>.<span class="pl-c1">log</span>(<span class="pl-s"><span class="pl-pds">"</span>录音器状态：<span class="pl-pds">"</span></span>, <span class="pl-smi">mediaRecorder</span>.<span class="pl-smi">state</span>);
  };

  <span class="pl-smi">mediaRecorder</span>.<span class="pl-en">ondataavailable</span> <span class="pl-k">=</span> <span class="pl-smi">e</span> <span class="pl-k">=&gt;</span> {
    <span class="pl-smi">chunks</span>.<span class="pl-c1">push</span>(<span class="pl-smi">e</span>.<span class="pl-c1">data</span>);
  };

  <span class="pl-smi">mediaRecorder</span>.<span class="pl-en">onstop</span> <span class="pl-k">=</span> <span class="pl-smi">e</span> <span class="pl-k">=&gt;</span> {
    <span class="pl-k">var</span> blob <span class="pl-k">=</span> <span class="pl-k">new</span> <span class="pl-en">Blob</span>(chunks, { type<span class="pl-k">:</span> <span class="pl-s"><span class="pl-pds">"</span>audio/ogg; codecs=opus<span class="pl-pds">"</span></span> });
    chunks <span class="pl-k">=</span> [];
    <span class="pl-k">var</span> audioURL <span class="pl-k">=</span> <span class="pl-c1">window</span>.<span class="pl-c1">URL</span>.<span class="pl-en">createObjectURL</span>(blob);
    <span class="pl-smi">player</span>.<span class="pl-smi">src</span> <span class="pl-k">=</span> audioURL;
  };
},
() <span class="pl-k">=&gt;</span> {
  <span class="pl-en">console</span>.<span class="pl-c1">error</span>(<span class="pl-s"><span class="pl-pds">"</span>授权失败！<span class="pl-pds">"</span></span>);
}

);

} else {

console.error("浏览器不支持 getUserMedia");

}

运行

完成上面步骤后，实现了一个简单的录音功能，可通过此地址在线体验。完整的代码可在仓库 wayou/audio-recorder 中获取到。

刘哇勇的部落格