WebRTC网页打开摄像头并录制视频

落寞的鱼丶

发布于 2022-02-26 12:07:54

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代码可运行

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代码可运行

前面我们能打开本地摄像头，并且在网页上看到摄像头的预览图像。本文我们使用MediaRecorder来录制视频。在网页上播放录制好的视频，并能提供下载功能。

html#

首先创建一个html界面，放上一些元素

    <video id="v1" playsinline autoplay muted></video>
    <video id="v2" playsinline loop></video>

    <div>
        <button id="startCamera">开启摄像头</button>
        <button id="stopCamera">停止摄像头</button>
        <button id="record" disabled>录制</button>
        <button id="play" disabled>播放</button>
        <button id="download" disabled>下载视频</button>
    </div>
    <div> 录制使用的视频格式: <select id="codecSelect" disabled></select> </div>
    <div>
        <h4>视频设置</h4>
        <p>回声消除: <input type="checkbox" id="echoCancellation"></p>
    </div>
    <div> <span id="msg" style="font-size:smaller"></span> </div>

    <!-- 使用本地的适配器 -->
    <script src="../js/adapter-latest.js" async></script>

video
- v1 用来预览
- v2 用来播放录制好的视频
button 控制摄像头开启、录制，下载等等
select 选择录制用的视频格式
input 选择回声消除

js#

准备#

先把界面上的元素拿到

'use strict';

let mediaRecorder;
let recordedBlobs; // 录制下来的内容
let isRecording = false;

// 先把页面元素拿到
const startCameraBtn = document.querySelector('button#startCamera'); // 启动摄像头按钮
const stopCameraBtn = document.querySelector('button#stopCamera');
const recordBtn = document.querySelector('button#record'); // 开始录制按钮
const playBtn = document.querySelector('button#play');     // 播放按钮
const downloadBtn = document.querySelector('button#download'); // 下载视频按钮
const codecSelector = document.querySelector('#codecSelect'); // 选择格式
const msgEle = document.querySelector('span#msg');         // 显示消息
const previewV1 = document.querySelector('video#v1'); // 预览用的
const recordedV2 = document.querySelector('video#v2');  // 用来播放录制好的视频

视频支持的格式#

先预定几个可能的格式，然后一个个来判断是否支持。找到支持的格式。

function getSupportedMimeTypes() {
  const possibleTypes = [
    'video/webm;codecs=vp9,opus',
    'video/webm;codecs=vp8,opus',
    'video/webm;codecs=h264,opus',
    'video/mp4;codecs=h264,aac',
  ];
  return possibleTypes.filter(mimeType => {
    return MediaRecorder.isTypeSupported(mimeType);
  });
}

开启摄像头#

同样要使用getUserMedia方法。这里给视频指定了宽高。回声消除是可选项。

// 启动摄像头
startCameraBtn.addEventListener('click', async () => {
  startCameraBtn.disabled = true;
  const isEchoCancellation = document.querySelector('#echoCancellation').checked;
  const constraints = {
    audio: {
      echoCancellation: { exact: isEchoCancellation }
    },
    video: {
      width: 1280, height: 720
    }
  };
  await init(constraints);
});

async function init(constraints) {
  try {
    const stream = await navigator.mediaDevices.getUserMedia(constraints);
    gotStream(stream);
  } catch (e) {
    showMsg(`navigator.getUserMedia error:${e.toString()}`);
  }
}

function gotStream(stream) {
  recordBtn.disabled = false;
  showMsg('拿到了 stream:', stream);
  window.stream = stream;
  previewV1.srcObject = stream;

  // 重置
  var codecOption = codecSelector.lastChild;
  while (codecOption != null) {
    codecSelector.removeChild(codecOption);
    codecOption = codecSelector.lastChild;
  }

  getSupportedMimeTypes().forEach(mimeType => {
    const option = document.createElement('option');
    option.value = mimeType;
    option.innerText = option.value;
    codecSelector.appendChild(option);
  });
  codecSelector.disabled = false; // 可以进行选择了
}

下面是停止摄像头的方法

stopCameraBtn.addEventListener('click', () => {
  var stream = previewV1.srcObject;
  if (stream == null) {
    return;
  }
  const tracks = stream.getTracks();
  tracks.forEach(function (track) {
    track.stop();
  });
  previewV1.srcObject = null;
  window.stream = null;
  codecSelector.disabled = true;
  startCameraBtn.disabled = false;
});

开始录制#

开始录制视频

function startRecording() {
  recordedBlobs = [];
  const mimeType = codecSelector.options[codecSelector.selectedIndex].value;
  const options = { mimeType };

  try {
    mediaRecorder = new MediaRecorder(window.stream, options);
  } catch (e) {
    showMsg(`创建MediaRecorder出错: ${JSON.stringify(e)}`);
    return;
  }

  showMsg('创建MediaRecorder', mediaRecorder, ' -> options', options);
  recordBtn.textContent = '停止录制';
  isRecording = true;
  playBtn.disabled = true;
  downloadBtn.disabled = true;
  codecSelector.disabled = true;
  mediaRecorder.onstop = (event) => {
    showMsg('录制停止了: ' + event);
    showMsg('录制的数据Blobs: ' + recordedBlobs);
  };
  mediaRecorder.ondataavailable = handleDataAvailable;
  mediaRecorder.start();
  showMsg('录制开始 mediaRecorder: ' + mediaRecorder);
}

function handleDataAvailable(event) {
  if (event.data && event.data.size > 0) {
    recordedBlobs.push(event.data);
  }
}

recordBtn.addEventListener('click', () => {
  if (isRecording == false) {
    startRecording();
  } else {
    stopRecording();
    recordBtn.textContent = '开始录制';
    playBtn.disabled = false;
    downloadBtn.disabled = false;
    codecSelector.disabled = false;
  }
});

重置录制内容recordedBlobs = []
拿到选定的视频格式mimeType
新建MediaRecorder对象，传入前面获取到的流
处理各个按钮（ui）的状态
mediaRecorder
- 设置停止监听器 onstop
- 监听录制数据 ondataavailable，有数据来的时候存放在recordedBlobs
- 启动录制 mediaRecorder.start()

停止录制#

function stopRecording() {
  mediaRecorder.stop();
}

播放录制好的视频#

录制好的视频内容存放在recordedBlobs。新建Blob，交给video（recordedV2）来播放

playBtn.addEventListener('click', () => {
  const mimeType = codecSelector.options[codecSelector.selectedIndex].value.split(';', 1)[0];
  const superBuffer = new Blob(recordedBlobs, { type: mimeType });
  recordedV2.src = null;
  recordedV2.srcObject = null;
  recordedV2.src = window.URL.createObjectURL(superBuffer);
  recordedV2.controls = true;
  recordedV2.play();
});

下载视频#

录制好的视频内容存放在recordedBlobs。

downloadBtn.addEventListener('click', () => {
  const blob = new Blob(recordedBlobs, { type: 'video/webm' });
  const url = window.URL.createObjectURL(blob);
  const a = document.createElement('a');
  a.style.display = 'none';
  a.href = url;
  a.download = '视频_' + new Date().getTime() + '.webm';
  document.body.appendChild(a);
  a.click();
  setTimeout(() => {
    document.body.removeChild(a);
    window.URL.revokeObjectURL(url);
  }, 100);
});