起因

当前程序是以electron + vue作为前端，go作为后端http主服务。最近新来了一个需求，需要能够使用多个PC USB摄像头进行录像，并能够区分到底是哪个摄像头在录，这就需要前端页面能够实时的展示摄像头视频。

实现方式

  1. 浏览器支持(例：chrome)，直接调用js的MediaRecorder对象来处理。
  2. 搭建rtmp服务器，通过推流（如：ffmpeg）和拉视频流的方式展示视频。
  3. 后端通过ffmpeg获取视频流，转成图片发给界面展示。

浏览器的MediaRecorder

fileSaver.js 用于浏览器保存文件

<!DOCTYPE html>
<html>

<head>
	<title>video recoder</title>
	<script src="./fileSaver.js"></script>
	<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
	<meta charset="utf-8">
	<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=no">
	<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
	<!-- <meta http-equiv="Content-Security-Policy" content="upgrade-insecure-requests"> -->
</head>
<style>
	body {
		background-color: #EFEDEF;
	}
</style>

<body>
	<article style="border:1px solid white;width:400px;height:400px;margin:0 auto;background-color:white;">

		<section class="experiment" style="width:320px; height:240px;border:1px solid green; margin:50px auto;">
			<div id="videos-container" style="width:320px; height:240px;">
			</div>
		</section>
		<section class="experiment" style="text-align:center;border:none; margin-top:20px;">
			<button id="openCamera">打开摄像头</button>
			<button id="start-recording" disabled>开始录制</button>
			<button id="save-recording" disabled>保存</button>
			<!--<a href="javascript:void(0)" οnclick="send()">发送</a>-->
		</section>
	</article>
	<!-- <div style="display:none;"> -->
	<!-- <div>
		<button οnclick="tGet();">测试https请求</button>
	</div> -->
	<script>
		var mediaStream;
		var recorderFile;
		var stopRecordCallback;
		var openBtn = document.getElementById("openCamera");
		var startBtn = document.getElementById("start-recording");
		var saveBtn = document.getElementById("save-recording");
		openBtn.onclick = function () {
			this.disabled = true;
			startBtn.disabled = false;
			openCamera();
		};

		startBtn.onclick = function () {
			this.disabled = true;
			startRecord();
		};

		saveBtn.onclick = function () {
			saver();

			// alert('Drop WebM file on Chrome or Firefox. Both can play entire file. VLC player or other players may not work.');
		};

		var mediaRecorder;
		var videosContainer = document.getElementById('videos-container');

		function openCamera() {
			var len = videosContainer.childNodes.length;
			for (var i = 0; i < len; i++) {
				videosContainer.removeChild(videosContainer.childNodes[i]);
			}

			var video = document.createElement('video');

			var videoWidth = 320;
			var videoHeight = 240;

			video.controls = false;
			video.muted = true;
			video.width = videoWidth;
			video.height = videoHeight;
			MediaUtils.getUserMedia(true, false, function (err, stream) {
				if (err) {
					throw err;
				} else {
					// 通过 MediaRecorder 记录获取到的媒体流
					console.log("通过 MediaRecorder 记录获取到的媒体流");
					mediaRecorder = new MediaRecorder(stream);
					mediaStream = stream;

					var chunks = [],
						startTime = 0;
					video.srcObject = stream;
					video.play();

					videosContainer.appendChild(video);
					mediaRecorder.ondataavailable = function (e) {
						console.log("ondataavailable:", e)
						mediaRecorder.blobs.push(e.data);
						chunks.push(e.data);

						// f = new Blob([e.data], {
						// 	'type': mediaRecorder.mimeType
						// });
						// send1(f);
					};
					mediaRecorder.blobs = [];

					mediaRecorder.onstop = function (e) {
						recorderFile = new Blob(chunks, {
							'type': mediaRecorder.mimeType
						});
						chunks = [];
						if (null != stopRecordCallback) {
							stopRecordCallback();
						}
					};
				}
			});
		}

		// 停止录制
		function stopRecord(callback) {
			stopRecordCallback = callback;
			// 终止录制器
			mediaRecorder.stop();
			// 关闭媒体流
			MediaUtils.closeStream(mediaStream);
		}

		var MediaUtils = {
			/**
			 * 获取用户媒体设备(处理兼容的问题)
			 * @param videoEnable {boolean} - 是否启用摄像头
			 * @param audioEnable {boolean} - 是否启用麦克风
			 * @param callback {Function} - 处理回调
			 */
			getUserMedia: function (videoEnable, audioEnable, callback) {
				navigator.getUserMedia = navigator.getUserMedia || navigator.webkitGetUserMedia || navigator
					.mozGetUserMedia ||
					navigator.msGetUserMedia || window.getUserMedia;
				var constraints = {
					video: videoEnable,
					audio: audioEnable
				};
				if (navigator.mediaDevices && navigator.mediaDevices.getUserMedia) {
					navigator.mediaDevices.getUserMedia(constraints).then(function (stream) {
						callback(false, stream);
					})['catch'](function (err) {
						callback(err);
					});
				} else if (navigator.getUserMedia) {
					navigator.getUserMedia(constraints, function (stream) {
						callback(false, stream);
					}, function (err) {
						callback(err);
					});
				} else {
					callback(new Error('Not support userMedia'));
				}
			},

			/**
			 * 关闭媒体流
			 * @param stream {MediaStream} - 需要关闭的流
			 */
			closeStream: function (stream) {
				if (typeof stream.stop === 'function') {
					stream.stop();
				} else {
					let trackList = [stream.getAudioTracks(), stream.getVideoTracks()];

					for (let i = 0; i < trackList.length; i++) {
						let tracks = trackList[i];
						if (tracks && tracks.length > 0) {
							for (let j = 0; j < tracks.length; j++) {
								let track = tracks[j];
								if (typeof track.stop === 'function') {
									track.stop();
								}
							}
						}
					}
				}
			}
		};

		function startRecord() {
			mediaRecorder.start();
			// mediaRecorder.start(5000);
			setTimeout(function () {
				// 结束
				stopRecord(function () {
					console.log("录制成功!");
					openBtn.disabled = false;
					saveBtn.disabled = false;
					console.log(recorderFile);
					// 直接保存
					// saver();
					// alert("保存成功");
					// send();
				});
			}, 1000 * 5);
		}

		function saver() {
			var file = new File([recorderFile], 'msr-' + (new Date).toISOString().replace(/:|\./g, '-') + '.mp4', {
				type: 'video/mp4'
			});
			saveAs(file);
		}

		function send() {
			var file = new File([recorderFile], 'msr-' + (new Date).toISOString().replace(/:|\./g, '-') + '.mp4', {
				type: 'video/mp4'
			});
			var data = new FormData();
			data.append("username", "test");
			data.append("file", file);

			var req = new XMLHttpRequest();
			req.open("POST", "http://127.0.0.1:4780/upload");
			req.send(data);
		}

		function send1(bbb) {
			var file = new File([bbb], 'msr-' + (new Date).toISOString().replace(/:|\./g, '-') + '.webm', {
				type: 'video/webm'
			});
			var data = new FormData();
			data.append("username", "test");
			data.append("file", file);

			var req = new XMLHttpRequest();
			// req.open("POST", "http://127.0.0.1:4780/upload");
			req.open("POST", "https://127.0.0.1:7080/upload");
			req.send(data);
		}

		function tGet() {
			timedGetTest("https://127.0.0.1:7080", 5000)
		}

		function timedGetTest(url, time, callback) {
			var request = new XMLHttpRequest();
			var timeout = false;
			var timer = setTimeout(function () {
				console.log("超时了：", arguments);
				timeout = true;
				request.abort();
			}, time);
			request.open("GET", url);
			request.onreadystatechange = function () {
				console.log(arguments);
				if (request.readyState !== 4) return;
				if (timeout) return;
				clearTimeout(timer);
				if (request.status === 200) {
					callback(request.responseText);
				}
			}
			request.send(null);
		}
	</script>

</body>

</html>

直播推流拉流式

主要使用了开源库livego来作为rtmp服务器（其支持的协议有RTMP/AMF/HLS/HTTP-FLV），具体的详细介绍与使用，可以上github自行查看。

ffmpeg直接获取视频流，转换为图片发送给前端进行展示

用go语言实现，主要的难点就是cgo，需要通过cgo集成C的相关代码，获取视频流，然后转成图片即可。或者使用别人已经集成好的开源库goav进行相应的操作。

总结

本篇主要是讲了下web展示摄像头内容的几种实现方式，做个记录，也了解了一下直播相关的一些知识。通过开源库livego和flv.js搭建了一下直播客户端和服务器，使用OBS Studio进行视频推流，自己随便玩了一下，感兴趣的也可以自己尝试着搭建玩玩。

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