javascript - 实现拍照功能（详细示例代码）

介绍
HTML5 的 getUserMedia API 为用户提供访问硬件设备媒体（摄像头、视频、音频、地理位置等）的接口，基于该接口，开发者可以在不依赖任何浏览器插件的条件下访问硬件媒体设备。

另外，主流浏览器 Firefox、Chrome、Safari、Opera 等等已经全面支持。

一、获取视频流，并用 video 标签播放

 <video id="video" autoplay></video>

const videoConstraints = { width: 1366, height: 768 };
const videoNode = document.querySelector('#video');
let stream = await navigator.mediaDevices.getUserMedia({ audio: true, video: videoConstraints });
videoNode.srcObject = stream;
videoNode.play();

二、多个摄像头设备切换

// enumerateDevices获取所有媒体设备
const mediaDevices = await navigator.mediaDevices.enumerateDevices();

// 通过设备实例king属性videoinput，过滤获取摄像头设备
const videoDevices = mediaDevices.filter(item => item.kind === 'videoinput') || [];

// 获取前置摄像头
const videoDeviceId = videoDevices[0].deviceId;
const videoConstraints = { deviceId: { exact: videoDeviceId }, width: 1366, height: 768 };
let stream = await navigator.mediaDevices.getUserMedia({ audio: true, video: videoConstraints });

// 获取后置摄像头
const videoDeviceId = videoDevices[1].deviceId;
const videoConstraints = { deviceId: { exact: videoDeviceId }, width: 1366, height: 768 };
let stream = await navigator.mediaDevices.getUserMedia({ audio: true, video: videoConstraints });

// 依次类推...

三、拍照保存图片

// 通过canvas捕捉video流，生成base64格式图片
const canvas = document.createElement('canvas');
const context = canvas.getContext('2d');
canvas.width = 1366;
canvas.height = 768;
context.drawImage(videoNode, 0, 0, canvas.width, canvas.height);
download(canvas.toDataURL('image/jpeg'));

// 下载图片
function download (src) {
? ?if (!src) return;
? ?const a = document.createElement('a');
? ?a.setAttribute('download', new Date());
? ?a.href = src;
? ?a.click();
}

关闭摄像头设备
?

let stream = await navigator.mediaDevices.getUserMedia({ audio: true, video: videoConstraints });
// 3s后关闭摄像头
setTimeout(function () {
? ? stream.getTracks().forEach(track => track.stop());
? ? stream = null;
}, 3000);