html有本地上传替换部分，可以不看

原理：通过video标签对视频进行加载，随后使用canvas对截取的视频帧生成需要的图片

<template>
<el-row  :gutter="18"  class="preview-video"><h4>视频预览<span>系统默认选中第一帧为封面</span></h4><div class="screenshot-box"><video:class="`screenshot-video screenshot-video${id}`":src="videoUrl"controlscrossorigin="anonymous"/></div><div class="preview-btn"><el-button size="small" type="primary" class="set-btn" @click="setWidthHeight">截取封面</el-button><el-uploadaction="":key="componentImgKey":on-change="handleAddLocalImage"accept=".jpg,.png,.jpeg,.JPG,.PNG,.JPEG":auto-upload="false":show-file-list="false":limit="1":multiple="false"ref="uploads"><el-button @click.native="handleAddLocalImageBefore" size="small" type="primary">本地上传</el-button></el-upload></div><canvas:class="`myCanvas${id}`"class="myCanvas":width="isWidth":height="isHeight"/></el-row></template>
<script>
export default {data(){return {videoUrl:"",id: 0,isWidth: 320,isHeight: 180,imgSrc:"",},methods:{setWidthHeight() {if (true) {this.$nextTick((_) => {var v = document.querySelector(`.screenshot-video${this.id}`);this.isWidth = v.offsetWidth;this.isHeight = v.offsetHeight;this.cutPicture();});}},//截取当前帧的图片cutPicture() {if (process.browser) {this.$nextTick((_) => {var v = document.querySelector(`.screenshot-video${this.id}`);let canvas = document.querySelector(`.myCanvas${this.id}`);var ctx = canvas.getContext("2d");ctx.drawImage(v, 0, 0, this.isWidth, this.isHeight);var oGrayImg = canvas.toDataURL("image/png");this.imgSrc = oGrayImg;this.file_ext="png"let size=this.imageSize(oGrayImg)/1024/1024if(size>2){this.$message.error("图片大小不能超过2MB！")return}});}},imageSize(base64Str) {const indexBase64 = base64Str.indexOf('base64,');if (indexBase64 < 0) return -1;const str = base64Str.substr(indexBase64 + 6);return (str.length * 0.75).toFixed(2);},}
}
</script>