1.elementUI  el-upload组件上传，on-change 触发校验

<el-upload size="small" v-if="!fileList.length"
    class="upload-demo"
    :action="uploadUrl"
    :headers="headers"
    :on-change="onChange"
    :on-success="onSuccess"
    :on-exceed ="onExceed"
    :on-remove="handleRemove"
    :before-upload="beforeUpload"
    :multiple = 'false'
    accept=".mp4,.MP4"
    :limit="1"
    list-type="picture-card"
    :file-list="fileList">
    <div class="upload-img-modify"></div>
    <div slot="tip" class="el-upload__tip">请上传mp4格式的视频文件</div>
</el-upload>

2. audio获取录音时长，也可获取视频的时长

 // 文件上传onchange事件
onChange(file, fileList){
    let that = this;
    let imgSize = Number(file.size / 1024 / 1024);
    if (imgSize > 100) {
        this.$message.info('视频大小不能大于100M');
        this.fileList = [];
        return;
    } 
    var url = URL.createObjectURL(file.raw);//获取录音时长
    var audioElement = new Audio(url);//audio也可获取视频的时长
    var duration;
    audioElement.addEventListener("loadedmetadata", function (_event) {
        duration = audioElement.duration;
        that.formAdd.videoTime = parseInt(duration);
    });
    this.fileList = fileList;
},