js获取视频时长

//获取视频时长
       if (names.indexOf('mp4') > -1) {
         const reader = new FileReader()
         const rs = reader.readAsArrayBuffer(file.file)
         let blob = null
         reader.onload = (e) => {
           if (typeof e.target.result === 'object') {
             blob = new Blob([e.target.result])
           } else {
             blob = e.target.result
           }
           if (blob == null) return
           const url = URL.createObjectURL(blob)
           const audioElement = new Audio(url)
           let duration
           const fun = (duration) => {
             this.duration = duration
             console.log('视频时长：', this.duration)
           }
           //下面需要注意的是在监听loadedmetadata绑定的事件中对duration直接进行赋值是无效的，需要在fun回调函数中进行赋值
           audioElement.addEventListener('loadedmetadata', function () {
             //音频/视频的元数据已加载时，会发生 loadedmetadata 事件
             duration = audioElement.duration //时长以秒作为单位
             fun(parseFloat(duration).toFixed(1))
           })
         }
       }