vant上传视频获取时长并限制（苹果安卓共用）

   beforeRead(file) {
      var url = URL.createObjectURL(file)
      var audioElement = new Audio(url)
      var result
      audioElement.muted = true
      audioElement.play().then(() => audioElement.pause())
      return new Promise((resolve, reject) => {
        audioElement.addEventListener('loadedmetadata', function() {
          // 视频时长值的获取要等到这个匿名函数执行完毕才产生
          result = audioElement.duration //得到时长为秒，小数，182.36
          var serce = parseInt(result)
          if (serce > 120) {
            audioElement.muted = false
            Toast('视频不能超过2分钟')
            reject()
          } else {
            audioElement.muted = false
            resolve()
          }
        })
      })
    },