复现代码如下：
wx.chooseMedia({
      mediaType:['video'],
      sourceType:['camera'],
      camera:'back',
      // maxDuration:30,
      success(res){
        console.log('video res',res)
        console.log('FilePath==========>',res.tempFiles[0].thumbTempFilePath)
        that.setData({
          video:res.tempFiles[0].tempFilePath
        })
      },
      fail(res){
        console.log('failed res:',res)
      }
    })