https://developers.weixin.qq.com/miniprogram/dev/api/media/video/wx.chooseMedia.html

示例代码的 `res.tempFiles` 是个数组，不是对象，直接访问 `res.tempFiles.tempFilePath` 返回的是 undefined

wx.chooseMedia({
  count: 9,
  mediaType: ['image','video'],
  sourceType: ['album', 'camera'],
  maxDuration: 30,
  camera: 'back',
  success(res) {
    console.log(res.tempFiles.tempFilePath)
    console.log(res.tempFiles.size)
  }
})