Cordova 文件插件 readAsDataURL 不返回文件数据

我尝试使用 Cordova 文件插件的 readAsDataURL 函数来获取视频文件的 base64 版本，但没有成功。我的代码如下所示：

  recordVideo()
  {
    return new Promise(resolve =>
    {
      let options: CaptureVideoOptions = { limit: 1, duration: 2 };
      MediaCapture.captureVideo(options)
        .then(
          (data: MediaFile[]) => {

            console.log('Media: recordVideo: cordova.file.dataDirectory = ' + cordova.file.dataDirectory + ', path = ' + data[0].fullPath.substring(1));

            // Turn the video file into base64
            let base64File = File.readAsDataURL(cordova.file.dataDirectory, data[0].fullPath.substring(1));

            console.log('Media: recordVideo: got video with data = ' + JSON.stringify(data));

            console.log('Media: recordVideo: base64File = ' + JSON.stringify(base64File));

            resolve(data);
          },
          (err: CaptureError) => console.error('ERROR - Media: recordVideo: captureVideo error = ' + err)
        );
    });
  }

第一个的输出console.log显示传递给的参数值readAsDataURL:

Media: recordVideo: cordova.file.dataDirectory = file:///var/mobile/Containers/Data/Application/764345DC-A77D-43C2-9DF7-CDBE6A0DC372/Library/NoCloud/, path = private/var/mobile/Containers/Data/Application/764345DC-A77D-43C2-9DF7-CDBE6A0DC372/tmp/50713961066__4FD8AF8D-BD36-43A4-99CC-F328ADFD7E38.MOV

第二console.log显示 MediaCapture 插件返回的数据：

Media: recordVideo: got video with data = [{"name":"50713961066__4FD8AF8D-BD36-43A4-99CC-F328ADFD7E38.MOV","localURL":"cdvfile://localhost/temporary/50713961066__4FD8AF8D-BD36-43A4-99CC-F328ADFD7E38.MOV","type":"video/quicktime","lastModified":null,"lastModifiedDate":1485446813000,"size":195589,"start":0,"end":0,"fullPath":"/private/var/mobile/Containers/Data/Application/764345DC-A77D-43C2-9DF7-CDBE6A0DC372/tmp/50713961066__4FD8AF8D-BD36-43A4-99CC-F328ADFD7E38.MOV"}]

最后console.log显示返回的值readAsDataURL:

Media: recordVideo: base64File = {"__zone_symbol__state":null,"__zone_symbol__value":[]}

几乎没有关于使用它的文档（我可以找到）。

函数 readAsDataURL 获取路径和文件名作为参数并返回一个承诺。用法是

File.readAsDataURL("path_to_the_FileName", "Filename").then(result => {
  this.base64File = result;
});

根据控制台日志，文件名和文件名的完整路径是从数据中获取的（从 MediaCapture.captureVideo 返回的承诺）。

所以你可以像下面这样使用它

var path = "file://"+data[0].fullPath.substring(7,data[0].fullPath.lastIndexOf("/"))‌​; 
File.readAsDataURL(path, data[0].name).then(result => { 
  this.base64File = result;
}