有个问题实在太莫名其妙，怎么也想不通怎么回事。我按照这个文档：https://msdn.microsoft.com/zh-cn/windows/uwp/audio-video-camera/media-playback-with-mediasource 说的那样，编写下面的代码：
private async void btnOpen_Click(object sender, RoutedEventArgs e)
{
//Create a new picker
var filePicker = new FileOpenPicker();
//Add filetype filters. In this case wmv and mp4.
filePicker.FileTypeFilter.Add(".wmv");
filePicker.FileTypeFilter.Add(".mp4");
filePicker.FileTypeFilter.Add(".mkv");
//Set picker start location to the video library
filePicker.SuggestedStartLocation = PickerLocationId.VideosLibrary;
//Retrieve file from picker
StorageFile file = await filePicker.PickSingleFileAsync();
if (file != null)
{
MediaSource mediaSource = MediaSource.CreateFromStorageFile(file);
MediaPlaybackItem mediaPlaybackItem = new MediaPlaybackItem(mediaSource);
}
}
我的目的是要通过MediaPlaybackItem的AudioTracks属性获取一些我必要的信息，但莫名其妙的是，通过断点调试，无论我打开什么视频文件，mediaSource的Duration属性总是null，而mediaPlaybackItem的AudioTracks属性里的SelectedIndex却总是-1，完全无法像各种官方文档说的那样得到我想得到的信息，究竟搞什么鬼？
