我在页面上有一个Button,按钮的click事件使用以下方法:
StorageFile _sourceFile;
private string _sourceToken;
private async void btnSelect_Click(object sender, RoutedEventArgs e)
{
FileOpenPicker fop = new FileOpenPicker();
fop.FileTypeFilter.Add(".mp4");
StorageFile inFile = await fop.PickSingleFileAsync();
_sourceToken = Windows.Storage.AccessCache.StorageApplicationPermissions.FutureAccessList.Add(inFile);
_sourceFile = await Windows.Storage.AccessCache.StorageApplicationPermissions.FutureAccessList.GetFileAsync(_sourceToken);
mediaElement.AutoPlay = false;
IRandomAccessStream stream = await _outFile.OpenAsync(FileAccessMode.ReadWrite);
mediaElement.SetSource(stream, _outFile.ContentType);
}
如果我点击MediaElement上的播放,我选择的视频就可以正常播放。
我还有另一个按钮,其点击事件中包含以下代码:
private async void btnExport_Click(object sender, RoutedEventArgs e)
{
StorageFile outFile = await KnownFolders.VideosLibrary.CreateFileAsync("Outfie.mp4", CreationCollisionOption.ReplaceExisting);
MediaEncodingProfile profile = MediaEncodingProfile.CreateMp4(VideoEncodingQuality.HD1080p);
MediaTranscoder transcoder = new MediaTranscoder();
PrepareTranscodeResult prepareOp = await transcoder.PrepareFileTranscodeAsync(_sourceFile, outFile, profile);
if (prepareOp.CanTranscode)
{
var transcodeOp = prepareOp.TranscodeAsync();
transcodeOp.Progress += new AsyncActionProgressHandler<double>(TranscodeProgress);
transcodeOp.Completed += new AsyncActionWithProgressCompletedHandler<double>(TranscodeComplete);
}
else
{
switch (prepareOp.FailureReason)
{
case TranscodeFailureReason.CodecNotFound:
System.Diagnostics.Debug.WriteLine("Codec not found.");
break;
case TranscodeFailureReason.InvalidProfile:
System.Diagnostics.Debug.WriteLine("Invalid profile.");
break;
default:
System.Diagnostics.Debug.WriteLine("Unknown failure.");
break;
}
}
}
不幸的是,行transcoder.PrepareFileTranscodeAsync抛出了UnauthorizedAccessException。但是如果我使用以下代替_sourceFile它可以工作:
StorageFile sourceFile = await KnownFolders.VideosLibrary.GetFileAsync("sourceFile.mp4");
抛出的错误是:
System.UnauthorizedAccessException:&#39;访问被拒绝。 (HRESULT异常:0x80070005(E_ACCESSDENIED))&#39;
要清楚,我选择了KnownFolders Enumeration外的文件,因此我使用的是Windows.Storage.AccessCache.StorageApplicationPermissions.FutureAccessList。
任何人都可以解释原因吗?
编辑: 如果我将源文件更改为FileOpenPicker的结果,那么它可以工作。所以它引出了一个问题,为什么FutureAccessList不工作?
private async void btnExport_Click(object sender, RoutedEventArgs e)
{
StorageFile outFile = await KnownFolders.VideosLibrary.CreateFileAsync("Outfie.mp4", CreationCollisionOption.ReplaceExisting);
FileOpenPicker fop = new FileOpenPicker();
fop.SuggestedStartLocation = PickerLocationId.ComputerFolder;
fop.FileTypeFilter.Add(".mp4");
StorageFile sourceFile = await fop.PickSingleFileAsync();
MediaEncodingProfile profile = MediaEncodingProfile.CreateMp4(VideoEncodingQuality.HD1080p);
MediaTranscoder transcoder = new MediaTranscoder();
PrepareTranscodeResult prepareOp = await transcoder.PrepareFileTranscodeAsync(sourceFile, outFile, profile);
if (prepareOp.CanTranscode)
{
var transcodeOp = prepareOp.TranscodeAsync();
transcodeOp.Progress += new AsyncActionProgressHandler<double>(TranscodeProgress);
transcodeOp.Completed += new AsyncActionWithProgressCompletedHandler<double>(TranscodeComplete);
}
else
{
switch (prepareOp.FailureReason)
{
case TranscodeFailureReason.CodecNotFound:
System.Diagnostics.Debug.WriteLine("Codec not found.");
break;
case TranscodeFailureReason.InvalidProfile:
System.Diagnostics.Debug.WriteLine("Invalid profile.");
break;
default:
System.Diagnostics.Debug.WriteLine("Unknown failure.");
break;
}
}
}
答案 0 :(得分:1)
您是否可以访问您尝试写入的文件?也许它是只读的或由您自己以外的其他用户创建的? (在资源管理器中右键单击+属性可以让您更清楚地了解文件权限)
此外,如果您尝试写入您无法访问的文件夹,则可能会遇到该例外情况。
检查您的凭据,我猜它的相关内容。
答案 1 :(得分:1)
所以我似乎是在ReadWrite模式下打开源文件
IRandomAccessStream stream = await _outFile.OpenAsync(FileAccessMode.ReadWrite);
是问题的原因。根据{{3}}页面
只有当您准备好立即按 编写时才使用读/写模式,以避免与其他操作发生冲突。
所以我改为这个并且一切正常
IRandomAccessStream stream = await _outFile.OpenAsync(FileAccessMode.Read);