Windows phone 8.1 播放音频文件的一部分

我必须播放一个大文件的音频部分（300MB+）

这是我的代码：

请注意有关流搜索和大小的评论。该文件从零位开始播放

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如何从指针到指针+长度播放声音？

我使用二进制读取器解决了我的问题。我读取字节缓冲区中所需的区域，并将其转换为irandomaccesstream

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此版本现在正在运行。

只是一个想法-也许您可以在加载后设置，并使用计时器（以适当的间隔）启动它，计时器将停止播放。音频部分是不同长度的语音。我无法估计讲话时间来设置计时器。

// Media source is a local file.
// datName = "sound.dat"
// pointer = position in file
// length  = length of the part to play

try
{
    file = await StorageFile.GetFileFromApplicationUriAsync
          (new Uri(@"ms-appx:///Data/" + datName));
    // Get the media source as a stream.
    IRandomAccessStream stream = 
          await file.OpenAsync(FileAccessMode.Read);
    stream.Seek((ulong)pointer); // This is working, position changes from 0 to pointer
    stream.Size = (ulong)length; // Is not working, Size remains unchanged at total file size
    media.SetSource(stream, file.ContentType);
    media.Play();
}
catch (Exception ex)
{
    if (ex is FormatException || ex is ArgumentException)
    {
        //ShowFileErrorMsg();
    }
}

StorageFile file = await StorageFile.GetFileFromApplicationUriAsync(new Uri(@"ms-appx:///Data/" + fileName));
using (Stream stream = (await file.OpenReadAsync()).AsStreamForRead())
using (BinaryReader reader = new BinaryReader(stream))
{
    reader.BaseStream.Position = pointer;
    byte[] buffer = reader.ReadBytes((int)length);
    IRandomAccessStream nstream = new MemoryStream(buffer).AsRandomAccessStream();
    media.SetSource(nstream, "");
    media.Play();
}