Play part of an audio file - windows-phone-8.1

Question

I have to play an audio part out of a big file (300MB+).
This is my code:
// 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();
}
}
Please note the comments on stream Seek and Size. The file is played from position zero.
How can I play the sound from pointer to pointer + length?

Answer 1

I've solved my problem by using the binary reader. I read the required area in a byte buffer and convert it to an IRandomAccessStream.
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();
}
This version is now working.