Avi File empty property Sheet (Closing Files in C#)

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C#

Windows

Win8

I wrote a class to write an avi file byte per byte. It works fine, Media Player and Virtual Dub can play and handle the video. The problem is, the video details in the Windows property sheet are completely empty, no heigth, width, etc.. I compare the header to a fully functional file in a hexeditor. There are no layout differences.
Any guess what is wrong?
Or do someone know how the Windows property Sheet works?

NEW AWARENESS
I repaired the file with VirtualDub and everything works fine. Then i built the same bytes in my code and i did not work anymore (Video plays, but no properties in Windows explorer):
My conclusion is, it has to do with closing the file or something like this!

Here is my code for open and close the file:

FileInfo fi = new FileInfo("test.avi");
FileStream aviFile = fi.Create();
BinaryWriter writer = new BinaryWriter(aviFile);
//writer.Write(Encoding.UTF8.GetBytes("example"));
//writer writes a lot of bytes
writer.Close();
aviFile.Close();

Is there another possibility to write in a file? Or do i miss something?

Thanks