There was a question on 05 Jun 2007 about the IsValidFormat method call which
uses the FileStream as an input.

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   Does anyone knows exactly what happnes to the stream when
RawDecoder->IsValidFormat(Stream) is called?  Sometimes when I
called IsValidFormat method for the first time to a stream, it
will return false, then if I immediately call the method again
using the same stream, then it will return true.  What's the reason
that the second call to the same stream returns a different result?
 Does the method move the stream reading position?  The RAW image I
used is from one of the cameras that listed as supported cameras
in the DotImage's documentation.

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The answer was....

This is most likely because the stream is not at the beginning the
first time you call IsValidFormat.  I believe the IsValidFormat
method will seek to the beginning after it's performed its check
on the data, which is why the second time it works.

Just call the stream.Seek method to move it to the beginning of the
stream before calling IsValidFormat.

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I was able to do this for IsValidFormat but I am having trouble
with the Read method. I have a file which contains a header and then
the codestream data. I am trying to set the file stream pointer to the
beginning of the codestream and then read. I did this and it worked for IsValidFormat.
When I set the filestream pointer to the beginning of the data in
the codestream and then call a Read, I get a Jp2StartDecompress
exception.