Encoding the stream myself using Base64Encode and flags set to 1 fixed my problem.

There is no CRLF anymore in my stream.

Here is my final solution (error handle ommited)

s stream=##class(%FileBinaryStream).%New()
s stream.Filename = filename
s encodedStream = ##class(%GlobalBinaryStream).%New()
while ('stream.AtEnd) {
      d encodedStream.Write(##class(%SYSTEM.Encryption).Base64Encode(stream.Read(12000),1))
}
s propertyPath = "PIDgrpgrp(1).ORCgrp(1).OBXgrp(1).OBX:5(1)"
s seg=target.GetMutableSegmentAt($P(propertyPath,":",1),.tSC)
s tSC = seg.StoreFieldStreamRaw(.encodedStream,$P(propertyPath,":",2))

Thanks Armin for your help.

Don't you think the problem might be StoreFieldStreamBase64 using Base64Encode from %SYSTEM.Encryption with default flags value at 0 ?

I'll try encoding the stream myself and using StoreFieldStreamRaw instead of  StoreFieldStreamBase64

If my solution doesn't work i'll try yours :)

Thanks

Second option : An OBX:5 with the value ABCDEFGHIJKL (get rid of all crlf)

[Updated last comment with code]

I need to add a file inside the obx:5(1) segment as a base64 encoded stream.

I'm using the StoreFieldStreamBase64 method from EnsLib.HL7.Segment.

This method add extra escaped CRLF inside my OBX segment and i don't know why.

When i write the hl7 message on disk with the new OBX segment, i can't parse it anymore with an EnsLib.HL7.Service.FileService, the extra crlf character is the problem.

Maybe i'm doing something wrong in my way to process the file.