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procedure Insert(const Stream, InsertStream: TStream; const Position: LongInt);
var
  MemoryStream: TMemoryStream;
begin
  if Position >= Stream.Size then begin
    Stream.Position := Stream.Size;
    Stream.CopyFrom(InsertStream, 0);
  end
  else begin
    Stream.Position := Position;
    MemoryStream := TMemoryStream.Create;
    try
      MemoryStream.CopyFrom(Stream, Stream.Size - Stream.Position);
      Stream.Position := Position;
      Stream.CopyFrom(InsertStream, 0);
      Stream.CopyFrom(MemoryStream, 0);
    finally
      MemoryStream.Free;
    end;
  end;
end;