无法使用读/写流正确解析和重组二进制文件

I'm trying to get certain segments of a binary file and then recombine them into a condensed format. However, upon completion of this task the binary data is scrambled in a semi-random order. In fact, the first roughly 15k bytes are correct then conflicts occur continuously after this. What is going wrong? I believe that these streams are running into one another (for lack of a better metaphor) and the resultant byte length is correct. Why is this happening? I thought I was taking adequate precautions as to asynchronicity?I'm trying to get certain segments of a binary