title: Is the leading structure in MP3 file a real frame?
body: <p>I'm now doing some work with decoding MP3 files, but just have some basic knowledge about the MP3 file. I implement a simple decoder for MP3 these days. When comparing the decoded result with that of <a href="http://maaate.sourceforge.net/" rel="noreferrer">Maaate</a> decoder, I encounter this problem.</p>
  
  <p>My decoder extract one more frame than the Maaate decoder. After scrutinizing the result of a sample MP3 file, I find the first frame is abnormal. For my sample file, the first frame is 413 bytes long with frame header <code>0xfffb9064</code> different from all the other frames with 100 byte-length and header <code>0xfffb1064</code>.</p>
  
  <p><strong>My question is</strong>:
  Is the first "frame" in the result a real frame? Is so, why it seems different from others? If not, what is this structure used for and how to distinguish it from others for both of them share the frame sync code <code>0xfff</code>?</p>