title: Determine that a particular file is in fact a 3gp file
body: <p>I do scanning of file system and I need identify all 3gp files. </p>
  
  <p>Usually, for noting that particular file is of certain format, developers of that format make  marks.</p>
  
  <p>E.g.  first bytes of  FLV are 46 4C 56 01, if it's so, one can be sure that this is FLV format (if no one changed it intentionally, of course), etc.</p>
  
  <p>I'd be glad to identify 3gp files in the same way, but which bytes do indicate that?</p>