code: @SuppressWarnings("unused")
      private boolean checkSwf() throws IOException {
  		//get rid of the last byte of the signature, the byte of the version and 4 bytes of the size
  		byte[] a = new byte[6];
  		if (read(a) != a.length) {
  			return false;
  		}
  		format = FORMAT_SWF;
  		int bitSize = (int)readUBits( 5 );
  		int minX = (int)readSBits( bitSize ); // unused, but necessary
  		int maxX = (int)readSBits( bitSize );
  		int minY = (int)readSBits( bitSize ); // unused, but necessary
  		int maxY = (int)readSBits( bitSize );
  		width = maxX/20; //cause we're in twips
  		height = maxY/20;  //cause we're in twips
  		setPhysicalWidthDpi(72);
  		setPhysicalHeightDpi(72);
  		return (width > 0 && height > 0);
  	}
docs: Written by Michael Aird.