The extended header contains information that is not vital to the correct parsing of the tag information, hence the extended header is optional.
Extended header size | | $xx xx xx xx |
Extended Flags | $xx xx |
Size of padding | $xx xx xx xx |
Where the 'Extended header size', currently 6 or 10 bytes, excludes itself. The 'Size of padding' is simply the total tag size excluding the frames and the headers, in other words the padding. The extended header is considered separate from the header proper, and as such is subject to unsynchronisation.
The extended flags are a secondary flag set which describes further attributes of the tag. These attributes are currently defined as follows
%x0000000 00000000
x - CRC data present
If this flag is set four bytes of CRC-32 data is appended to the extended header. The CRC should be calculated before unsynchronisation on the data between the extended header and the padding, i.e. the frames and only the frames.
Total frame CRC | | $xx xx xx xx |
@author Eric Farng
@version $Revision: 1.7 $