ID3v2 FOOTER (optional)
To speed up the process of locating an ID3v2 tag when searching from the end of a file, a footer can be added to the tag. It is REQUIRED to add a footer to an appended tag, i.e. a tag located after all audio data. The footer is a copy of the header, but with a different identifier.
ID3v2 identifier "3DI" ID3v2 version $04 00 ID3v2 flags %abcd0000 ID3v2 size 4 * %0xxxxxxx