The category field in the BOS packet is a 16 byte text field (15 really, as it is zero terminated
in the bitstream itself). Its goal is to provide the reader with a short description of what kind
[http://www.shindiristudio.com/ web design] information the stream contains, eg subtitles, lyrics, etc. This would be displayed to the user,
possibly to allow to choose to turn some streams on and off.
This latter method may also be used if you already have an encoded Vorbis song
with no lyrics, and just want to add the lyrics without reencoding.