From the ALSA wiki
Annodex is a way of embedding hyperlinks and timed metadata inside of Ogg Vorbis music, and Ogg Theora videos. There's a Mozilla Firefox extension for surfing annodex media at http://www.annodex.net/
For Debian folks there are two user packages in "unstable" that make it easy to try out *.anx annodex streams and a development package needed to build the AFE module for Firefox.
apt-get -t unstable install annodex-tools apt-get -t unstable install libannodex0 apt-get -t unstable install libannodex0-dev
This package contains tools that can be used to create and modify Annodex media. The Annodex media format allows annotations and indexes in streaming media and other types of continuous data, which can be used for hyperlinked video amongst other things.