Please see Audio/Video Streams for audio/video broadcasting of sessions and talks.
"Online participation" refers to the participation of individuals unable to attend the conference in-person. Non-attendees are only aware of conference proceedings if and when they are made available online.
Email is not a good real-time communication tool. IRC is a well-used instant messaging tool, but does not include support for audio/video teleconferencing. Freeswitch and Ekiga are good FLOSS teleconferencing tools.