Routines common to a number of multimedia tools. The library
originates from work on the RAT project: these are portions that are
not directly related to an audio tool and potentially useful
elsewhere like the bundled RTP beacon.

The beacon is designed to provide multicast connectivity information.
This is done by sending at a prescribed interval a short message via
RTP (a plain text string as it were). Then the normal RTP statistics
communicated via RTCP are used to track the performance of the group.