It implements BSD-specific support for very old analog capture cards,
which are highly unlikely to be useful today. After being added in 2005,
there were never any commits to it beyond compilation fixes and generic
maintenance. There have also been zero trac tickets for this device, and
the only related web search result I found concludes that it does not
work.
The code also does some unacceptable things, like messing with signal
handlers and storing its state in global variables.
James Almer