Cx18 devices (cx23418)
The cx18 devices feature an on-board hardware MPEG2 encoder; the Conexant CX23418. Notable devices within this category are the Hauppuage HVR-1600 and Compro VideoMate H900.
The cx18 has its own wiki within the ivtv Project (from which much of the code was derived) here: http://www.ivtvdriver.org/index.php/Cx18.
This driver is not yet fully functional, check the wiki for the current driver state.