Anatomy of V4L-DVB devices
A minimal device for DVB receiption at the PC consists of a DVB Frontend amd some FIFO Memory. This FIFO samples the MPEG2 Transport Stream delivered by the frontend and makes it accessible (e.g. by a port-interface, memory-mapped or a bus-interface like USB or IEEE1394) to the host processor.
PCI Cards with onboard MPEG Decoder
The Onboard Decoder makes these cards somewhat expensive.
In a SetTopBox the Frontend directly feeds the built-in hostprocessor (usually with onchip MPEG Decoder). These processors are mostly based on embedded ARM-, MIPS-, PowerPC-Cores with additional peripheral units like i2c-, IDE-, network-, Smartcardcontrollers, Demultiplexers, Decoders, Audio- and Videointerface.
STBs with interface to the PC
Have an integrated embedded processor with MPEG2 Decoder and are able to work standalone. You can connect your PC to record and play back DVB transmissions on your TV.