The SAA7146 is foremost simply a multimedia bridge to the PCI bus. It does not perform A/V decoding functions and, thus, does not have audio and video inputs, but rather provides a number of interface ports for standardized digital audio video streams. At a minimum, the SAA7146 can perform some processing on the video streams it is fed by providing scaling capabilities.
Essentially, the SAA7146 "enable[s] a wide variety of video and audio ICs to be connected to the PCI-bus thus supporting a number of video applications in a PC". The SAA7146 was well utilized and, not surprisingly, can be found configured on different PCI hardware devices such as analogue video framegrabbers, tv-cards, and A/V editing boards (see Saa7146 devices).
It is noteworthy to highlight that the SAA7146 was initially intended only as a multimedia interface for analog audio and video, however, the IC was adjusted to work with DVB by packing demodulated MPEG-2 Transport Stream data into the video interface lines of the IC. A large number of older generation DVB PCI card designs (such from TechnoTrend, Siemens, Hauppauge, KNC1 and TerraTec) did indeed made use of the SAA7146 as the PCI interface bridge. This hackish approach works surprisingly well in most setups, though, in some rare cases, a few end users have reported problems with high data loss. A more formal approach to providing DVB support was implemented in the SAA7146 chipset's direct successor, the SAA7134, as the later IC has a dedicated digital stream interface.