A digital video recorder (DVR) is a device that records an
input signal digitally, often to a
hard drive. The common consumer examples are TiVo and ReplayTV.
Consumer versions provide
features like trick play modes, live TV pause, and the ability to
get suggestions on programs in addition to your basic time-shifting.
Sometimes these devices are referred to as digital VCRs.
This is a misnomer,
as VCR stands for videocassette recorder. While it would be
possible to build a cassette-based
DVR, the effort would lose most of the benefits of current DVRs,
such as random access.
DVR type products have application beyond the consumer sphere, however;
the random access ability
makes them ideal for applications in the security industry,
video conferencing,
and even just recording a meeting. Due to their digital nature,
the recording medium doesn't
wear out slowly, unlike a tape left in a security system for a month or two.
In addition, more precise pausing is possible, as well as digital zoom capabilities.
It would be possible for such a unit to stream video to a PC on the same network as it.
In addition, large backup tapes could be used to back video up digitally.
Further more, the user interface on such a unit can be made much more user-friendly,
with online help and tutorials. Of course, for those who wish to pirate content, some of these abilities makes it
easy to copy pay per view and other television events, which is why the consumer versions seem to
be carefully restricted in their capabilities.
All DVRs that I am aware of rely on MPEG encoding for the video. As this is a lossy format, they are not terribly useful for video editing. However, provided that the video will not be decoded and then reencoded, this is not as much of a problem. Basic system architecture of a DVR seems to involve a microprocessor controlling dedicated (more or less) encoding and decoding chips. In some cases, the decoding chips are directly responsible for all facets of onscreen display, while in others they are just dedicated MPEG decoders. | 
