Digital Video Recorders

A digital video recorder (DVR) records video in a digital format and stores it, most often on a hard disk. DVRs are also known as personal video recorders (PVRs). Two common DVRs are TiVo and ReplayTV, both of which were introduced in 1999. TiVo is perhaps the best-known DVR. DVRs have advanced to the point where they can offer many more options besides simply recording TV shows and saving them for viewing. DVRs can also record material onto DVDs and facilitate the sharing of recorded programs over the Internet. DVRs have a special appeal. Just like magic, with a DVR, viewers can pause a live TV program, cut out commercials, and replay programming instantly. DVRs have varying storage capacities. Recording capabilities range from 30 to 320 hours.

DVRs employ the MPEG format to encode video signals. They can be used to record programming from both analog and digital television sets. To record analog content, a TV tuner card is required. This card picks up the analog signal and processes image frames. During the processing, the lines of an image are broken down into pixels and put into a format the computer can read. The image frames, as well as the sound, are stored, usually in MPEG-2 or a WMP form, on the DVR.

Recording program content from digital television is a less complicated process. No special equipment is needed. The digital content is already compressed and stored in MPEG-2 form when the DVR receives it. This is done by the television broadcaster.

A large number of satellite and cable providers are integrating DVR options into their equipment. Motorola and Comcast, for instance, now offer set-top boxes with DVR functions. But recording from satellite or digital cable can be tricky. The MPEG-2 signal is often adjusted so that viewers can't record the content unless they've paid for it. To access the MPEG-2 stream, satellite and cable subscribers must purchase a decryption box and a decoder card. The box reads the signal and then decodes the MPEG-2 stream. It then translates the stream into an analog signal for viewing on TV. Another option for cable and satellite subscribers is the use of a FireWire port. This port can be hooked up to a computer. The MPEG stream can then be transmitted to the computer for recording.

DVRs are now used for other purposes besides personal recording. Interestingly enough, they've been employed as a security measure. DVRs have been used for police surveillance. They're also used to record signals from closed circuit TV cameras. Some DVR models offer security detection features, including alarm capabilities related to motion detection or video failure.