Wednesday, February 22, 2006
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‚Äôt record the content unless they‚Äôve 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‚Äôve been employed as a security measure. DVRs have been used for police surveillance. They‚Äôre 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.