A digital video recorder is basically similar to a VCR except that it records digital video and audio signals directly onto a hard drive instead of onto an analog video cassette. Technically, a DVR system can record from any standard digital video and audio source. However, most DVR systems are built to be tied into a cable television system, so adapting them to an over-the-air broadcast system can take some work.
Assuming you already have a DVR system, you will need some additional equipment to route the over-the-air broadcast signal to your DVR system. First, you will need an antenna capable of receiving digital broadcast signals. Then, you may need a digital encoder/decoder to translate the digital broadcast signal into a format that your DVR can work with, though some systems are able to translate the signals internally. Finally, you will likely need different types of cables to transmit the signals between your various devices. The specific cables you will need will depend on what kinds of TV and DVR equipment you're using.
If you don't already have a DVR system, all you really need is a basic desktop computer system. Your system will also need a video card capable of outputting digital video and audio in a format that your television will be able to display. The current standard as of 2011 is HDMI; however, there are several other digital formats and many people still have older analog television sets that use coaxial or composite video connections. Once you have an adequate computer setup, you need to purchase or otherwise acquire DVR software. There are many commercially available applications as well as several well-regarded open-source free applications. Among them are the for-profit SageTV and BeyondTV, as well as the open-source MythTV and Freevo.
You need to ensure that your DVR can read the digital video and audio source being sent to it from the antenna. The most foolproof way of doing this is by using a digital encoder/decoder between the antenna and the DVR. However, this isn't strictly necessary as many newer DVR software applications come with the appropriate codecs installed for reading incoming digital broadcast signals. Additionally, over-the-air broadcast signals are based on existing standards that should be consistent between broadcasters.
Digital video broadcast and recording is still a relatively new consumer technology. As such, there are a number of problems that are still being worked out. Among them are the various broadcast signal formats that may be used by broadcasters and may be subject to change as the digital broadcast techology advances. There are also user-side technology issues. Technically, just about any old computer can serve as a DVR; however, older models will be slower than newer computers or dedicated DVR systems. Home-built systems are prone to compatibility issues that the builder may not have anticipated, which is why many people opt for dedicated DVR systems. Dedicated DVR systems come with their own issues -- especially systems that come with subscription TV services such as satellite TV or cable.
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