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Residential DVRs or PVRs
Commercial DVRs
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DVRs explained |
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What is a digital video recorder (DVR, also known as a PVR or personal video recorder)? A DVR is a device that stores video data in a digital format for later playback. The main difference between a DVR and a VCR, is that a VCR uses an analog format to store data on a magnetic tape. A DVR stores its data in a digital format on a non-removable storage device, just as a computer stores its data to a hard drive. The amount of video data that can be stored on a DVR depends upon the size of the storage device. For residential applications this may be only hours of storage, while for commercial applications this may be months, or even years. |
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This article will examine the basic functionality of DVRs, as well as basic commercial and basic residential applications. Following articles will take a closer look at the different types of DVRs and typical applications, including commercial DVRs in CCTV (closed circuit television), and residential DVRs like Tivo.
Basic Functionality of DVRs |
A DVR is a stand-alone device that has an input for a video signal and an output for a TV or monitor. Inside the DVR is hardware, which will take the video signal and then write/store the signal to a hard drive. In most cases the video signal will be analog (except with digital cable or digital cameras), and so the DVR will also use hardware to convert the analog video signal into a digital format. This hardware will also compress the video signal into a smaller size for easier storage (just as computers compress files into .zip or .jar formats, DVRs use formats like MPEG and Wavelet). Pictured below are examples of PVRs or residential DVRs.
 Basic Residential DVRs |
Fig. 1 and Fig. 2 are examples of common residential DVRs. Both function in a similar manner, though they do have some different features. The main additional feature of Tivo is its subscription service. A Tivo DVR is connected between your cable or satellite signal and your TV, but it is also connected to your phone line. The phone line connection is so that Tivo will be able to download information about the programming that is scheduled to air in the following weeks. We will examine the value of this service in the following pages, but as a quick example imagine that you want to watch programs that feature Clint Eastwood, you would simply search on the name Eastwood, and Tivo would then generate a list of all the shows with Clint Eastwood in them. Fig. 2 is of a different type of DVR, one that is a cross between a DVD player and a DVR recorder. This DVR allows you to record, playback, and 'pause' your video, just like you can with Tivo. In addition, this type of DVR allows you to play DVDs, though it often will not have any of the added benefits of a subscription service. For a more in-depth look at residential DVRs click here.
 Basic Commercial DVRs |
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Fig. 3 and Fig. 4 are examples of common types of commercial DVRs. Fig. 3 is of a 'stand alone' DVR, which can be thought of as a cross between a residential DVR and a CCTV multiplexer. This type of DVR will have a more limited amount of storage space than the DVR in Fig. 4, and will in most cases have a more limited interface for viewing and searching video. The DVR in Fig. 4 looks more like a computer, and that is because it is, though it also has special hardware for converting analog signals to digital, and for compressing those signals for storage. The DVR in Fig. 4 also will typically have a much more advanced interface for working with the video data, including accessing the video remotely, motion detection, alarms, etc. For more information on commercial DVRs, click here.
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