Digital video recorder

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(Redirected from Personal Video Recorder)

A digital video recorder (DVR) (also called Personal video recorder (PVR)) is a device that records video to a digital storage medium. The term DVR may be used to describe a piece of equipment such as a Personal Video Recorder (PVR) or a CCTV DVR. It may also be used to reference a function in a piece of equipment such as a digital video camera that has a DVR function built into it.

Television and video are terms that are sometimes used interchangeably, but differ in their technical definitions. Video is the visual portion of television, whereas television is the combination of video and audio modulated onto a carrier frequency (i.e., a television channel), so that multiple frequencies (i.e., multiple channels) may be transmitted at the same time.

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History

The first DVR was tested on July 8th, 1965, when CBS explored the possibilities of instant freeze-frame and rewind for sporting event broadcasts. Ampex released the first commercial hard disk video recorder in 1967. The HS-100 recorded analog video onto a digital hard disk and could store a maximum of only 30 seconds.

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Personal Video Recorder (PVR)

The personal video recorder (PVR) or digital personal video recorder, is a consumer electronics device that records television shows to a hard disk in digital format.

The two earliest consumer DVRs, ReplayTV and TiVo, were launched at the 1999 Consumer Electronics Show in Las Vegas. Although ReplayTV won the "Best of Show" award in the video category, it was TiVo that went on to much greater commercial success. The devices have steadily developed complementary abilities, such as recording onto DVDs, commercial skip, sharing of recordings over the Internet, and programming and remote control facilities using PDAs, networked PCs, or web browsers.

This makes the "time shifting" feature (traditionally done by a VCR) much more convenient, and also allows for "trick modes" such as pausing live TV, instant replay of interesting scenes, and skipping advertising. Most DVRs use the MPEG format for encoding analog video signals.

The two consumer DVR brands in the United States are the TiVo and DNNA's ReplayTV. In the UK TiVO has a small presence; Thomson, Topfield, Fusion, Pace and Humax also supply digital terrestrial (DTT) DVRs. BSkyB markets a popular combined EPG and DVR as [[Sky+]].

Many satellite and cable companies are incorporating DVR functions into their set-top box, such as with DirecTiVo, DishPlayer/DishDVR, Scientific Atlanta Explorer 8xxx, Motorola 6xxx from Comcast, Moxi Media Center by Digeo (available through Charter, Adelphia, Sunflower, Bend Broadband, and soon Comcast and other cable companies), or Sky+. In this case there is no encoding necessary in the DVR, as the satellite signal is already a digitally encoded MPEG stream. The DVR simply stores the digital stream directly to disk. Having the broadcaster involved with (subsidizing) the design of the DVR, and directly recording encrypted digital streams can lead to fancy features - like the ability to use interactive TV on recorded shows, pre-loading of programs; but can also lead to too much control by the broadcaster - like denying the ability to skip advertisements and automatically expiring recordings after a time determined by the broadcaster.

Other entrants into the market include products such as Microsoft's Media Center.

In 2003, the Yakima, Washington Police Department began using DVRs in their patrol cars to record the activities of officers and suspects. Since then, many other police departments have followed suit, due to the increased reliability and decreased cost compared to analog video systems.

There are ways to make one's own DVR using software and hardware available for Microsoft Windows, Linux and Macintosh operating systems. There are even efforts focused on using the popular Xbox gaming console as a DVR by adding a modchip.

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How a personal digital video recorder works

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Analog television

Analog television in NTSC, PAL or SECAM formats, analog cable, or regular VHS tapes use a signal that is fed directly to the electron beam within the television set. There are a number of details on how this is done, but in essence each line in each frame corresponds to a specific fraction of time within the signal.

To record an analog signal a few steps are required. A TV tuner card tunes into a particular frequency and then functions as a frame grabber, breaking the lines into individual pixels and quantizing them into a format that a computer can comprehend. Then the series of frames along with the audio (also sampled and quantized) are compressed into a manageable format, like MPEG-2, or WMF, usually in software. Some TV tuner cards like the DVR-250/350 or the TiVo chip deliver an MPEG-2 or other compressed stream directly to the computer, performing both the frame grabbing and compression in silico. This greatly reduces the load on the CPU allowing an overall cheaper implementation.

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Analog Broadcast Copy Protection

Many mass-produced consumer DVRs implement a copy-protection system called CGMS-A (Copy Generation Management System--Analog). This encodes a pair of bits in the VBI of the analog video signal that specify one of the following settings:

  • Copying is freely allowed
  • Copying is prohibited
  • Only one copy of this material may be made
  • This is a copy of material for which only one copy was allowed to be made, so no further copies are allowed.

CGMS-A information may be present in analog broadcast TV signals, and is preserved when the signal is recorded and played back by analog VCRs, which of course don't understand the meanings of the bits. But the restrictions still come into effect when you try to copy the tape onto a PVR.

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Digital television

Digital television is audio/visual signals that are broadcast over the air in a digital rather than analog format. Recording digital TV is generally a straightforward capture of the binary MPEG-2 data being received. No expensive hardware is required to quantize and compress the signal (as the television broadcaster has already done this in the studio). The MythTV DVR supports both European DVB signals and American ATSC signals while the HDTV Tivo supports only the ATSC signals. In the U.S., the FCC attempted to place a road-block before digital DVRs with its "Broadcast flag" regulation. Digital video recorders which had not won prior approval from the FCC for implementing "effective" digital rights management would have been banned from interstate commerce as of July 2005. The regulation was struck down on 6 May 2005.

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Satellite or Digital Cable

Recording satellite or digital cable signals on a digital video recorder is more complex than recording analog signals or broadcast digital signals. This is so because the MPEG-2 stream is usually encrypted to prevent people from viewing the content without paying for it (usually via subscription to a valid satellite decryption box and a decoder card).

The satellite or cable decoder box does two things. First it decrypts the signal. Second, it decodes the MPEG-2 stream into an analog signal for play on the television. In order to record cable/satellite digital signals you would need to get the signal after it is decrypted but before it is decoded (between steps one and two).

An alternative is that some satellite/cable decoder boxes have a FireWire port that can be connected to a computer. The MPEG stream could be relayed to the computer via this firewire port although there is as yet few, if any, current cards or devices that allow for a firewire connection to the computer from this box.

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DVR software

There is DVR software available for Linux, Macintosh and Windows for people who make their own homemade recorders.

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Linux

Three DVR applications for Linux are MythTV, Freevo and VDR; they use GPL open source software.

Brightbox, a consumer electronics device, uses an OEM Linux solution from SageTV.

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Macintosh

Elgato makes a series of DVR devices called EyeTV (400 / 500 / DTT etc.). The software supplied with each device (but available separately) is also called EyeTV. Elgato have recently released version 2.0 of their EyeTV software, with a redesigned interface, better program guide (built into the program) and a 'One Click' to iPod video feature.

Various rumor sites from the Mac rumors community have suggested Apple is working on PVR software, dubbed a 'TIVO-killer' and that this may be added to Front Row 2.0 and included with a 'Media Center' edition of the Mac Mini.

Apple provides applications in the FireWire software developer kit which allows any Macintosh with a FireWire port to record the MPEG2 transport stream from a FireWire equipped cable box. Only broadcast channels can be recorded as the rest of the channels are encrypted.

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Windows

Microsoft Windows has several free DVR applications including GB-PVR and MediaPortal. DScaler has also DVR support in works.

There also are several proprietary applications including SageTV, SnapStream Beyond TV, ChrisTV, Showshifter, Meedio (now a dead product - the company sold out to Yahoo), InterVideo WinDVR, Recordit Plus and the R5000-HD.

There is also a separate version of Microsoft Windows called Windows XP Media Center Edition which has DVR capabilities.

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Security application of DVRs

Digital video recorders configured for physical security applications record video signals from closed circuit television cameras for detection and documentation purposes. Many are designed to record audio as well. DVRs have evolved into devices that are feature rich and provide services that exceed the simple recording of video images.

Security DVRs may be categorized as being either PC based or embedded. A PC based DVR’s architecture is a classical personal computer with video capture cards designed to capture video images. An embedded type DVR is specifically designed as a digital video recorder with its operating system and application software contained in firmware or read only memory.

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Hardware Features

Hardware features vary between manufactures and may include but are not necessarily limited to:

  • Designed for rack mounting or desktop configurations.
  • Single or multiple video inputs with connector types consistent with the analogue or digital video provided such as coaxial cable, twisted pair or optical fiber cable. The most common number of inputs are 1, 4, 8, 16 and 32. Systems may be configured with a very large number of inputs by networking or bussing individual DVRs together.
  • Looping video outputs for each input which duplicates the corresponding input video signal and connector type. These output signals are used by other video equipment such as matrix switchers, multiplexers, and video monitors.
  • Controlled outputs to external video display monitors.
  • Front panel switches and indicators that allow the various features of the machine to be controlled.
  • Network connections consistent with the network type and utilized to control features of the recorder and to send and/or receive video signals.
  • Connections to external control devices such as keyboards.
  • A connection to external pan-tilt-zoom drives that position cameras.
  • Internal CD, DVD, VCR devices typically for archiving video.
  • Connections to external storage media.
  • Alarm event inputs from external security detection devices, usually one per video input.
  • Alarm event outputs from internal detection features such as motion detection or loss of video.
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Software Features

Software features vary between manufactures and may include but are not necessarily limited to:

  • User selectable image capture rates either on an all input basis or input by input basis. The capture rate feature may be programmed to automatically adjust the capture rate on the occurrence of an external alarm or an internal event
  • Selectable image resolution either on an all input basis or input by input basis. The image resolution feature may be programmed to automatically adjust the image resolution on the occurrence of an external alarm or an internal event.
  • Motion detection: Provided on an input by input basis, this feature detects motion detection in the total image or a user definable portion of the image and usually provides sensitivity settings. Detection causes an internal event that may be output to external equipment ans/or be used to trigger changes in other internal features.
  • Lack of motion detection. Provided on an input by input basis, this feature detects the movement of an object into the field of view and remaining still for a user definable time. Detection causes an internal event that may be output to external equipment and/or used to trigger changes in other internal features.
  • Direction of motion detection. Provided on an input by input basis, this feature detects the direction of motion in the image that has been determined by the user as an unacceptable occurrence. Detection causes an internal event that may be output to external equipment and/or be used to trigger changes in other internal features.
  • Routing of input video to video monitors based on user inputs or automatically on alarms or events.
  • Input, time and date stamping.
  • Alarm and event logging on appropriate video inputs.
  • Alarm and event search routines.
  • One or more sound recording channels.
  • Archiving routines.
  • Remote control routines.
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See also

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References

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External links

it:Personal Video Recorder he:PVR pl:Personal Video Recorder

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