A digital video recorder (DVR) or personal video recorder (PVR) is a consumer electronics device or application software that records video in a digital format to a disk drive, USB flash drive, SD memory card or other local or networked mass storage device. The term includes set-top boxes (STB) with direct to disk recording facility, portable media players (PMP) with recording, recorders (PMR as camcorders that record onto Secure Digital memory cards and software for personal computers which enables video capture and playback to and from a hard disk. A television set with built-in digital video-recording facilities was introduced by LG in 2007, followed by other manufacturers.

DVR adoption has rapidly accelerated in recent years: in January 2006, ACNielsen recorded 1.2% of US households having a DVR but by February 2011, this number had grown to 42.2% of viewers in the United States.

History

Hard-disk based digital video recorders

Consumer digital video recorders ReplayTV and TiVo were launched at the 1999 Consumer Electronics Show in Las Vegas, USA. Microsoft also demonstrated a unit with DVR capability, but this did not become available until the end of 1999 for full DVR features in Dish Network's DISHplayer receivers. TiVo shipped their first units on March 31, 1999. ReplayTV won the "Best of Show" award in the video category with Netscape co-founder Marc Andreessen as an early investor and board member, but TiVo was more successful commercially. While early legal action by media companies forced ReplayTV to remove many features such as automatic commercial skip and the sharing of recordings over the Internet, newer devices have steadily regained these functions while adding complementary abilities, such as recording onto DVDs and programming and remote control facilities using PDAs, networked PCs, and Web browsers.

Hard-disk based digital video recorders make the "time shifting" feature (traditionally done by a VCR) much more convenient, and also allow for "trick modes" such as pausing live TV, instant replay of interesting scenes, chasing playback where a recording can be viewed before it has been completed, and skipping of advertising. Most DVRs use the MPEG format for compressing the digitized video signals.

Video recording capabilities have become an essential part of the modern set-top box, as TV viewers have wanted to take control of their viewing experiences. As consumers have been able to converge increasing amounts of video content on their set-tops, delivered by traditional ‘broadcast’ [ Cable, Satellite and terrestrial] as well as IP networks, the ability to capture programming and view it whenever they want has become a must-have function for many consumers.

;Digital video recorders tied to a video service

At the 1999 CES, Dish Network demonstrated the hardware that would later have DVR capability with the assistance of Microsoft software. Users would have to wait until June 1999 for simple time shifting capabilities in the 7100, rebranded as the DISHPlayer satellite receiver, which also included WebTV Networks internet TV. By the end of 1999 the Dishplayer had full DVR capabilities and within a year, over 200,000 units were sold.

In the UK, digital video recorders are often referred to as "plus boxes" (such as BSKYB's Sky+ and Virgin Media's V+ which integrates an HD capability, and the subscription free Freesat+ and Freeview+). British Sky Broadcasting markets a popular combined EPG and DVR as Sky+. TiVo launched a UK model in 2000, and while no longer on sale, the subscription service is still maintained. South African based Africa Satellite TV beamer Multichoice recently launched their DVR which is available on their Dstv platform. In addition to ReplayTV and TiVo, there are a number of other suppliers of digital terrestrial (DTT) DVRs, including Thomson, Topfield, Fusion, Pace Micro Technology, Humax, AC Ryan Playon and Advanced Digital Broadcast (ADB).

Many satellite, cable and IPTV companies are incorporating digital video recording functions into their set-top box, such as with DirecTiVo, DISHPlayer/DishDVR, Scientific Atlanta Explorer 8xxx from Time Warner, Total Home DVR from AT&T; U-verse, Motorola 6412 from Comcast and others, Moxi Media Center by Digeo (available through Charter, Adelphia, Sunflower, Bend Broadband, and soon Comcast and other cable companies), or Sky+. Astro introduced their DVR system, called Astro MAX, which was the first PVR in Malaysia. Sadly, it was phased out two years after its introduction.

In the case of digital television, there is no ''encoding'' necessary in the DVR since the signal is already a digitally encoded MPEG stream. The digital video recorder simply stores the digital stream directly to disk. Having the broadcaster involved with, and sometimes subsidizing, the design of the DVR can lead to features such as the ability to use interactive TV on recorded shows, pre-loading of programs, or directly recording encrypted digital streams. It can, however, also force the manufacturer to implement non-skippable advertisements and automatically expiring recordings.

In the United States, the FCC has ruled that starting on July 1, 2007, consumers will be able to purchase a set-top box from a third-party company, rather than being forced to purchase or rent the set-top box from their cable company. This ruling only applies to "navigation devices," otherwise known as a cable television set-top box, and not to the security functions that control the user’s access to the content of the cable operator. The overall net effect on digital video recorders and related technology is unlikely to be substantial as standalone DVRs are currently readily available on the open market.

Introduction of dual tuners

In 2003 many Satellite and Cable providers introduced dual-tuner digital video recorders. In the UK, BSkyB introduced their first PVR Sky+ with dual tuner support in 2001. These machines have two independent tuners within the same receiver. The main use for this feature is the capability to record a live program while watching another live program simultaneously or to record two programs at the same time, possibly while watching a previously recorded one. Kogan Technologies introduced a dual-tuner PVR in the Australian market allowing free-to-air television to be recorded on a removable hard drive. Some dual-tuner DVRs also have the ability to output to two separate television sets at the same time. The PVR manufactured by UEC (Durban, South Africa) and used by Multichoice and Scientific Atlanta 8300DVB PVR have the ability to view two programs while recording a third using a triple tuner.

Where several digital subchannels are transmitted on a single RF channel, some PVRs can record two channels and view a third, so long as all three subchannels are on two channels (or one).

In the United States, DVRs were used by 32 percent of all TV households in 2009, and 38 percent by 2010, with viewership among 18 to 40 year-olds 40 percent higher in homes that have them.

Integrated TV-set digital video recorders

Coordinates	52°30′″N44°27′″N
name	Integrated LCD DVR
type	LCD DVR
extended to	}}

Digital video recorders are often integrated in the LCD and LED TV-sets. These systems let the user simplify the wiring and installation, because they do not use ports (SCART or HDMI), and they only need to use only one device and power and the same remote control instead of two.

There are examples of security systems integrated into such DVRs, and thus they are capable of recording more input streams in parallel. Some of them include wireless ports such as (Bluetooth and WiFi), so they can play and record files to or from cellular phones and other devices. Such devices can also be used as disguised observation systems, displaying pictures or videos as typical store display.

VESA Compatible digital video recorders

name	VESA Compatible DVR
type	DVR
owner	Lorex Technology
extended to	}}

VESA compatible DVR are designed small and light enough to mount to the back of an LCD monitor that has clear access to VESA mounting holes (100x100mm). This allows users to use their own personal monitor to save on cost and space.

PC-based digital video recorders

Software and hardware is available which can turn personal computers running Microsoft Windows, Linux, and Mac OS X into DVRs, and is a popular option for home-theater PC (HTPC) enthusiasts.

NAS DVR

An increasing number of Pay-TV operators are offering their subscribers the ability to create their own digital recording platform capable of storing video, audio, photos, etc. These customizable hardware and software platforms enable subscribers to attach their own NAS (Network Attached Storage) hard drives or solid state/flash memory to set-tops which do not have their own internal storage. This minimizes an operator’s investment, while offering subscribers the flexibility to create a digital recording solution that meets their specific requirements.

One such product is DVR-Lite(™), a vertically integrated hardware and software platform from Advanced Digital Broadcast, available on its Set-Back Box, which allows external storage to added by subscribers.

Linux

There are many free DVR applications available for Linux, each released as free and open source software under the GNU General Public License:

MythTV

VDR

LinuxMCE

Freevo

A commercial and proprietary application called SageTV is available for most popular Linux distributions.

Mac OS

Elgato makes a series of digital video recording devices called EyeTV. The software supplied with each device is also called EyeTV, and is available separately for use on compatible third-party tuners from manufacturers such as Pinnacle, TerraTec, and Hauppauge.

SageTV provided DVR software for the Mac but no longer sells it. Previously sold devices support the Hauppauge HVR-950, myTV.PVR and HDHomeRun hardware with its DVR software. SageTV software also included the ability to watch YouTube and other online video with a remote control.

MythTV (see above) also runs under Mac OS X, but most recording devices are currently only supported under Linux. Precompiled binaries are available for the MythTV front-end, allowing a Mac to watch video from (and control) a MythTV server running under Linux.

Apple provides applications in the FireWire software developer kit which allow any Mac with a FireWire port to record the MPEG2 transport stream from a FireWire equipped cable box (for example: Motorola 62xx, including HD streams). Applications can also change channels on the cable box via the firewire interface. Only broadcast channels can be recorded as the rest of the channels are encrypted. ''FireRecord (formerly iRecord)'' is a free scheduled-recording program derived from this SDK.

Windows

There are several free digital video recording applications available for Microsoft Windows including GB-PVR, MediaPortal, and Orb (web-based remote interface).

There are also several commercial applications available including CyberLink, SageTV, Beyond TV, Showshifter, InterVideo WinDVR, the R5000-HD and Meedio (now a dead product - Yahoo! bought most of the company's technology and discontinued the Meedio line, and rebranded the software Yahoo! Go - TV, which is now a free product but only works in the U.S.). Most TV tuner cards come bundled with software which allows the PC to record television to hard disk. For example, Leadtek's WinFast DTV1000 digital TV card comes bundled with the WinFast PVR2 software, which can also record analog video from the card's composite video input socket.

Windows Media Center is a DVR software by Microsoft bundled with the Media Center edition of Windows XP, the Home Premium / Ultimate editions of Windows Vista, as well as most editions of Windows 7.

Source video

Television and video are terms that are sometimes used interchangeably, but differ in their technical meaning. 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) for delivery. Most DVRs can record both.

Analog sources overview

The first digital video recorders were designed to record Analog television in NTSC, PAL or SECAM formats.

To record an analog signal a few steps are required. 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, usually in software.

Analog broadcast copy protection

Many mass-produced consumer DVRs implement a copy-protection system called CGMS-A or ''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.

DVRs such as Tivo also detect and act upon analogue protection systems such as Macrovision and DCS Copy Protection which were originally designed to block copying on analog VCRs.

Digital sources overview

Recording digital signals is generally a straightforward capture of the binary MPEG 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).

DVD-based PVRs available on the market as of 2006 are not capable of capturing the full range of the visual signal available with high definition television (HDTV). This is largely because HDTV standards were finalized at a later time than the standards for DVDs. However, DVD-based PVRs can still be used (albeit at reduced visual quality) with HDTV since currently available HDTV sets also have standard A/V connections.

ATSC broadcast

ATSC television broadcasting is primarily used in North America. The ATSC data stream can be directly recorded by a digital video recorder, though many DVRs record only a subset of this information (that can later be transferred to DVD. An ATSC DVR will also act as a Set-top box, allowing older televisions or monitors to receive digital television.

Copy protection

The U.S. FCC attempted to limit the abilities of DVRs with its "broadcast flag" regulation. Digital video recorders that had not won prior approval from the FCC for implementing "effective" digital rights management would have been banned from interstate commerce from July 2005, but the regulation was struck down on May 6, 2005.

DVB

DVB Digital television contains audio/visual signals that are broadcast over the air in a digital rather than analog format. The DVB data stream can be directly recorded by the DVR. Autonomous devices (this is, that can be used without a computer/tablet) that can store in an external hard disk are called a telememory.

Digital cable and satellite television

Recording satellite or digital cable signals on a digital video recorder can be more complex than recording analog signals or broadcast digital signals. There are several different transmission schemes, and the video streams may be encrypted to restrict access to subscribers only.

A satellite or cable set-top box both decrypts the signal if encrypted, and decodes the MPEG stream into an analog signal for viewing on the television. In order to record cable or satellite digital signals the signal must be captured after it has been decrypted but before it is decoded; this is how DVRs built into set-top boxes work.

Cable and satellite providers often offer their own digital video recorders along with a service plan. These DVRs have access to the encrypted video stream, and generally enforce the provider's restrictions on copying of material even after recording.

DVD

Many DVD-based DVRs have the capability to copy content from a source DVD (ripping).

In the U.S. this is prohibited under the Digital Millennium Copyright Act if the disc is encrypted. Most such DVRs will hence not allow recording of video streams from encrypted movie discs.

Digital camcorders

A digital camcorder combines a camera and a digital video recorder.

Some DVD-based DVRs incorporate connectors that can be used to capture digital video from a camcorder. Some editing of the resulting DVD is usually possible, such as adding chapter points.

Some digital video recorders can now record to solid state flash memory cards (called ''flash camcorders''). They generally use Secure Digital cards, can include wireless connections (Bluetooth and Wi-Fi), and can play SWF files. There are some digital video recorders that combine video and graphics in real time to the flash card, called DTE or "direct to edit". These are used to speed-up the editing workflow in video and television production, since linear videotapes do not then need to be transferred to the edit workstation (see Non-linear editing system).

File formats, resolutions and file systems

DVRs can usually record and play H.264, MPEG-4 Part 2, MPEG-2 .mpg, MPEG-2 .TS, VOB and ISO images video, with MP3 and AC3 audio tracks. They can also display images (JPEG and PNG) and play music files (MP3 and Ogg).

Some devices can be updated to play and record in new formats.

Recordings from standard-definition television usually have 480p/i/576p/i while HDTV is usually in 720p/1080i.

DVRs usually record in proprietary filesystems for copy protection, although some can use FAT filesystems.

Applications

TV recording

TV DVRs generally uses the electronic programming guide (EPG).

Security

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 that was previously done through VCRs. A DVR CCTV system provides a multitude of advanced functions over VCR technology including video searches by event, time, date and camera. There is also much more control over quality and frame rate allowing disk space usage to be optimized and the DVR can also be set to overwrite the oldest security footage should the disk become full. In some DVR security systems remote access to security footage using a PC can also be achieved by connecting the DVR to a LAN network or the internet. videoNEXT also makes a NVR surveillance application for the Mac OS X. Some of the latest professional digital video recorders include video analytics firmware, to enable functionality such as 'virtual tripwire' or even the detection of abandoned objects on the scene.

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.

Hardware features

Hardware features of security DVRs vary between manufacturers 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, 2, 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.

Software features

Software features vary between manufacturers 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.

Compression methods determine quality of playback. H.264 hardware compression offers fast transfer rates over the internet with high quality video.

Motion detection: Provided on an input by input basis, this feature detects motion 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 and/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.

One or more sound recording channels.

Archival.

Commercial hopping. Rather than fast-forwarding through commercials, an undocumented feature of the TiVo box is that the user can reprogram the tab-to-end button by entering a sequence of buttons on the remote: SELECT-PLAY-SELECT-3-0-SELECT and listening for the confirming chimes that signal the feature has been activated (or deactivated). The tab-to-end button no longer jumps to the end of a recording when so activated: It skips 30 seconds, which is the length of U.S. commercials. In combination with the 8-second rewind button, most viewers can completely miss commercial breaks in programming.

Privacy concerns

Some digital video recorders which are designed to send information to a service provider over a telephone line, Internet, (or any other way) can gather and send real-time data on users' viewing habits.

The future of TV advertisements

Digital video recorders are also changing the way television programs advertise products. Watching pre-recorded programs allows users to fast-forward through commercials, and some technology allows users to remove commercials entirely. Half of viewers in the United States, for example, use DVRs to skip commercials entirely. This feature has been controversial for the last decade, with major television networks and movie studios claiming it violates copyright and should be banned.

In 1985, an employee of Honeywell’s Physical Sciences Center, David Rafner, first described a drive-based DVR designed for home TV recording, time-slipping, and commercial skipping. U.S. Patent 4,972,396 focused on a multi-channel design to allow simultaneous independent recording and playback. Broadly anticipating future DVR developments, it describes possible applications such as streaming compression, editing, captioning, multi-channel security monitoring, military sensor platforms, and remotely piloted vehicles.

The first DVR which had a built-in commercial skipping feature introduced in 1999 by ReplayTV at the Consumer Electronics Show in Las Vegas. In 2002 five owners of the ReplayTV DVR sued the main television networks and movie studios, asking the federal judge to uphold consumers' rights to record TV shows and skip commercials claiming that features such as commercial skipping help parents protect their kids from excessive consumerism. ReplayTV was purchased by SONICblue in 2001 and on March 2003 SONICblue filed for Chapter 11 bankruptcy after fighting a copyright infringement suit over the ReplayTV's ability to skip commercials. In 2007 DirecTV purchased the remaining assets of ReplayTV. A third-party add-on for Windows Media Center called "DVRMSToolbox" has the ability to skip commercials. There is a command-line program called Comskip that detects commercials in an MPEG-2 file and saves their positions to a text file. This file can then be fed to a program like MEncoder to actually remove the commercials.

Many speculate that television advertisements will be eliminated altogether, replaced by advertising in the TV shows themselves. For example, ''Extreme Makeover: Home Edition'' advertises Sears, Kenmore, Kohler, and Home Depot by specifically using products from these companies, and some sports events like the Sprint Cup of NASCAR are named after sponsors.

Another type of advertisement shown more and more, mostly for advertising TV shows on the same channel, is where the ad overlays the bottom of the TV screen, blocking out some of the picture. "Banners", or "Logo Bugs", as they are called, are referred to by media companies as Secondary Events (2E). This is done in much the same way as severe weather warnings are done. Sometimes these take up only 5-10% of the screen, but in the extreme, can take up as much as 25% of the viewing area. Some even make noise or move across the screen. One example of this is the 2E ads for ''Three Moons Over Milford'' in the months before its premiere. A video taking up approximately 25% of the bottom-left portion of the screen would show a comet impacting into the moon with an accompanying explosion, during another television program.

Because of this widely used new technology, advertisers are now looking at a new way to market their products on television. An excerpt from the magazine ''Advertising Age'' reads: "As advertisers lose the ability to invade the home, and consumer's minds, they will be forced to wait for an invitation. This means that they have to learn what kinds of advertising content customers will actually be willing to seek out and receive."

With ad skipping and the time-sensitive nature of certain ads, advertisers are wary of buying commercial time on shows that are heavily digitally video-recorded. However, technology today makes it possible for networks to insert ads dynamically on videos being played in DVRs. Advertisers could inject time-relevant ads to recorded programs when the program is viewed. This way the ads could be not just topical but also personalized to viewers interests. DirectTV in March 2011 signed an arrangement with NDS Group to enable the delivery of such addressable advertisement. It is believed that viewers prefer to forward ads, than to switch the channel. By switching channels viewers will have the probability of skipping the beginning of their program. Users might switch to a channel that is also showing ads. Having the ability to pause, rewind, and forward live TV gives users a chance to change the channel less times. Forwarding ads can have a later affect on the viewer. Ads that get the viewers attention will influence the viewers to rewind and watch what was missed.

Patent and copyright litigation

On July 14, 2005, Forgent Networks filed suit against various companies alleging infringement on , entitled "Computer controlled video system allowing playback during recording". The listed companies included EchoStar, Directv, Charter Communications, Cox Communications, Comcast, Time Warner, and Cable One.

Scientific-Atlanta and Motorola, the manufacturers of the equipment sold by the above mentioned companies, filed a counter-suit against Forgent Networks claiming that their products do not violate the patent, and that the patent is invalid. The two cases were combined into case 6:06-cv-208, filed in the United States District Court for the Eastern District of Texas, Tyler Division.

According to court documents, on June 20, 2006, Motorola requested that the United States Patent and Trademarks Office reexamine the patent, which was first filed in 1991, but has been amended several times.

On March 23, 2007 Cablevision Systems Corp lost a legal battle against several Hollywood studios and television networks to introduce a network-based digital video recorder service to its subscribers. However, on August 4, 2008, Cablevision won its appeal. John M. Walker Jr., a Second Circuit judge, declared that the technology "would not directly infringe" on the media companies' rights. An appeal to the Supreme Court was rejected.

In court, the media companies argued that network digital video recorders were tantamount to video-on-demand, and that they should receive license fees for the recording. Cablevision and the appeals court disagreed. The company noted that each user would record programs on his or her own individual server space, making it a DVR that has a "very long cord."

See also

10-foot user interface

Astro MAX

Boxee

Comparison of PVR software packages

Direct to disk recording

DTE (Direct To Edit)

DTVPal DVR

FAT32

Freeview+

Handheld television

HD media player

Hard disk recorder

HDMI

Integrated circuit

List of portable software#Recorders

Media PC

Media server (Consumer)

Moxi

MythTV

Network Video Recorder

ReplayTV

SubRip

Sky+

TiVo

Proprietary DVR

PVR-resistant advertising

Remote control

Remote storage digital video recorder

Time shifting

USB hard disk

USB On-The-Go

V+

Video server (Broadcast)

XBMC

Notes

References

Free-to-Air Television and other PVR Challenges in Europe, technical report of the European broadcasting union

External links

How DVR works.

How-to guides for setting up open source DVRs on your pc

Comparison Chart of PVR FLOSS Media Centers

Commercial skipping to cost $8 billion in TV ads this year?

Automatic Commercial Skip in Media Center

Commercial-skipping 'thieves' sue accusers - Fans of Sonicblue gear strike back at entertainment giants

Television Remixed: The Controversy over Commercial-Skipping

NorDig PVR Metadata Whitepaper

Technical Specification ETSI TS 102 323 V1.4.1 (2010-01)

Video recorder Category:Television terminology

ar:مسجل فيديو رقمي ca:Enregistrador digital de vídeo da:Digital videooptager de:Festplattenrekorder es:Grabador de video digital eo:Siliciskopo fr:Magnétoscope numérique ko:디지털 비디오 레코더 it:Videoregistratore digitale he:PVR pl:Personal Video Recorder pt:DVR sv:Personal Video Recorder zh:数字视频录像机

A video recorder may be any of several related devices:

Digital video recorder (DVR); Personal video recorder (PVR)

DVD recorder

Videocassette recorder (VCR)

Video tape recorder (VTR)

da:Videooptager ko:영상 신호 기록 장치 ja:ビデオ信号記録装置 zh:攝錄機

Digital video is a type of digital recording system that works by using a digital rather than an analog video signal.

The terms ''camera'', ''video camera'', and ''camcorder'' are used interchangeably in this article.

History

Starting in the late 1970s to the early 1980s, several types of video production equipment- such as time base correctors (TBC) and digital video effects (DVE) units (two of the latter being the Ampex ADO, and the Nippon Electric Corporation (NEC) DVE) were introduced that operated by taking a standard analog composite video input and digitizing it internally. This made it easier to either correct or enhance the video signal, as in the case of a TBC, or to manipulate and add effects to the video, in the case of a DVE unit. The digitized and processed clip from these units would then be converted back to standard analog video.

Later on in the 1970s, manufacturers of professional video broadcast equipment, such as Bosch (through their Fernseh division), RCA, and Ampex developed prototype digital videotape recorders (VTR) in their research and development labs. Bosch's machine used a modified 1" Type B transport, and recorded an early form of CCIR 601 digital video. None of these machines from these manufacturers were ever marketed commercially, however.

Digital video was first introduced commercially in 1986 with the Sony D-1 format, which recorded an uncompressed standard definition component video signal in digital form instead of the high-band analog forms that had been commonplace until then. Due to its expense, D-1 was used primarily by large television networks. It would eventually be replaced by cheaper systems using video compression, most notably Sony's Digital Betacam (still heavily used as a electronic field production (EFP) recording format by professional television producers) that were introduced into the network's television studios.

One of the first digital video products to run on personal computers was ''PACo: The PICS Animation Compiler'' from The Company of Science & Art in Providence, RI, which was developed starting in 1990 and first shipped in May 1991. PACo could stream unlimited-length video with synchronized sound from a single file on CD-ROM. Creation required a Mac; playback was possible on Macs, PCs, and Sun Sparcstations. In 1992, Bernard Luskin, Philips Interactive Media, and Eric Doctorow, Paramount Worldwide Video, successfully put the first fifty videos in digital MPEG 1 on CD, developed the packaging and launched movies on CD, leading to advancing versions of MPEG, and to DVD.

QuickTime, Apple Computer's architecture for time-based and streaming data formats appeared in June, 1991. Initial consumer-level content creation tools were crude, requiring an analog video source to be digitized to a computer-readable format. While low-quality at first, consumer digital video increased rapidly in quality, first with the introduction of playback standards such as MPEG-1 and MPEG-2 (adopted for use in television transmission and DVD media), and then the introduction of the DV tape format allowing recording direct to digital data and simplifying the editing process, allowing non-linear editing systems (NLE) to be deployed cheaply and widely on desktop computers with no external playback/recording equipment needed. The widespread adoption of digital video has also drastically reduced the bandwidth needed for a high-definition video signal (with HDV and AVCHD, as well as several commercial variants such as DVCPRO-HD, all using less bandwidth than a standard definition analog signal) and tapeless camcorders based on flash memory and often a variant of MPEG-4.

Overview of basic properties

Digital video comprises a series of orthogonal bitmap digital images displayed in rapid succession at a constant rate. In the context of video these images are called frames. We measure the rate at which frames are displayed in frames per second (FPS).

Since every frame is an orthogonal bitmap digital image it comprises a raster of pixels. If it has a width of W pixels and a height of H pixels we say that the frame size is W''x''H.

Pixels have only one property, their color. The color of a pixel is represented by a fixed number of bits. The more bits the more subtle variations of colors can be reproduced. This is called the color depth (CD) of the video.

An example video can have a duration (T) of 1 hour (3600''sec''), a frame size of 640x480 ''(WxH)'' at a color depth of 24''bits'' and a frame rate of 25''fps''. This example video has the following properties:

pixels per frame = 640 * 480 = 307,200

bits per frame = 307,200 * 24 = 7,372,800 = 7.37''Mbits''

bit rate (BR) = 7.37 * 25 = 184.25''Mbits/sec''

video size (VS) = 184''Mbits/sec'' * 3600''sec'' = 662,400''Mbits'' = 82,800''Mbytes'' = 82.8''Gbytes''

The most important properties are ''bit rate'' and ''video size''. The formulas relating those two with all other properties are:

BR = W * H * CD * FPS VS = BR * T = W * H * CD * FPS * T (units are: BR in bit/s, W and H in pixels, CD in bits, VS in bits, T in seconds)

while some secondary formulas are: ''pixels_per_frame'' = W * H ''pixels_per_second'' = W * H * FPS ''bits_per_frame'' = W * H * CD

Regarding Interlacing

In interlaced video each ''frame'' is composed of two ''halves of an image''. The first half contains only the odd-numbered lines of a full frame. The second half contains only the even-numbered lines. Those halves are referred to individually as ''fields''. Two consecutive fields compose a full frame. If an interlaced video has a frame rate of 15 frames per second the field rate is 30 fields per second. All the properties and formulas discussed here apply equally to interlaced video but one should be careful not to confuse the fields per second rate with the frames per second rate.

Properties of compressed video

The above are accurate for uncompressed video. Because of the relatively high bit rate of uncompressed video, video compression is extensively used. In the case of compressed video each frame requires a small percentage of the original bits. Assuming a compression algorithm that shrinks the input data by a factor of CF, the bit rate and video size would equal to:

BR = W * H * CD * FPS / CF VS = BR * T / CF

Please note that it is not necessary that all frames are equally compressed by a factor of CF. In practice they are not, so CF is the ''average'' factor of compression for ''all'' the frames taken together.

The above equation for the bit rate can be rewritten by combining the compression factor and the color depth like this:

BR = W * H * ( CD / CF ) * FPS

The value (CD / CF) represents the average bits per pixel (BPP). As an example, if we have a color depth of 12bits/pixel and an algorithm that compresses at 40x, then BPP equals 0.3 (12/40). So in the case of compressed video the formula for bit rate is:

BR = W * H * BPP * FPS

In fact the same formula is valid for uncompressed video because in that case one can assume that the "compression" factor is 1 and that the average bits per pixel equal the color depth.

More on bit rate and BPP

As is obvious by its definition bit rate is a measure of the rate of information content of the digital video stream. In the case of uncompressed video, bit rate corresponds directly to the quality of the video (remember that bit rate is proportional to every property that affects the video quality). Bit rate is an important property when transmitting video because the transmission link must be capable of supporting that bit rate. Bit rate is also important when dealing with the storage of video because, as shown above, the video size is proportional to the bit rate and the duration. Bit rate of uncompressed video is too high for most practical applications. Video compression is used to greatly reduce the bit rate.

BPP is a measure of the efficiency of compression. A true-color video with no compression at all may have a BPP of 24 bits/pixel. Chroma subsampling can reduce the BPP to 16 or 12 bits/pixel. Applying jpeg compression on every frame can reduce the BPP to 8 or even 1 bits/pixel. Applying video compression algorithms like MPEG1, MPEG2 or MPEG4 allows for fractional BPP values.

Constant bit rate versus variable bit rate

As noted above BPP represents the ''average'' bits per pixel. There are compression algorithms that keep the BPP almost constant throughout the entire duration of the video. In this case we also get video output with a constant bit rate (CBR). This CBR video is suitable for real-time, non-buffered, fixed bandwidth video streaming (e.g. in videoconferencing).

Noting that not all frames can be compressed at the same level because quality is more severely impacted for scenes of high complexity some algorithms try to constantly adjust the BPP. They keep it high while compressing complex scenes and low for less demanding scenes. This way one gets the best quality at the smallest average bit rate (and the smallest file size accordingly). Of course when using this method the bit rate is variable because it tracks the variations of the BPP.

Technical overview

Standard film stocks such as 16 mm and 35 mm record at 24 frames per second. For video, there are two frame rate standards: NTSC, which shoot at 30/1.001 (about 29.97) frames per second or 59.94 fields per second, and PAL, 25 frames per second or 50 fields per second.

Digital video cameras come in two different image capture formats: interlaced and progressive scan.

Interlaced cameras record the image in alternating sets of lines: the odd-numbered lines are scanned, and then the even-numbered lines are scanned, then the odd-numbered lines are scanned again, and so on. One set of odd or even lines is referred to as a "field", and a consecutive pairing of two fields of opposite parity is called a ''frame''.

A progressive scan video camera records each frame as distinct, with all scan lines being captured at the same moment in time. Thus, interlaced video captures samples the scene motion twice as often as progressive video does, for the same number of frames per second.

Progressive-scan camcorders generally produce a slightly sharper image. However, motion may not be as smooth as interlaced video which uses 50 or 59.94 fields per second, particularly if they employ the 24 frames per second standard of film.

Digital video can be copied with no degradation in quality. No matter how many generations of a digital source is copied, it will still be as clear as the original first generation of digital footage.

Digital video can be manipulated and edited to follow an order or sequence on an NLE, or non-linear editing workstation, a computer-based device intended to edit video and audio. More and more, videos are edited on readily available, increasingly affordable consumer-grade computer hardware and software. However, such editing systems require ample disk space for video footage. Digital video recorded with standard consumer-grade DV/DVCPRO compression takes up about 250 megabytes per minute or 13 gigabytes per hour.

Digital video has a significantly lower cost than 35 mm film. The tape stock itself is very inexpensive — about $3 for a 60 minute MiniDV tape, in bulk, as of December, 2005. Digital video also allows footage to be viewed on location without the expensive chemical processing required by film. By comparison, 35 mm film stock costs about $1000 per minute, including processing.

Digital video is used outside of movie making. Digital television (including higher quality HDTV) started to spread in most developed countries in early 2000s. Digital video is also used in modern mobile phones and video conferencing systems. Digital video is also used for Internet distribution of media, including streaming video and peer-to-peer movie distribution.

Many types of video compression exist for serving digital video over the internet and on optical disks. The file sizes of digital video used for professional editing are generally not practical for these purposes, and the video requires further compression with codecs such as the Windows Media format, MPEG2, MPEG4, Real Media, and more recently H.264. Probably the most widely used formats for delivering video over the internet are MPEG4 and Windows Media, while MPEG2 is used almost exclusively for DVDs, providing an exceptional image in minimal size but resulting in a high level of CPU consumption to decompress.

While still images can have any number of pixels, the video community defines various standards for resolution. A path through devices that use incompatible resolutions may require that video be rescaled several times from capture to ultimate audience display.

, the highest resolution demonstrated for digital video generation is 33 megapixels (7680 x 4320) at 60 frames per second ("Ultra High Definition Television"), though this has only been demonstrated in special laboratory settings. The highest speed is attained in industrial and scientific high speed cameras that are capable of filming 1024x1024 video at up to 1 million frames per second for brief periods of recording.

Poster frame

A poster frames or preview frame is a selected frame of the video used as a thumbnail.

Interfaces and cables

Many interfaces have been designed specifically to handle the requirements of uncompressed digital video (at roughly 400 Mbit/s):

Serial Digital Interface

FireWire

High-Definition Multimedia Interface

Digital Visual Interface

Unified Display Interface

DisplayPort

USB

Digital component video

The following interface has been designed for carrying MPEG-Transport compressed video:

DVB-ASI

Compressed video is also carried using UDP-IP over Ethernet. Two approaches exist for this:

Using RTP as a wrapper for video packets

1-7 MPEG Transport Packets are placed directly in the UDP packet

Storage formats

Encoding

All current formats, which are listed below, are PCM based.

CCIR 601 used for broadcast stations

MPEG-4 good for online distribution of large videos and video recorded to flash memory

MPEG-2 used for DVDs, Super-VCDs, and many broadcast television formats

MPEG-1 used for video CDs

H.261

H.263

H.264 also known as ''MPEG-4 Part 10'', or as ''AVC'', used for Blu-ray Discs and some broadcast television formats

Theora used for video on Wikipedia

Tapes

Betacam SX, Betacam IMX, Digital Betacam, or DigiBeta — Commercial video systems by Sony, based on original Betamax technology

HDCAM was introduced by Sony as a high-definition alternative to DigiBeta.

D1, D2, D3, D5, D9 (also known as Digital-S) — various SMPTE commercial digital video standards

DV, MiniDV — used in most of today's videotape-based consumer camcorders; designed for high quality and easy editing; can also record high-definition data (HDV) in MPEG-2 format

DVCAM, DVCPRO — used in professional broadcast operations; similar to DV but generally considered more robust; though DV-compatible, these formats have better audio handling.

DVCPRO50, DVCPROHD support higher bandwidths as compared to Panasonic's DVCPRO.

Digital8 — DV-format data recorded on Hi8-compatible cassettes; largely a consumer format

MicroMV — MPEG-2-format data recorded on a very small, matchbook-sized cassette; obsolete

D-VHS — MPEG-2 format data recorded on a tape similar to S-VHS

Discs

Blu-ray Disc

DVD

VCD

See also

References

plug inns

External links

The DV, DVCAM, & DVCPRO Formats -- tech details, FAQ, and links

Standard digital TV and video formats.

Category:Film and video technology Category:Video signal Category:Television terminology

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