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Digital Video is a type of Video recording system that works by using a Digital , rather than Analog , representation of the video signal. This generic term is not to be confused with the name '' DV '', which is a specific type of digital video targeted at the consumer market. Digital video is most often recorded on tape, then distributed on Optical Disc s, usually DVD s. There are exceptions, such as Camcorder s that record directly to DVDs, Digital8 camcorders which encode digital video on conventional analog tapes, and other high-end camcorders which record digital video on Hard Disk s or Flash Memory . The terms ''camera'', ''video camera'', and ''camcorder'' are used interchangeably in this article. HISTORY Early experiments with digital video were first accomplished throughout the 1960s by the research departments of entities such as the BBC and Bell Laboratories , both developing such to eliminate the introduction of noise and distortion on video feeds for television sent over the terrestrial microwave relay and coaxial cable circuits of the day. Also starting in the late 70s to the early 80s, several types of video production equipment, such as Time Base Corrector s (TBC) and Digital Video Effects (DVE) units (two of the latter being the Ampex ADO , and the NEC DVE), were introduced that would operate by taking a standard analog video input and internally digitizing it. 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 video 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 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 the expense, D-1 was used primarily by large Television Network s. It would eventually be replaced by cheaper systems using compressed data, most notably Sony's Digital Betacam , still heavily used as a field recording format by professional television producers. Consumer digital video first appeared in the form of QuickTime , Apple Computer 's architecture for time-based and streaming data formats, which appeared in crude form around 1990. 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 System s to be deployed wholly on desktop computers. TECHNICAL OVERVIEW Digital video cameras come in two different image capture formats: Interlace d 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 scanning digital video camera records each frame as distinct, with both fields being identical. Thus, interlaced video captures twice as many fields per second as progressive video does when both operate at the same number of Frames Per Second . This is one of the reasons video has a “hyper-real” look, because it draws a different image 60 times per second, as opposed to film, which records 24 or 25 progressive frames per second. Progressive scan camcorders such as the Panasonic DVX100 are generally more desirable because of the similarities they share with film. They both record frames progressively, which results in a crisper image. They can both shoot at 24 frames per second, which results in motion strobing (blurring of the subject when fast movement occurs). Thus, progressive scanning video cameras tend to be more expensive than their interlaced counterparts. (Note that even though the digital video format only allows for 29.97 interlaced frames per second 25 for PAL , 24 frames per second progressive video is possible by displaying identical fields for each frame, and displaying 3 fields of an identical image for certain frames. For a more detailed explanation, see the adamwilt.com link .) Standard , and PAL , which shoot at 30/1.001 (about 29.97) frames per second and 25 frames per second, respectively. Digital video can be copied with no degradation in quality. No matter how many generations a digital source is copied, it will be as clear as the original first generation of digital footage. Digital video can be processed and edited on an NLE, or Non-linear Editing station, a device built exclusively to edit video and Audio . These frequently can import from analog as well as digital sources, but are not intended to do anything other than edit videos. Digital video can also be edited on a personal computer which has the proper hardware and software. Using a NLE station, digital video can be manipulated to follow an order, or sequence, of video clips. Avid 's software and hardware is almost synonymous with the professional NLE market, but Apple’s Final Cut Pro , Adobe Premiere , Sony Vegas and similar programs are also popular. More and more, videos are edited on readily available, increasingly affordable hardware and software. Even large budget films, such as Cold Mountain , have been edited entirely on Final Cut Pro, Apple's non linear editing software. Regardless of software, digital video is generally edited on a setup with ample disk space. Digital video applied with standard 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, as the digital tapes can be erased and re-recorded multiple times, viewed on location without processing, and the tape stock itself is very inexpensive (about $3 for a 60 minute MiniDV tape, in bulk, as of December, 2005). 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 onto DVDs. While DV video is not compressed beyond its own codec while editing, the file sizes that result are not practical for delivery onto optical discs or over the internet, with codecs such as the Windows Media format, MPEG2, MPEG4, Real Media, the more recent H.264, and the Sorenson media codec. 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. As Of 2007 , the highest resolution demonstrated for digital video generation is 33 Megapixel s (7680 x 4320) at 60 frames per second (" UHDV "), though this has only been demonstrated in special laboratory settings. The highest speed is attained in industrial and scientific High Speed Camera s that are capable of filming 1024x1024 video at up to 1 million frames per second for brief periods of recording. INTERFACES AND CABLES Many interfaces have been designed specifically to handle the requirements of uncompressed digital video (at roughly 400 Mbit/s):
The following interface has been designed for carrying MPEG -Transport compressed video:
Compressed video is also carried using UDP - IP over Ethernet . Two approaches exist for this:
STORAGE FORMATS Encoding All current formats, which are listed below, are PCM based.
Tapes
Discs
SEE ALSO
EXTERNAL LINKS
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