Digital video

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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 discs, usually DVDs. There are exceptions, such as camcorders that record directly to DVDs, Digital8 camcorders which encode digital video on conventional analog tapes, and camcorders which record digital video on hard disks.

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

1 History
2 Technical overview
3 Interfaces and cables
4 Storage formats
5 See also
6 External links

[edit] History

Digital video was first introduced in 1983 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 networks. 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 systems to be deployed wholly on desktop computers.

[edit] Technical overview

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 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 so, 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 [or 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 film stocks such as 16 mm and 35 mm record at 24 or 25 frames per second. For video, there are two frame rate standards: NTSC, 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, 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 tapes can be 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 megapixels (7680 x 4320) at 60 frames per second ("UHDV"), though this has only been demonstrated in special laboratory settings [1]. 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.

[edit] Interfaces and cables

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

[edit] Storage formats

[edit] 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 and Super-VCDs
MPEG-1 used for video CDs
H.261
H.263
H.264 also known as MPEG-4 Part 10, or as AVC
Theora standardized but still in development. used for video over the internet.

[edit] Tapes

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

[edit] Discs

[edit] See also

[edit] External links

Digital Video magazine
The DV Show - Podcasting the Ins and Outs of Digital Video
IzzyVideo.com - Watch a Video Podcast about shooting better Digital Video
Adam Wilt's website, including the DV FAQ
Adam Wilt's explanation of how 24 progressive frames per second video is recorded to 29.97 interlaced frames per second
Home Video101 - Contains non vendor specific information for creating DVDs from home movies.

Digital systems
Logic gate \| digital circuit \| integrated circuit (IC)
Theory — boolean algebra/logic \| digital signal processing \| computer architecture
Applications — digital photography \| digital audio \| digital video
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v • d • e Industrial & home video media
Magnetic tape	VERA (1952) - 2 inch Quadruplex videotape (1956) - 1 inch type A videotape (1965) - 1/4 inch Akai (1967) - U-matic (1969) - Cartrivision (1972) - Video Cassette Recording (aka VCR) (1972) - V-Cord (1974) - VX (aka "The Great Time Machine") (1974) - Betamax (1975) - 1 inch type B videotape (1976) - 1 inch type C videotape (1976) - VHS (1976) - VK (1977) - SVR (1979) - Video 2000 (1980) - CVC (1980) - VHS-C (1982) - M (1982) - Betacam (1982) - Video8 (1985) - MII (1986) - D1 (1986) - S-VHS (1987) - D2 (1988) - Hi8 (1989) - D3 (1991) - D5 (1994) - Digital-S (D9) (199?) - S-VHS-C (1987) - W-VHS (1992) - DV (1995) - Betacam HDCAM (1997) - D-VHS (1998) - Digital8 (1999) - HDV (2003)
Optical discs	LaserDisc (1978) - Laserfilm (1984) - CD Video - VCD (1993) - DVD-Video (1996) - MiniDVD - CVD (1998) - SVCD (1998) - FMD (2000) - EVD (2003) - FVD (2005) - UMD (2005) - VMD (2006) - HD DVD (2006) - Blu-ray Disc (BD) (2006) - DMD (2006?) - AVCHD (2006) - Tapestry Media (2007) - Total Hi Def (2007) - HVD (TBA) - PH-DVD (TBA) - SVOD (TBA) - Protein-coated disc (TBA) - Two-Photon 3-D (TBA)
Grooved Videodiscs	Baird Television Record aka Phonovision (1927) - TeD (1974) - Capacitance Electronic Disc aka CED (1981) - VHD (1983)