Digital video

Digital video is a type of video system that works by using a digital representation of the brightness and colour of each pixel of the image. Black and white digital video is also possible.

Digital video encoding formats:

• CCIR 601
• MPEG-4
• MPEG-2
• H.261[?]
• H.263
• H.264 a.k.a. MPEG-4 Part 10

Digital video tape formats:

• Betacam SX[?]
• Betacam IMX[?]
• D1[?]
• D2[?]
• D3[?]
• D5[?]
• D9 (aka Digital-S)[?]
• Digital Betacam[?]
• DV
• MiniDV
• DVCAM[?]
• DVC Pro, DVC Pro 50, DVC Pro HD[?]
• Digital8

Digital Camcorders come in two different data formats: interlaced and progressive scan. The interlaced cameras scan an image by alternating lines: the odd-numbered lines are scanned, and then the even-numbered, for each frame. For this reason interlaced cameras really only capture half the information in a given scene, but due to the persistence of vision, viewers typically do not notice any difference unless the object being filmed is moving quickly. When the object is moving quickly, its vertical edges appear jagged. Interlaced still photos have to be processed in a program like Adobe Photoshop to de-interlace them, making a half-sized image without the jagged edges. Progressive scan cameras scan the entire picture for each frame, producing a finer image than interlaced scan cameras, but typically cost a few hundred dollars more. An interlaced and a progressive MiniDV camera can use the same kind of tape.

"Standard" film stocks such as 16mm and 35mm record at 24 frames per second. In the U.S. digital video films at 29.97 "frames" per second (on the NTSC system); in Europe, on the PAL system, cameras film at 25 frames per second. In these cases, the term "frames per second" isn't technically correct although it is commonly used. Digital video doesn't have frames on a length of film; instead it scans the fields of an image, and a full scan of each of those fields is considered a "frame." For instance, the Canon XL-1 has 60 fields; a scan of each of those fields provides a complete picture; the camera completes this process of scanning each field 29.97 times each second. (There are various effects where fields can be ignored deliberately; even when every other field is ignored, the process still completes 29.97 times per second).

Provided that the video is retained in the same format (and not "recompressed", as often occurs when video is edited for distribution), digital video is a "lossless" format. That is, unlike analog sources, copies can themselves be copied without degradation in quality; a copy of the 256th generation footage will be as clear as the 1st generation footage provided that no frames have been dropped. On some capture cards or on some slower computers, the information being streamed in as the tape is rolling is coming in too fast for the computer to process, and the computer may drop a few frames. In this case the viewer typically will not notice anything visually, but the audio may "click" or "pop" briefly (for 1/30th of a second) which, oddly enough, typically will be noticed, especially in music. For this reason, it is important to process the video on equipment which can handle it.

Digital video can be processed 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 (an IEEE 1394 or Firewire card and, by 2001 standards, a fairly fast processor, as well as abundant disk space) and software (Adobe Premiere, iMovie, MGI Videowave, etc.)

Digital video has a high initial cost but a low cost afterwards, as the tapes can be viewed on location without processing, and can be reused on the spot. For instance, a take of a scene in 35mm would require the full attention of at least the cinematographer and director, and if both of them were happy with the take it would be sent to print. But if there is a problem that they did not notice, the print of that take is useless, as the film stock cannot be reused. Digital video is a favorite of independent film, as the cost is much lower. For instance, the cost of the total film stock for a feature film may easily be in the tens of thousands of dollars when using 35mm, but could be as low as a few hundred dollars for digital video, even if the crew doesn't reuse any tapes. Digital video is also faster to work with in filming, as the results of a take can be viewed instantaneously. For this reason, George Lucas has been using digital film in filming the new Star Wars movies, with digital video assist[?].

See also:

• Digital audio
• Digital film
• DVD
• Video coding
• Digital camcorder[?]
• Digital capture card[?]
• Video editing software
• Webcam
• Television
• Nyquist-Shannon sampling theorem
• Digital visual interface

Common misspelling and questions (FAQ)

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