Digital video
Digital video is a type of video 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 NEC DVE) were introduced that operated by taking a standard analog 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 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 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, that made it in studios at their company.
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.[1] 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.
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 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 television 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[2]. 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 WxH.
Pixels have only one property, their color. The color of a pixel is represented by a fixed amount of bits. The more bits the more subtle variations of colors we can reproduce. This is called the color depth (CD) of the video.
An example video can have a duration (T) of 1 hour (3600sec), a frame size of 640x480 (WxH) at a color depth of 24bits and a frame rate of 25fps. This example video has the following properties:
pixels per frame = 640 * 480 = 307,200
bits per frame = 307,200 * 24 = 7,372,800 = 7.37Mbits
bit rate (BR) = 7.37 * 25 = 184.25Mbits/sec
video size (VS)[3] = 184Mbits/sec * 3600sec = 662,400Mbits = 82,800Mbytes = 82.8Gbytes
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 bits/sec, 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