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Digital Video.doc

  1. 1. Digital Video Clare R. Kilbane Digital Video Digital video refers to a technology used to record, and display moving images as binary data. Video in digital format is an increasingly popular means for delivering education and training content via CD-ROM and the World Wide Web because it can be easily integrated with other media in digital format including animations, audio, and text to create appealing multimedia materials. Analog versus Digital Video Formats Analog, the signal format most common before the rise of the digital signal format, is used with various technologies including telephone communications, broadcast radio, and television worldwide. Analog appliances record or transmit, information as a continuous electrical signal composed of electromagnetic waves. In analog video cameras waves are created by a charged coupled device or CCD. This device captures visual information and transforms it into an electrical signal that can be broadcast directly or recorded on magnetic tape. When analog video is sent from its source through the air, wire, or other network conduit, the electromagnetic signals weaken. During transmission signals run the risk of picking up vibrations from other sources that can result in errors or noise. To compensate for the weakened strength of signals at a distance, amplification is performed at various points during transit. The amplification of a weakened and sometimes error-filled signal often results in reduced signal quality and distortion. In contrast to the method used to record and transmit analog data, digital data travels as a series of discrete, high and low voltage pulses representing binary data. In digital video cameras, the charged couple device transmits high voltage pulses that represent a “1” and low voltage pulses that represent a “0.” Simple and discrete in form, these pulses can travel great distances with little deterioration in signal quality. When signal boosting is necessary, pulses can be replicated identically through signal regeneration. Digital signals do not pick up noise or vibrations in the way that analog signals do. Advantages of Digital Video Format over Analog Video Format The basic description of differences between analog and digital data formats accounts for several advantages of video recorded and transmitted in digital format over that in analog format. First, digital video makes more efficient use of storage and transmission space than analog video because it is composed of discrete pulses rather than continuous waves. In its natural, uncompressed state digital video requires less recording and transmission “space” than analog video. When it is compressed (a process that uses mathematical algorithms to eliminate extraneous data) it requires even less still. As a result, digital video requires less network bandwidth for transmission and less storage space for recording data. Extra space in network conduit is made available for multiple signals. Interactivity or two-way communications often results from using extra space. When storing digital video, increased efficiency results in better use of storage units such as cassettes, disks, hard drive space. Efficiency also results in digital video cassettes, cameras, and other equipment that are much smaller than those used for analog video. Because digital data can be stored efficiently, large amounts of data can be captured in less space. This results in the second advantage of digital video over analog video—superior quality. Digital video reproduces images that have greater accuracy to their original source than most analog video. Betacam, an expensive professional analog video, is the only analog standard that rivals the quality of digital video. Higher quality reproduction of moving images results from
  2. 2. Digital Video Clare R. Kilbane increased resolution, greater color rendition (the ability to produce accurate colors), and increased frame rate (the number of still images captured per second). For example, miniDV format captures 500 lines of horizontal resolution —a nearly 25% improvement over pictures recorded in the S-VHS or Hi-8 analog formats. Another advantage of digital video over analog video is its robust signal. This signal is free of problems encountered by an analog signal when it is transmitted over distances or copied. As a result, it is possible to dub multiple generations, or additional copies from other copies of the original source information without signal loss. Reproduction of digital video is less expensive because the process is does not require as much time or resources. One more significant advantage of digital video is its support for random access of stored information. This means that information recorded in digital format can be and usually is edited in a non-linear format. Unlike linear editing, where moving forward and backward through the medium is required before editing can occur, non-linear editing allows instant access anywhere in the data. This instant access saves time and allows greater creative control over material. For example, changing or switching one shot with another in nonlinear editing is a difficult proposition—re-editing of the entire piece is required to change even one frame. But when editing video in nonlinear format, it is easy and takes little time to both insert and remove video clips. Non-linear editing also makes it easy to link portions or clips of video together with transitions like dissolves and fades. It also makes it easier to modify the data and add special effects such as picture in picture and colored filters. Although it is possible to digitized analog video and edit this video using non-linear editing, this process requires special equipment and results in the degradation of video quality. Nonlinear editing systems work easily and fluidly with digital video requiring no special equipment and preserving video quality. Technological Advances in the Digital Video Continual technological advances resulting in improved compression rates, network bandwidth, software usability, and equipment costs have contributed to the growing preference for digital video as well. These advances influence every aspect of digital video production from the recording of video content, to its capture, production, and output on disk, tape, CD or the Web. As a result, users at every skill level—from beginners to professionals—are experiencing increased accessibility to the medium and the advantages it offers in the way of quality, usability, and compatibility. Progress in the hardware industry is steadily improving the performance of video capture cards, computer ports, processors and other devices associated with digital video. The improvement of the information transfer rates, (the speed of sending information from a user to a device that controls it) cameras, microprocessors, and media drives (special hard disks used to store video data) continually speed up the amount of time required to produce video. In large commercial video production houses, where time is money, speed increases have shortened production times resulting in increased profitability. Amateurs have also appreciated the ability to create small video clips without large investments of time. It is becoming more common for individuals to create and edit their own home videos on personal computers—an activity previously limited to professionals with expensive, fast, equipment. This progress has been accompanied by the creation of more efficient compression algorithms, called “codecs” (a word that refers to the coding and decoding that occurs in compression). By using various codecs to compress digital video, large, high-quality files can be reduced for storage and
  3. 3. Digital Video Clare R. Kilbane transmission. The development of more sophisticated compression algorithms has led to both a decrease in the file storage space required for storing digital video and the power of hardware for playing it. Software programs such as Terran’s Media Cleaner Pro, have made it easier to determine appropriate codecs for video depending on the method by which they will be stored and transferred. The popularity of digital video is also related to the physical expansion of global and local network infrastructures. The network expansion that promises the most dramatic impact on the use of digital video by the masses (specifically for entertainment purposes) is the placement of broadband networks in residential neighborhoods. Here, narrowband access through telephone lines (rates less than 1.5Mbps) is being replaced by broadband access (rates at or beyond 1.4Mbps) enabled by cable and digital subscriber lines (DSL). These expansions could help to overcome the “bottleneck” or slow-down caused when information travels from the broadband internet to narrowband residences and enable video use. At the moment, networks of all sizes are having difficulty keeping up with growing demands for bandwidth. If network bandwidth fails to meet the growing need for digital video, its increasing popularity as a medium for education and training on the Internet will likely wane. Groups who fear the Internet’s ability to support the increasing use of digital video have begun to install dedicated wide area networks (WANs). One such network, called the Internet-2, has been in use by colleges and universities since February 1999. This network boasts transfer rates of up to 2.4 Gbps. It is becoming more and more common for businesses and corporations to install their own internal, dedicated high-speed networks called intranets. Corporate intranets are already providing education and training materials, including videos, for employees. In fact, many of the best examples of digital video training materials are being developed on intranets. Although the growth of these networks means support is provided for the applications of digital video, it is unfortunate that these resources are not accessible to the open public. The removal of private resources from the Internet and access issues for promise to be problems for the future uses of digital video. Software for recording and editing, and playing digital video is also improving dramatically. The increased usability of nonlinear digital editing software programs with graphical user interfaces (GUI) has made complex editing processes simple and enabled greater creative control over the medium. Nonlinear editing programs such as Apple’s “Imovie,” and Avid’s “Avid Cinema,” have lowered the technical skill required with creating digitalvideo. As a result, more individuals have begun using these programs, resulting in greater sales and declining product costs. Another type of software, that required for playing digital video files, sometimes called “plug-ins” or “players” are also becoming easier to use and more affordable (free in most cases). As a result, access of digital video on the Internet or CD-ROM easier and faster, and more affordable for the general viewing population. The Production Process The creation of digital video content generally involves several steps. First content is recorded in either digital or analog video signal. This signal is stored on a tape. Popular analog tape formats include VHS, S-VHS, Hi-8, and Betacam. Popular digital video formats include Sony’s DVCAM, HDCAM and DigiBeta, and Panisonic’s DVCPRO. The method of storing data on the tape is the main difference between the different tape formats. The source and the quality of the initial video content that is recorded will vary considerably. Source content may range from previously edited, broadcast-
  4. 4. Digital Video Clare R. Kilbane quality to raw, unedited images. Source content might be recorded directly through the camera to the tape or prerecorded. The techniques for shooting video vary depending on the purpose and use for this footage. Video that will be viewed in conventional ways (on a television or monitor) will likely be filmed in different ways. Second, video content is “captured” using a video capture card – an internal device within a computer that allows individuals to input video as binary data. Video capture cards range in quality correlated with their cost. Cards that support high video resolution, color rendition, and frame rates are more expensive and those with less resolution, color rendition, and smaller frame rates cost less. Users have many options when selecting nonlinear editing systems because they vary in sophistication, quality, and cost. Low-end systems, the type commonly used by amateurs or “enthusiasts,” can be constructed from integrating several basic computer components. These include a personal computer with a fast processor (Pentium II, 250Mhz or higher), video capture card , sound card, and SCSI (small computer systems interface) controller. In order to control this hardware and edit video, a simple video editing software program must be installed and configured. Apple’s IMac computer, marketed as a preconfigured, low-end, easy-to-use system represents one popular option. Middle range systems, the kind commonly used by low-budget production companies and schools, consist of the basic hardware and other equipment such as video decks, mixing boards, disk arrays, and recording equipment. More powerful software programs such as Adobe “Premiere” and “Dazzle” are the most commonly used software options. High-end, commercial, nonlinear editing systems, the kind used by large- scale production houses producing movies and television programs, consist of basic hardware components modified to work specifically with proprietary nonlinear editing software. Such systems are available from major multimedia companies including Media 100 and Avid. Third, video content is edited and saved as an uncompressed file. It is this step in the production process that marks the greatest advantage of digital video over analog video. Digital editing software programs such as “Adobe Premiere” and “Avid Xpress” allow nonlinear interaction with digital content. Editing video using a digital editing software program allows instant access to specific images that may be located anywhere in the video content. This process enables greater creative control over the editing process. Transitions, titles, and special effects can be easily inserted and audio can be mixed seamlessly and simultaneously. Although the output of digital video is a linear sequence, for example, a series of images edited together to tell a story, constructing it in a non-linear process facilitates creativity and spontaneous decision making about content. Once edited, the video image is saved as an uncompressed file. Because uncompressed files are often incredibly large (often exceeding two gigabytes for four minute video clips), available hard drive space and operating system limitations on the size of files able to be written to hard drive space often complicate this process. Several standard file formats are commonly used for uncompressed files. These include Apple’s Quicktime (.mov, moov) and Video for Windows (.avi). Finally the content is compressed for distribution and delivered to the viewer. Data compression transforms a data into a code that is smaller than original code. Methods of coding data vary significantly and are evolving steadily. Perhaps the most significant difference in data compression processes exists between the lossy compression and the loss-less compression schemes. Lossy compression, the kind used in video and audio compression, discards
  5. 5. Digital Video Clare R. Kilbane some information during the compression process. Because video and audio are not an exact medium (meaning they can still communicate their message with some loss of information) the human ear and eye do not notice the loss of some data provided it is the right type of data. Loss-less compression, the kind used when exact information is required (like when sending text information) does not discard data. Compression performance is measured by the size of the output stream compared to the size of the input stream. Regardless of the compression process used for coding, a compressed file must be decoded before it can be viewed. Decompression is performed by software installed on the output computer. This software is referred to as “players” or “plug-ins.” This software may be preinstalled on a users’ computer operating system or web browser. If not, it must be packaged with digital video content. The standard compressions for coding and decoding video content are called “codecs.” The codec selected for distribution of digital video will vary based on the distribution medium and file format determined to be appropriate. Each codec is created for specific purposes. Professional video developers make decisions about appropriate codecs based on their knowledge of these codecs and the technological limitations of their intended audience. The delivery of digital video is undergoing an even more dramatic evolution than other aspects of digital video production. The most important development in the delivery of digital video content has been the development of streaming media. Streaming media is prerecorded or live content transferred to users on demand. Formats created by RealNetworks, Windows, Apple, and non- profit groups such as the Moving Pictures Expert Group are competing to become the standard in streaming media formats. Streaming media resides on a server or web server and can be accessed through links on html files situated throughout the Internet or through direct addressing. Streaming media turns digital video into fluid content that resembles other conventional media technologies such as broadcast and cable television. See also: streaming media, media convergance, broadband networks For further reading: Alesso, H.P. (2000). e-Video: Producing Internet video as broadband technologies converge. Boston: Addison-Wesley.