La perspectiva del Capital social desde la mirada de Pierre Bourdieu

formation onto the tape. Older videotape machines re- quired you to set the tracking control (measured by a small meter) on your source and or playback machines to optimize tracking. Most current video decks have

automatic track finding (ATF), an electronic system that lets the machine adjust itself for optimal playback. While tracking refers to the precise angle of each scan across the tape, skew refers to the tension of the tape around the video drum. Like tracking, skew can vary from machine to machine. As with tracking, older VCRs had manual skew controls, while today’s ma- chines adjust the skew automatically.

Digital Recording

Analog and digital are two ways of encoding informa- tion onto a storage medium. Conceptually, the difference between the two may be understood by considering analog to be a continuous process while digital is a discrete process. Analogvideotape record- ing occurs when the recorder receives electrical signals that are converted from, and analogous to, the light and audio waves that the camera and microphone pick up when recording. The recorder continuously tries to make a copy of those signals.

Digital encoding breaks the electrical signals down into small “pieces” or bitsand assigns a numeric description of the signal using 1s and 0s. This process is called sampling: taking a sample of each point along the analogous waveform and assigning that point a digital, or binary, code. (See Figure 7-8). The higher the sampling rate—that is, the more samples per second—the better: more points along the wave are used so they reproduce the original wave more ac- curately. The more bits used to code each point the better: more 1s and 0s give each point a more discrete, or unique, code. For example, many digital video (DV) formats can record audio with a sampling rate of 48,000 Hertz (Hz), or 48,000 times per second, meaning that each second of the audio waveform is broken down into 48,000 unique pieces. Addition- ally, these formats can record at 16 bits, meaning that a string of 16 1s and 0s is assigned to each of those 48,000 points per second. This is a very high-quality sampling and recording rate—even slightly better than is necessary for human hearing.

The device that samples the original analog wave- form and converts it to a binary digital signal is a

coder-decoder (codec). Different digital video for- mats have different codecs, and the devices are built into the cameras. For example, the mini-DV codec compresses the digital signal by a ratio of 5:1 (more on compression in the next section). To convert video that has been recorded in an analog format (e.g., VHS), stand-alone codec boxes are available that can be connected to the analog videotape recorder (VTR) for input into a digital source, such as a computer, to record the converted signal at output.

Compression

Digital video requires many megabytes (MB) of stor- age space. Uncompressed, one frame of NTSC video needs about 1 MB. That means one second (30 frames) needs about 30 MB. Even a multi-gigabyte (GB) hard drive can fill up fast at those rates! For this reason, most codecs also compress the signal: they re- move redundant information to reduce the file size. For example, if a newscaster sits in front of a still backdrop, that backdrop does not have to be recorded separately for each frame. Instead, the backdrop can be digitized once and the signal can be coded to include that same backdrop in each frame for however many seconds the clip lasts. Then only the newscaster’s movements must be recorded for each individual frame, reducing the amount of digital information re- quired for each frame while maintaining the image.

Compression may be either lossless or lossy. Loss- less compression schemes reduce the file size without any loss of detail. In the previous example, if neither the backdrop nor the newscaster is recorded with any

Figure 7-8 Sampling involves the selection of many points each second along a waveform and assigning each point a binary code of 1s and 0s; here, 16-bit sampling assigns a string of 16 1s and 0s to each point.

148 Chapter 7: Part One: Technical Editing Basics

loss of resolution and at a full frame rate (30 fps), the compression is lossless. However, it is sometimes desir- able to compress a file even more, particularly for de- livery over the Internet to people who do not have very high-speed connections. To accomplish this, lossy compression is necessary: removing additional infor- mation to reduce the file size considerably. In our ex- ample, the newscaster’s segment could be reduced from, say, a full DV 720 × 480 pixels to just 320 × 240 pixels. The number of bits recorded per pixel could be cut, reducing some color and brightness information. The frame rate could be cut in half to 15 fps, discard- ing every other frame so that the remaining frames each hold on the screen for two frame counts. The au- dio could be cut down by resampling from 48,000 Hz to 22,000 Hz, and the bit rate could be cut in half from 16 to 8. All this compression seriously reduces the file size, but on playback the viewers see a smaller, jerkier image with tinnier sound because both video and audio fidelity have been lost.

It should be noted that audio information does not require nearly the storage space that video information requires. You can download the audio file of a favorite three-minute song in a second, but downloading the three-minute music video of that song takes longer. Because audio requires less file space than video, com- pressing audio does not result in as much savings as compressing video. For this reason, some content cre- ators choose to leave the audio uncompressed for full fidelity sound even when they compress video. That way, the viewers can at least hear high-quality audio even if they have to watch small, jerky video.

A number of different compression systems are available. New systems are constantly being tested to improve video quality while decreasing the space re- quired after compression. Some still cameras that also record short video clips use a lossy compression sys- tem developed by the Joint Photographic Experts Group (JPEG) called Motion-JPEG. Common DVDs use a lossless scheme created by the Moving Pictures Expert Group (MPEG) called MPEG-2, which reduces video to about 20% of its original file size. That same group has developed a newer com- pression algorithm called MPEG-4, which is sup- ported by all four Internet media players: MoviePlayer, QuickTime, RealPlayer, and Flash.

For video editing, most professional software offers a variable compression rate that allows for different levels of quality. A high-compression mode (smaller file size) is used for doing offline edits, which increases the speed of the process and reduces the amount of storage needed, but greatly lowers the quality. A low- compression mode (larger file size) is used for online editing where the edited master file is high resolution, suitable for broadcast or high-quality storage, such as DVD or professional digital tape.

Digital Videotape

A number of digital videotape formats are on the mar- ket, including DigiBeta, DVCam, DVCPro, and digi- tal HDTV. While each has its unique characteristics, such as the width of the tape, the angle and speed with which the video head passes across the tape, the place- ment of the video fields on the tape, and the method for recording audio, all the formats share some com- mon characteristics. Here we’ll use one popular digital video (DV) format as an example to explore a bit more detail:mini-DV.

Mini-DV is the low-cost format of choice for many consumers, as well as prosumers and even some profes- sionals. The audio and video recording is excellent and, as with all digital formats, tape dubbing has no

generation loss. This format features a very small vid- eotape cassette (the tape is just 1/4-inch wide, or 6 mm), thus allowing for very small camcorders. Tapes consist of a plastic ribbon covered with a metal oxide that is magnetized to record the digital signal. VCRs that play and record mini-DV range from inexpensive camcorders to sophisticated units with many features. (See Figure 7-9.)

Figure 7-9 This DV player/recorder has time-based sta- bility and is used to feed digital nonlinear editing systems. (Courtesy of JVC)

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