An analog signal is any variable signal that's continuous in both time and amplitude. It differs from a digital signal because small fluctuations in the signal are meaningful. Digital signals use numbers for input, processing, transmitting, etc., rather than a continuous spectrum of values, so fluctuations in the digital signal can be ignored.There are three types of basic analog video formats: NTSC, PAL, and SECAM.Created in the United States, the NTSC format was named after the National Television System Committee, which approved the standard in 1953. This format is used primarily in North America and Japan.NTSC has a vertical resolution format of 525 total lines and a 59.95 Hz refresh frequency.NTSC replaced a system from the CBS network, which was later used by the National Aeronautical Space Administration (NASA) to broadcast pictures of astronauts in space.PAL was developed in 1967 by German engineer Walter Brunch at communications company Telefunken in Germany.PAL, which is short for “phase-alternating line,” “phase alternation by line,” or “phase alternation line,” is a color encoding system used in broadcast TV systems principally in Europe, the Middle East, and India.Cinema films are typically recorded at 24 f/s. When played back using PAL's 25 f/s formatting, films run 4 percent faster. While this is virtually unnoticeable (except that the soundtrack plays at a slightly higher pitch), movies run in PAL countries run for 4 percent less time than NTSC films.PAL is often used to refer to a 625-line, 50 Hz refresh frequency TV system.SECAM, short for “séquentiel couleur avec mémoire” in French, which means “sequential color with memory,” was invented by French television engineer Henri de France in 1956. The standard was adopted in France in 1967.SECAM differs from PAL and NTSC by the way the R(red)-Y(luminance) and B(blue)-Y signals are carried. First, SECAM uses frequency modulation to encode chrominance information on the subcarrier. Second, instead of transmitting the red and blue information together, it only sends one at a time, and uses the information about the other color from the preceding line.Because SECAM only transmits one color at a time, it's free of the color artifacts present in NTSC and PAL, resulting from the combined transmission of both signals.SECAM was originally adopted by French and Belgium colonies, as well as Eastern European countries and the Soviet Union. With the fall of communism, and following a period when multi-standard TV sets became a commodity, many Eastern European countries switched to PAL.