CCIR System M,[1][2][3] sometimes called 525–line, NTSC, NTSC-M, or CCIR-M,[4][5] is the analog broadcast television system approved by the FCC (upon recommendation by the National Television System Committee - NTSC)[6] for use in the United States since July 1, 1941,[7][8] replacing the 441-line TV system introduced in 1938.[8] It is also known as EIA standard 170.[9] System M comprises a total of 525 interlaced lines of video, of which 486 contain the image information, at 30 frames per second. Video is amplitude modulated and audio is frequency modulated, with a total bandwidth of 6 MHz for each channel, including a guard band.[10]
In 1965, Thailand decided to replace System M with 625-line CCIR System B, which started in 1967, adopting PAL at the same time.[12]
Circa 2003, the transition from analog System M to digital television broadcasting began, and in 2009 the United States ended high power analog transmissions. Other nations such as Japan, South Korea, and Taiwan also transitioned to digital while the Philippines remain on analog transmissions with digital simulcasts.