NTSC
From MythTV Official Wiki
NTSC (National Television Standards Committee) Standard broadcast signal received by televisions in the United States. All television broadcasts in the United States must meet this standard. If a device is designed for NTSC, it will most likely not work with other television standards such as PAL, which is the standard broadcast signal used in Europe. However, there are certain types of equipment that support both standards.
Most NTSC broadcasts use scanning system M: 525/60 (or as it's now usually referred to, 480/30i),
