S terminal output and ordinary composite video output are two main types of video output for today's wireless video products.

The S terminal is actually a five-core interface, which is composed of five core wires of two video brightness signals, two video chrominance signals and one common shielded ground wire (in fact, there are brightness and chrominance separators matched with it) . It is not difficult to see from its structure that it is a device used to separate the output of brightness and chroma. This design is mainly to overcome the mutual interference of brightness and chroma when the video program is composite output.

The luminance signal bandwidth of general broadcast television is 6MHz, while the domestic PAL color signal bandwidth is 1.5MHz. Composite video output is to place the chrominance sub-carrier signal of 4.43MHz wave frequency in the video luminance signal, and perform chroma demodulation during display output to filter the chrominance sub-carrier from the composite video signal, which may cause loss The frequency of 4.43MHz ± 0.75MHz in the brightness signal reduces the horizontal definition. In addition, the chroma subcarriers that are not completely filtered out may interfere with the luma channel, while the luma signal at the edge of 4.43MHz will enter the chroma demodulation circuit, and the two interfere with each other, reducing the broadcast quality. Separate output of brightness and chroma of S terminal can improve picture quality, which is why some people call it "high definition output".