The invention relates to a video input decoder chip which comprises a digital direct frequency synthesizing module, a phase lock loop module, a power on reset module, a digital circuit module, a bandgap reference module, a V-I conversion module, a test end selection module and three signal processing channels, i.e. channel 1, channel 2 and channel 3, wherein, the channels comprise a signal source selection module, a clamp module, an automatic gain control module, an anti-alias filter and an analog-to-digital conversion module. The chip can process CVBS, Y / C and RGB signals, has strong noise suppression capability, generates a reference voltage and a clock interiorly, realizes the high integration degree, needs no external decoupling capacitor, greatly reduces the system area and the complexity degree and improves the signal processing efficiency.