Intraframe coding and decoding equipment are used in a communication network for digital video signals. Video signal sources which have various frequency deviations are transmitted by the communication network. Each of the intraframe coding and decoding equipment items has a locked sampling coding algorithm which is suitable for an input video signal with high frequency precision and a nonlocked sampling coding algorithm which is suitable for an input video signal with low frequency precision. It is determined whether or not the frequency precision (i.e., the frequency deviation of the sync signal) falls within a predetermined range. One of the coding algorithms is selected in accordance with a detection result. The coding algorithm can be selected in accordance with a decoding algorithm of a receiving-side equipment. Switching of the coding algorithms is performed simultaneously with switching of the clock signals of the locked and unlocked sampling clocks.