An interframe video data coding and decoding apparatus utilizes a differential amplitude suppression circuit in combination with a block encoder and a motion detector to non-linearly suppress amplitude values of interframe differential block data based on a motion detection threshold value determined by an encoding control circuit. The determined threshold value is based on the amount of encoded data being stored in a transmission buffer memory. The suppressed amplitude differential block data is added to corresponding blocks in a frame memory to update the contents of the frame memory during each frame of input video data. In another embodiment, vector quantization encoders are utilized to transmit a motion vector index with encoded frame differential data. In yet another embodiment, a time integral circuit integrates a continuous input video signal series by frame and writes the integrated frame signal into one of two frame memories, while interframe coding is performed on data stored in the other frame memory. Two transmission buffers are provided so that transmission can occur simultaneously with writing of the encoded interframe data into the buffer, by alternating switched connections of the two buffers.