Scalable video coding and decoding methods, a scalable video encoder, and a scalable video decoder. The scalable video coding method includes receiving a GOP, performing temporal filtering and spatial transformation thereon, quantizing and generating a bitstream. The scalable video encoder for performing the scalable video coding method includes a weight determination block which determines a weight for scaling. The scalable video decoding method includes dequantizing the coded image information obtained from a received bitstream, performing descaling, inverse spatial transformation, and inverse temporal filtering on the scaled transform coefficients, thereby recovering video frames. The scalable video decoder for performing the scalable video decoding method includes an inverse weighting block. The standard deviation of Peak Signal to Noise Ratios (PSNRs) of frames included in a group of pictures (GOP) is reduced so that video coding performance can be increased.