Video decoding method and system thereof

A video decoding system for decoding a bit stream to a plurality of frames, comprising:

• a video decoder, for determining whether a size of a current picture is equal to that of a next picture according to the bit stream;
• a scaler, for scaling a corresponding reference frame for the next picture to generate a scaled frame when the size of the current picture is not equal to that of the next picture;
• and
• a storage unit, coupled to the video decoder and the scaler, the storage unit having a first buffer for storing the scaled frame, wherein at least a portion of a first frame originally stored in the first buffer is used;
• wherein when it is determined that the size of the current picture is not equal to that of the next picture, the next picture is encoded in the bit stream in a mode that the scaled corresponding reference frame is required for decoding the next picture.