This paper presents mathematical frameworks on temporal predictiveprocessing in the MPEG video compression standard. Firstly, a coding gain is derived based on traditional prediction theories. The optimum ordering of three different picture types (I,P,B-pictures) is clarified according to image source characteristics. Secondly, a novel framework on the target bit assignment is presented with some experimental backgrounds. The solution consists of simple formulae, but brings drastic SNR gains to the conventional TM5 algorithm.