Adaptive rate control for MPEG transcoder

In MPEG, the input pictures can be coded in three different types, I, P and B. The three pictures require quite different numbers of bits because of different natures of their temporal processing. Hence, an intelligent bit allocation strategy should assign a target rate for a picture according to the picture´s type. Furthermore, for a given bit budget, the types of other pictures should also be taken into consideration. This implies a requirement of a prior knowledge of the picture organization (GOP). This requirement is not a problem for encoder as encoder can plan ahead the types of the pictures. A transcoder however has no such a priori knowledge about a picture´s type before actually processing the picture. This creates a difficulty in bit allocation for transcoder. This paper proposes a novel rate control scheme for MPEG transcoder that requires no a priori knowledge of the picture types. The experiments indicate that the picture target rates determined by the proposed rate control with and without a priori knowledge of the picture types are very close