Object-based rate allocation with spatio-temporal trade-offs

This paper describes a bit allocation algorithm that can achieve a constant bit rate when coding multiple video objects (MVOs), while improving the rate-distortion (R-D) performance over the reference method for MPEG-4 object-based rate control. In object-based coding, bit allocation is performed at the object level and temporal rates of different objects may vary. The proposed algorithm in this paper deals with these two issues. We pay particular attention to maintenance of buffer occupancy levels and propose a new method for spatio-temporal trades-offs for object-based coding. In order to improve the coding efficiency, we also consider several new R-D coding modes. These modes are available at the encoder to determine the best R-D performance under different coding conditions and are chosen automatically. Simulation results demonstrate moderate improvements at low and high bit rates. One important key aspect of the proposed algorithm is that the actual coded bits in the proposed algorithm are similar to the target bits over a wide range of bit rates. Consequently, the proposed algorithm has not experienced the buffer overflow/underflow over the entire range of bit rates.