By T.G. Venkatesh

Digital techniques for transmitting video signals have become popular in the last few years, as several video compression standards, such as MPEG-1 and MPEG-2, have been finalized and adopted. In most standards, the output bitrate control is considered an important issue in video coding, since it significantly affects video quality and compression. In the existing rate control methods, the bit rate is controlled by varying the quantization step size, thereby reducing unwanted DCT coefficients to zero. Instead of computing these coefficients and then reducing them to zero, pruning techniques can be used to limit the computation of the coefficients to a point where the maximum number of bits allotted for the corresponding block has been reached.

The objective of this work is to increase the computational speed of the MPEG implementation. Towards this end, new, pruning based, fast rate control schemes have been proposed in this work. The proposed rate control algorithm for the MPEG increases the speed of implementation due to the reduction in computations achieved by the use of the pruning technique. Additionally, a pipelined architecture with two processors is used to increase the speed of implementation further by processing the various tasks concurrently. With efficient distribution of the execution of the different steps in the MPEG between a DSP and a PC and with the use of the pruning technique, the entire system has been found to achieve an increase in speed by a factor of more than two compared to the normal implementation of the MPEG on a single processor.