Research Of Rate Control Algorithm Based On H.263

In video communications, compressed video streams need to be transmitted over networks that have inconsistent and time-varying bandwidth requirements. To make the best use of available network resources at any time and guarantee a maximum level of perceptual video quality from the end-user's perspective, a certain rate control mechanism must be introduced into the video communication system. Over-rating the output of a video communication cause an undesirable traffic explosion and lead to congested networks. On the other hand, uncontrolled reduction of the output bit rate of a video coder leads to unnecessary quality degradation and inefficient use of available bandwidth resources. Rate control techniques must then be employed to regulate and control the output bit rates of video sources in the network to achieve the best trade-off between quality and bandwidth utilization.In the low-delay real-time video communications, rate control mechanism can use to adjust quantization parameter (Qp) to meet the channel rate, while keeping better picture quality and lower buffer delay. Rate control is often done at two layers: frame layer and macroblock (MB) layer. Sometimes frame layer rate control can't achieve the fine regulation of bitstream. Some low-delay applications such as video telephone and video conference need fine buffer adjustment and lower accumulated delay. Now macroblock layer rate control must be done.The work we have researched include several aspects as follows: (1) Several conventional rate control techniques are introduced, such as: SM3 rate control strategy, RM8 rate control strategy, TM5 rate control strategy and TMN8 rate control strategy. The advantage and disadvantage of those rate control strategy are analyzed. In those techniques, ITU-T H.263 TMN8 rate control strategy is one of the best techniques. In this paper, the theory of ITU-T H.263 TMN8 rate control strategy and how to perform are analyzed.