Analysis of a joint video coding system

When studying the dynamic of joint video coding systems several issues need to be considered. Video quality estimation and multiplexing gain are usually based on simple scenarios, and in general consider separately networking and source coding. However, the key to successful implementation of VBR video transmission lies in the interface between video and network, specifically in the rules used to determine the bit rate that can be allowed into the network from each source. Once we have specified the interface we can produce models for the video bit rate under the chosen set of rate constraints and use these models to estimate network utilisation. In our work, the different encoders share the same bit rate control. This joint bit rate control allocates bits to each program in such a way that the sum of all the bit rates meets the negotiated connection parameters. Experiments have been performed keeping the global bandwidth constant. Video sources are grouped into three different classes, each one exhibiting different combined levels of spatial detail and amount of movement. Simulation results show that bandwidth gains/quality improvements are more significant when heterogeneous sources are multiplexed together, especially when video sources from classes C and B are present. Our current work includes video sequences with shot changes and variable GOP sizes. Developments are being done on the implementation of the protocol to improve the management of the communications between video encoders and multiplexer.