Multi-program video compression using joint bit-rate control

Variable bit-rate compression (VBR) is known to be more efficient than constant bit-rate (CBR) compression. However, since most transmission media convey a constant bit rate, most applications use CBR compression. In multi-program applications, such as satellite and cable television, a technique called joint bit-rate control can be used. With joint bit-rate control the bit rates of individual programs are allowed to vary, but the sum of all bit rates is kept constant. Since a joint control is involved, the encoders should be geographically close. Joint bit-rate control is different from a technique called statistical multiplexing, which is proposed in combination with ATM networks. In this paper, the benefits of joint bit-rate control are studied. This study involves both a theoretical analysis and a verification with experiments. In the experiments a software simulation was used that included the two basic system aspects of joint bit allocation and variable bit-rate buffer management. Both theory and practice indicate that joint bit-rate control gives a significant gain even for a small number of programs. For instance, extra programs can be transmitted over the same channel, e.g. a satellite link, if joint bit-rate control is used.