Statistical multiplexing

Abstract

A transmitter for transmitting a plurality of digital signals through a plurality of channels, the channels having a predetermined total allocated bitrate, includes a plurality of encoders each associated with one channel, a multiplexer for receiving the encoded digital signals and for transmitting the encoded signals as a stream of data, and operable for adjusting the distribution of the bitrate allocation between and among the encoded signals, and a processing device for providing an indication of a target quality and an actual quality for each channel and for causing the multiplexer to repeatedly adjust the distribution of the bitrate allocation in response to differences between the indicated actual quality and the indicated target quality for each channel so as to equalize differences between the actual and target quality across at least some of the channels. By grouping encoders together in "statistical multiplex groups", and making real time decisions about the bitrate requirements for those encoders, bitrate can be allocated to maximize picture quality for the group. For a variety of different picture sources in a statistical multiplex group, to achieve a target picture quality the bitrate requirements of each will vary with coding difficulty. Thus, a channel within the statistical multiplex group that is experiencing little difficulty in encoding its picture can free bits to channels that are having greater difficulty. The effect is to smooth the picture quality and subjectively improve it.

Dependencies are inferred from the claim text.