Audio and video bit-rate reduction

We address the problem of estimating limits of bit-rate reduction for audio and video information. Binary encoding of such signals is performed by a myriad of different techniques which we classify into two categories. The goal of "waveform" encoders is simply replication of waveforms, whereas "parameter" encoders attempt to extract and transmit only the basic features necessary for the specific application. Encoders are compared in terms of bits per Nyquist sample (η). Minimizing η requires utilization of source signal statistics and human perception. Accordingly, we discuss audio and video sources and their statistics, the salient properties of hearing and vision, and subjective assessment of quality. A review of the present state of waveform and parameter encoding is presented, summarized by graphs of η versus coder complexity for different qualities of reproduction. Current trends are then extrapolated, new directions anticipated and limiting values of η estimated. In summary, we predict that waveform encoders will be refined to the point where bit rates are nearly optimum, but highly variable. Dramatic reductions will only come about through sophisticated parameter encoding.