1. A method for predictive encoding comprising: quantizing a parameter vector of an input frame with a strongly-predictive codebook and a weakly-predictive codebook to obtain a strongly-predictive distortion and a weakly-predictive distortion; adjusting a correlation indicator based on a relative correlation of the input frame to a previous frame, wherein the correlation indicator is indicative of the strength of the correlation of previously encoded frames; and encoding the input frame with the weakly-predictive codebook unless the correlation indicator has reached a correlation threshold.