1. A computer-implemented method, comprising: performing a discrete transform of a digital input signal according to one or more compression parameters, wherein said discrete transform generates a transformed signal comprising a set of transform coefficients; and generating a prediction of the size of a compressed signal that would be generated by an entropy encoding of the transformed signal by applying one or more formulae that model the behavior of entropy encoders to the set of transform coefficients; wherein said generating a prediction of the size of a compressed signal is performed without an entropy encoder performing actual entropy encoding of the transformed signal.