1. A system for voice activity detection (VAD) within a digitally encoded bitstream, the system comprising: a parameter extraction module configured to extract parameters from a sequence of coded frames from a digitally encoded bitstream containing speech; and a VAD classifier configured to operate with input of the digitally encoded bitstream to evaluate each coded frame based on bitstream coding parameter classification features to output a VAD decision indicative of whether or not speech is present in one or more of the coded frames.