Steganography in streaming media differs from steganography in images or audio files because of the continuous embedding process and the necessary synchronization of sender and receiver due to packet loss in streaming media. The conventional theoretical model for image steganography is not appropriate for explaining the security scenarios for streaming media based stegosystems. In this paper, we propose a new information-theoretical model with two pseudo-random sequences imitating the continuous embedding and synchronization characteristics of streaming media based stegosystems. We also discuss the statistical properties of Voice over Internet Protocol (VoIP) speech streams through theoretical analysis and experimental testing. The experimental results show the bit stream consisting of fixed codebook parameters in speech frames is similar in statistical characteristics to a white-noise sequence. The relative entropy between the VoIP speech stream and the embedded secret message has been found to be zero. This leads us to conclude that the proposed streaming media based stegosystem is secure against statistical detection; in other words, the statistical measures cannot detect the existence of the secret message embedded in VoIP speech streams.