An efficient hierarchical VBR video coder over ATM networks

ATM, which has been recommended by the ITU as the transfer mode in broadband ISDN, supports the transmission of variable bit-rate (VBR) traffic via statistical multiplexing and assigns priorities to the transmitted signals. A new DCT-based hierarchical coding technique is developed for VBR video over ATM networks. Since the low DCT frequencies are more visually important than the high frequencies in a video frame, the coefficients are divided into a primary and secondary layer. The coefficients at the primary layer are coded by the MPEG standard, while those at the secondary layer are further divided into several subvectors, each of which is coded by vector quantization (VQ) technique. We present a bit rate allocation algorithm which determines how to allocate a given quota of bits among the subvectors at the secondary layer. Experimental results show that the hierarchical coding scheme produces high quality video signals with low bit rates in terms of the mean value of the signal-to-noise ratio (SNR). In addition, the burstiness of both the primary and secondary layers is significantly reduced, thereby facilitates video transmission over ATM networks