Combined SNR and Temporal Scalability for H.264/AVC using Requantization Transcoding and Hierarchical B Pictures

Requantization transcoding is a fast technique for video bit-rate reduction. In our previous work, we proposed a hybrid architecture for the requantization of H.264/AVC bitstreams. In this architecture, the B pictures were open-loop transcoded. When B pictures are not used as reference for coding neighboring pictures, this is an acceptable approach, since the requantization errors, originating from the B pictures, can not propagate to other pictures. In this paper, however, we compare different transcoding methods in case the coded video streams are composed of hierarchical B pictures. Here, the necessity for compensating the accumulated requantization error in reference B pictures needs to be investigated. We show that extended compensation techniques result in trans-coded sequences that approach the rate-distortion optimal decoder-encoder cascade within 1 dB. Compensation of intra-coded macroblocks only is proven to be a low-complexity alternative, with only minor concessions in rate-distortion performance.