Drift-free switching of compressed video bitstreams at predictive frames
Two schemes are proposed to efficiently compress video contents into bitstreams that support drift-free switching at predictive frames. They are inspired by the original SP coding scheme presented in the early H.26L. First, we propose a Flex SP coding scheme in which the prediction signal of the SP frame is directly subtracted from the input without quantization and de-quantization. The decoded video quality of the Flex SP scheme is significantly improved when additional inverse discrete cosine transform (DCT) and post-filter are provided. Then, the Hybrid SP scheme is presented to further improve the quality of the display image, as well as the reconstructed reference, by defining two coding modes for each DCT coefficient. Moreover, a rate-distortion algorithm is proposed to determine the coding mode for each coefficient. The bitstreams generated by the two proposed schemes can be decoded successfully by a decoder that complies with MPEG-4 AVC/H.264. In addition, we also investigate how to choose the quantization parameters for switching. An empirical method is proposed to achieve a good tradeoff between high coding efficiency of SP frames and small size of switching bits.