Video conferencing oriented low-complexity coarse-level mode-mapping based H.264/AVC to H.264/SVC spatial transcoding

As an extension of H.264/AVC, Scalable Video Coding (SVC) provides flexible adaptation to heterogeneous networks and end-users, which provides great scalability for applications such as video conferencing. However, due to the existence of legacy H.264/AVC-based systems, transcoding between AVC and SVC becomes necessary. Currently there are few works done on AVC-to-SVC spatial transcoding, and re-encoding method involves high computational cost. This paper proposes a low-complexity coarse-level mode-mapping based AVC-to-SVC spatial transcoder for video conferencing applications. First, to omit unnecessary motion estimations (ME) for layers with reduced resolution, an ME skipping scheme based on AVC mode distribution is proposed with an adaptive search range. After that an adaptive coarse-level mode-mapping method is presented for fast mode decision. Finally, motion vector (MV) refinement is introduced for further lower-layer time reduction. As for the top layer, direct encapsulation is proposed to preserve better quality and another scheme involving inter-layer predictions is also provided for bandwidth-crucial applications. Simulation results show that proposed transcoder achieves up to 90.6% time reduction without significant coding efficiency loss compared to re-encoding method.