AVC to HEVC transcoder based on quadtree limitation

Following the finalization of the state-of-the-art High Efficiency Video Coding (HEVC) standard in January 2013, several new services are being deployed in order to take advantage of the superior coding efficiency (estimated at 50 % less bitrate for the same visual quality) that this standard provides over its predecessor: H.264 / Advanced Video Coding (AVC). However, the switch from AVC to HEVC is not trivial as most video content is still encoded in AVC. Consequently, there is a growing need for fast AVC to HEVC transcoders in the market today. While a trivial transcoder can be made by simply cascading an AVC decoder and an HEVC encoder, fast transcoding cannot be achieved. In this paper, we present an AVC to HEVC transcoder where decoded AVC blocks are first fused according to their motion similarity. The resulting fusion map is then used to limit the quadtree of HEVC coded frames. AVC motion vectors are also used to determine a better starting point for integer motion estimation. Experimental results show that significant transcoder execution time savings of 63 % can be obtained with only a 1.4 % bitrate increase compared to the trivial transcoder.