Fast Intra/inter Mode Decision for Arbitrary Downsizing Video Transcoder Using H.264/AVC Standard

A fast macroblock mode decision scheme is proposed in this work for arbitrary downsizing video transcoder based on H.264/AVC. For macroblock to be re-encoded in downsized frame, the corresponding area in the pre-encoded frame is not aligned with the boundary of blocks when downsizing factor is arbitrary. The concepts of 'mapped block' and 'overlapped block' are proposed in this paper to represent the corresponding area. To reduce the computational complexity, method based on blocks or based on pixels is adopted according to the value of downsizing factor. We compared the compression performance and computational complexity of the proposed method with the full mode search method. The proposal can significantly reduce the computational complexity while the compression performance loss is slight.