Fast mode decision for KTA software

KTA (Key Technical Area) software is developed from the H.264 reference software by ITU-T VCEG to establish a common platform for developing high efficient techniques toward next generation video coding standard. With new techniques integrated, KTA software has achieved more than 20% improvement over H.264 in average. However, these new techniques not only bring high computations but also require multipass encoding optimization. In this paper, we propose two methods to significantly reduce mode checks in KTA software. First, the big inter mode skipping method skips modes of large block sizes if modes of smaller block sizes are better in an preprocessing. Second, we analyze the multi-pass encoding and propose the fast multi-pass mode decision method, which only checks the top modes in the first pass as candidates in the remaining passes. The proposed methods have reduced the encoding time as much as 80 percents with negligible PSNR loss and little bit rate increase.