Research And Implementation Of Fast Mode Decision In To-H.264 Transcoding

With the development of digital video and multimedia technology, the series of MPEG and H.26x video coding standards have been widely used in different applications. In order to adapt to the diversity of terminal users and features of various networks, a compressed video bitstream is often transcoded from one format to another and shared by different users. The emergence of the new generation video coding standard H.264/AVC greatly contributes to the video's compression and transmission. The to-H.264 transcoding is becoming an active research topic and fast mode decision is one of the key techniques in the process of to-H.264 transcoding.In this paper, the status quo and key problems in transcoding technology is presented. The features of H.264 is analyzed and well compared with other coding standards. After going over several typical mode decision algorithms, novel fast mode decision methods are proposed considering two aspects, intra-frame and inter-frame prediction, when transcoding one format of video sequence to H.264 format.For intra-frame prediction, taking the advantage of direct coefficients conversion in the transform domain, IDCT and HT are saved. Two computationally different but highly correlated cost functions are employed as a criterion to choose the optimal intra-frame modes.For inter-frame prediction, the multiple modes and multi-frame reference features of H.264 are well considered to efficiently decide the block size to use. The proposed adaptive motion estimation search range, early-stop and top-down splitting methods contribute to high-speed transcoding with negligible PSNR drop and little bitrate increase.The proposed algorithms can be applied to transcoding several video formats to H.264. The system implemented at the end of this paper can transcode video encoded by H.263, MPEG-2, MPEG-4 simple profile to H.264.