This paper investigates a user attention model based on the visual rhythm analysis for automatically determining the region-of-interest (ROI) in a video. The visual rhythm, an abstraction of a video, is a thumbnail version of a fully video by a 2D image that captures the temporal information of a video sequence. Four sampling lines, including diagonal, anti-diagonal, vertical and horizontal lines, are employed to obtain four visual rhythm maps in order to analyze the location of the ROI from video data. Via the variation on visual rhythms, object and camera motions can be efficiently distinguished. The proposed scheme can extract the ROI accurately with very low computational complexity. The promising results from the experiments demonstrate that the moving object is effectively and efficiently extracted.

The MPEG-4/AVC/H.264 video coding standard adopts various coding schemes such as multiple reference frames and variable block sizes for motion estimation. Hence, MPEG-4/AVC/H.264 provides gains in compression efficiency of up to 50% over a wide range of bit rates and video resolutions compared to previous standards. However, these features result in a considerable increase in encoder complexity, mainly regarding to mode decision and motion estimation. The proposed algorithms use the stored motion vectors to compose the motion vector without performing the full search in each reference frame. Therefore, the proposed algorithms can obtain an average speed up ratio of four for encoding, thus benefiting from the prediction of the motion vector for the reference frames in advance and maintaining good performance. Any fast search algorithm can be utilized to further largely reduce the computational load.

In this paper, a fast motion estimation algorithm for variable block-size by using a motion vector merging procedure is proposed for H.264. The motion vectors of adjacent small blocks are merged to predict the motion vectors of larger blocks for reducing the computation. Experimental results show that our proposed method has lower computational complexity than full search, fast full search and fast motion estimation of the H.264 reference software JM93 with slight quality decrease and little bit-rate increase