Virtual reality 360-degree video is now widely used in various fields. However, the huge amount of data caused by its high resolution increases the coding complexity. While the existing video coding framework, such as HEVC, is not optimized according to the characteristics of virtual reality video, in order to accelerate the speed of intra-mode decision process in video coding, a new algorithm is proposed in this paper. Each virtual reality 360-degree video frame is divided into two regions, namely the pole region and the equatorial region. The number of candidate modes in the pole region is reduced in advance according to the statistical distribution pattern of the modes, and intra-mode in the equatorial region is determined by the cart decision tree using the texture contrast of the coding unit. The experimental results show that compared with the original HM16.20, the proposed algorithm can save the coding time by 28.3%, while only increasing the bd-rate by 0.612%.
Burgeoning virtual reality technology allows people to experience the content of video authentically. In order to provide an immersive experience to user, virtual reality video needs higher resolution (4K and higher) and more data than traditional video, which increases the coding complexity extraordinary. In this paper, a fast intra mode decision algorithm based on the sum of region-directional dispersion is proposed. Based on the diverse degree of horizontal stretching in different latitude area, the relationship of the optimal intra prediction mode related to latitude area for coding units is obtained. A new metric named the sum of region-directional dispersion is defined to determine the mode selection interval, and the prediction mode where located the minimum sum of dispersion is used as the center mode of the selection interval. The optimal intra prediction mode is obtained by comparing it with other adjacent modes in the interval. Compared with the original reference software HM16.20, the proposed algorithm can reduce the time in coding by 28.5%, while BD-rate only increases by 1.0%.
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