【摘要】：隨著人們對視頻服務消費水平的提高,人們也熱衷于追求高分辨率視頻。視頻分辨率的增加,給視頻的存儲和傳輸帶來了很大的挑戰(zhàn)。目前,如何使編碼產生的碼流符合帶寬要求是視頻編碼中的研究熱點。碼率控制成為了解決此問題的關鍵,碼率控制通過控制編碼量化參數,使輸出碼率接近帶寬大小,充分利用帶寬。本文通過研究新一代視頻編碼標準HEVC的幀內碼率控制算法,提出了相關的改進算法和策略。主要包括兩部分:1)HEVC幀內碼率控制算法并沒有考慮視頻內容的復雜度,率失真性能還可以進一步提升。針對此問題,本文提出了基于復雜度分析的HEVC幀內碼率控制算法。根據梯度因子來表征編碼幀復雜度,梯度越大說明幀的復雜度越高,在分配時需要更多的比特來維持質量。首先通過圖像復雜度和比特之間的近似線性關系,為每一幀合理分配比特。再根據幀內實際分配比特與預分配比特之差自適應更新平滑窗口,使幀與幀之間的比特波動減小。最后結合基本單元層的碼率控制算法及時調節(jié)碼率。與Li算法相比,對于相同的PSNR值,所提算法平均可以節(jié)省2.3%的碼率,最大可以節(jié)省2.9%的碼率。視頻的客觀質量平均可以提高0.08dB,最大可以提高0.12dB。整體碼率波動性比Li要好,比特誤差進一步減少。2)為了有效解決HEVC中的碼率控制算法沒有考慮視頻特征保護的問題,提出了基于特征保護的HEVC碼率控制算法。通過獲取特征點掩膜,結合HEVC碼率控制算法的三層比特分配框架。根據特征點分布情況給每個LCU分配不同的權重,提高LCU的匹配效率。在不顯著降低視頻主客觀質量的前提下,盡可能提高視頻特征點的保護數量。實驗結果表明,所提算法與平臺HM15.0相比,在時間復雜度可接受范圍內,匹配率有所提高,平均提高1.27%,保護了更多的特征點,提升了算法的性能。
[Abstract]:With the increasing consumption of video services, people are also keen to pursue high-resolution video. The increase of video resolution brings great challenges to the storage and transmission of video. At present, how to make the code stream meet the bandwidth requirements is a hot topic in video coding. Rate control is the key to solve this problem. By controlling the coding quantization parameters, the output bit rate is close to the bandwidth and makes full use of the bandwidth. In this paper, a new video coding standard, HEVC, is studied, and some improved algorithms and strategies are proposed. It mainly includes two parts: 1) the rate control algorithm in HEVC frame does not consider the complexity of video content, and the rate-distortion performance can be further improved. To solve this problem, this paper proposes an intra-frame rate control algorithm for HEVC based on complexity analysis. The larger the gradient is, the higher the frame complexity is, and more bits are needed to maintain the quality in the allocation. Firstly, the image complexity and the approximate linear relationship between the bits are used to allocate the bits reasonably for each frame. Then the smoothing window is updated adaptively according to the difference between the actual allocation bits and the pre-allocated bits in the frame to reduce the bit fluctuation between frames. Finally, the rate is adjusted in time with the rate control algorithm of the basic unit layer. Compared with Li algorithm, the proposed algorithm can save an average rate of 2.3% and a maximum rate of 2.9% for the same PSNR value. The objective quality of video can be increased by 0.08dB on average, and the maximum by 0.12dB. In order to effectively solve the problem that the rate control algorithm in HEVC does not consider video feature protection, a rate control algorithm based on feature protection for HEVC is proposed. By obtaining feature point mask and combining with HEVC rate control algorithm, a three-layer bit allocation framework is proposed. According to the distribution of feature points, different weights are assigned to each LCU to improve the matching efficiency of LCU. The number of video feature points is improved as much as possible without significantly reducing the subjective and objective quality of video. The experimental results show that compared with HM15.0, the proposed algorithm improves the matching rate in the acceptable range of time complexity, increases the average value by 1.27, protects more feature points and improves the performance of the algorithm.
【學位授予單位】：寧波大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TN919.81

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