Using curved angular intra-frame prediction to improve video coding efficiency

This article presents a new curved-based intra-frame prediction method for current and upcoming video coding standards. Our proposal extends conventional straight-line angular modes found on intra-prediction tools to model curved texture characteristics, enhancing the intra-frame prediction process. Our work targets the High Efficiency Video Coding (HEVC) standard for evaluation, although our curved-based method can be used by any other video coding standard. We model curved intra-frame prediction using an offset-based displacement calculation to each predicted sample. The proposal incurs a small bitstream overhead for transmitting the displacement information, which is offset by encoding efficiency gains. Experimental results demonstrate reduced residual energy; consequently, improving BD-Rate for the tested sequences. Evaluations applying eight curve displacement values show an average BD-Rate reduction of 2.69%, 2.49%, and 0.86% for All-Intra-8, All-Intra 10, and Random-Access configurations, respectively. The proposal allows further BD-Rate improvements, albeit at higher encoding complexity.     

SVM based approach for complexity control of HEVC intra coding

The High Efficiency Video Coding (HEVC) is adopted by various video applications in recent years. Because of its high computational demand, controlling the complexity of HEVC is of paramount importance to appeal to the varying requirements in many applications, including power-constrained video coding, video streaming, and cloud gaming. Most of the existing complexity control methods are only capable of considering a subset of the decision space, which leads to low coding efficiency. While the efficiency of machine learning methods such as Support Vector Machines (SVM) can be employed for higher precision decision making, the current SVM-based techniques for HEVC provide a fixed decision boundary which results in different coding complexities for different video content. Although this might be suitable for complexity reduction, it is not acceptable for complexity control. This paper proposes an adjustable classification approach for Coding Unit (CU) partitioning, which addresses the mentioned problems of complexity control. Firstly, a novel set of features for fast CU partitioning is designed using image processing techniques. Then, a flexible classification method based on SVM is proposed to model the CU partitioning problem. This approach allows adjusting the performance-complexity trade-off, even after the training phase. Using this model, and a novel adaptive thresholding technique, an algorithm is presented to deliver video encoding within the target coding complexity, while maximizing the coding efficiency. Experimental results justify the superiority of this method over the state-of-the-art methods, with target complexities ranging from 20% to 100%.     

Adaptive bit allocation scheme for rate control in high efficiency video coding with initial quantization parameter determination

One of the challenges in rate control (RC) lies in how to efficiently determine a target bit rate that will be used for the quantization parameter (Q_p) calculation process during video coding. In this paper, we investigate the issues over the existing bit allocation algorithms for the RC process in High Efficiency Video Coding (HEVC) and propose an complexity-based bit allocation scheme to improve the encoding performance. First, we model the relationship between encoding bit rate and texture complexity by a linear rate function. Second, compared with traditional complexity estimation methods, a more accurate model is proposed to measure the texture complexity considering the spatial–temporal correlations. Third, based on the proposed rate function and texture complexity measurement model, we develop an adaptive bit allocation scheme for RC in HEVC. At the same time, depending on the encoder buffer status, an adaptive Q_p clip range determination algorithm is also developed to achieve the encoding quality smoothness while keeping the bit rate fluctuation at an acceptable level. Then, we exploit to determine the initial Q_p efficiently and adaptively according to video contents. Experimental results demonstrate that the proposed RC algorithm can achieve better rate-distortion (R–D) and rate-control performance than that of the state-of-the-art RC scheme implemented in the HEVC reference software HM11.0.     

基于SSIM的HEVC帧内编码率失真优化

率失真优化(RDO)是视频编码压缩中的关键技术之 一。传统的率失真优 化技术使用误差平方和(SSE)或绝对差和(SAD)度量失真, 不能获得较好的视觉感知质量。本文针对新一代视频编码标准高效视频编码(H EVC)帧内编码RDO,提出了一种基于结构相似度(SSIM)度量失真的 RDO方法。首先,根据HEVC编码树形单元(CTU)结构设计了基于SSIM的失真计算方法; 然后,提出了一种基于量化器推导的码率-量化步长(R-Δ)模型和一种基于统计分析的失 真 -量化参数(DSSIM-QP)模型,用于求取拉格朗日乘数;最终,使用多QP优化方法求 取模 型参数。实验表明,相对于HEVC 传统的RDO,针对全I帧(即所有帧都为帧内编码)固定QP编码和多QP优化编 码,在相同的SSIM条 件下,码率分别平均降低8.4%和13.9%左右,同时编码复杂度分别平均增加约3%和2%。     

基于零块分析的高效视频编码通信

为了实现高清、超高清视频实时编码通信传输, 针对高效视频编码(HEVC)帧间编码计算复杂度过高的问题,根据图像的文理复杂度和 编码单元的零块统计特征,提出一种新的HEVC快速帧间模式判决算法。根据Merge模式下 整单元一分为四的4个子编码单元纹 理相似度确定是否提前终止编码单元(CU)划分,同时利用帧间2N×2N预测模式下零系数与非零系数分布的区域统计特征,选择符合零块分 布特征的最佳预测单元(PU)模式。实验结果表明,在低延迟B(LDB,low-delay B)和随机访 问(RA,random access)配置条件下,提出的算法在保持编码 性能基本不变的情况下,HEVC帧间预测编码时间分别平均减少了60.2%与59.4%。     

Rough mode cost–based fast intra coding for high-efficiency video coding

The quadtree-based coding unit (CU) and transform unit (TU) structure, as well as various prediction units (PUs) of HEVC, considerably increase encoding complexity in intra coding and inter coding. This paper proposes a rough mode cost (RMC)-based algorithm for accelerating CU/TU depth decisions and PU mode decisions in HEVC intra coding. For CU depth decisions, RMC values are used for the fast determination of CU partition. In the case of PU mode decisions, modes with higher RMCs are removed from the candidate list to reduce the number of test modes. For TU depth decisions, the TU partition of the mode with the least RMC is used to determine the TU partitions of remaining modes. The proposed TU partitioning method demonstrates superior performance to the default method in reference software. The proposed algorithm can reduce encoding time by approximately 51% on average, with a 0.69% increase in the Bjøntegaard-Delta (BD) rate.     

一种无帧内失真漂移的HEVC视频自适应隐写算法

随着数字视频的普及,HEVC(high efficiency video coding)视频隐写受到了越来越多的关注。残差系数域隐写具有高安全性和低码率增长的特点,然而,视频编码过程中重构的系数不满足块间相互独立的性质,导致修改视频残差系数往往会带来较为严重的失真漂移。本文提出了一种无帧内失真漂移的HEVC视频自适应隐写算法。首先,根据帧内预测方向和多系数修改的方法选择合适的载体,进而避免修改系数引起的失真漂移。然后,设计一种包含块内失真和修改载体后的系数分布的失真函数,指导校验网格编码(syndrome trellis codes, STC)对嵌入失真小的载体进行修改。最后,根据最小化失真代价将消息嵌入到满足特定条件的4×4亮度块的量化正弦变换(quantized discrete sinc transform, QDST)系数中。实验结果表明,所提出的视频隐写算法能够有效地避免帧内失真漂移,在获得良好的视觉感知质量的同时,能保证隐写算法的安全性。     

Accelerating QTMT-based CU partition and intra mode decision for versatile video coding

The H.266/VVC achieves about 50% bitrate saving compared to its predecessor H.265/HEVC at the expense of exponentially increased computational complexity. The most efficient but complex technique for H.266/VVC intra frame coding is the QuadTree with a nested Multi-type Tree encoding structure (QTMT), which usually requires traversing the Rate-Distortion (R-D) cost of each partition and each mode for the best option. To alleviate such computational burden while preserving the coding efficiency as much as possible, this paper develops a multi-feature guided Fast CU Partition (FCP) and Laplacian guided Fast Mode Selection (FMS) to accelerate the intra QTMT decision together. For FCP, we regard the CU partition as a classification problem and adopt the Support Vector Machine (SVM) for its low-complexity implementation; after evaluating the contribution of a set of features, three representative features of video textures are selected and used to train the SVM model. Additionally, an advanced technique is applied by adopting a soft decision in SVM for a more flexible trade-off between the complexity and R-D performance. For FMS, we utilize the Laplace operator to determine the most probable directions of the current CU and skip half of the candidate modes for runtime saving. Experimental results demonstrate that the proposed FCP reduces the encoding time of H.266/VVC by 51.03% with 1.65% Bjøntegaard Delta Bit-Rate (BDBR) increase; the proposed FMS reduces the encoding time by 12.68% with 0.09% BDBR loss. Their direct combination and advanced combination finally lead to 54.84% encoding time reduction with 1.74% BDBR increase and 40.39% encoding time reduction with 1.33% BDBR increase, respectively, outperforming state-of-the-art approaches significantly.     

Perceptual feature guided rate distortion optimization for high efficiency video coding

With the advances in understanding perceptual properties of the human visual system, perceptual video coding, which aims to incorporate human perceptual mechanisms into video coding for maximizing the perceptual coding efficiency, becomes an essential research topic. Since the newest video coding standard—high efficiency video coding (HEVC) does not fully consider the perceptual characteristic of the input video, a perceptual feature guided rate distortion optimization (RDO) method is presented to improve its perceptual coding performance in this paper. In the proposed method, for each coding tree unit, the spatial perceptual feature (i.e., gradient magnitude ratio) and the temporal perceptual feature (i.e., gradient magnitude similarity deviation ratio) are extracted by considering the spatial and temporal perceptual correlations. These perceptual features are then utilized to guide the RDO process by perceptually adjusting the corresponding Lagrangian multiplier. By incorporating the proposed method into the HEVC, extensive simulation results have demonstrated that the proposed approach can significantly improve the perceptual coding performance and obtain better visual quality of the reconstructed video, compared with the original RDO in HEVC.     

Wyner-Ziv视频编码中无反馈速率控制算法研究

为了避免在分布式视频编码系统中使用反馈信道,提出了一种基于Wyner-Ziv编码的无反馈速率控制算法。首先,利用目标码率和目标帧率进行GOP层码率分配;然后,根据原始图像的帧间相关性动态选择量化因子和量化矩阵来分配每个GOP内关键帧和Wyner-Ziv帧的比特数;接下来,利用系数带级的相关性计算相关噪声模型参数,并选择对应的LDPC校验矩阵,提出Wyner-Ziv帧的无反馈比特面速率控制算法。实验结果表明,在给定目标码率下,所提算法的编码码率误差小于0.57%,且与现有无反馈速率控制算法相比,解码恢复图像的PSNR(峰值信噪比)可以提高1dB。另外,该算法基本没有增加编码端复杂度,可用于实际分布式视频通信系统。     

Gamma rate theory for causal rate control in source coding and video coding

The rate distortion function in information theory provides performance bounds for lossy source coding. However, it is not clear how to causally encode a Gaussian sequence under rate constraints while achieving R–D optimality. This problem has significant implications in the design of rate control for video communication. To address this problem, we take distortion fluctuation into account and develop a new theory, called gamma rate theory, to quantify the trade-off between rate and distortion fluctuation. The gamma rate theory implies that, to evaluate the performance of causal rate controls in source coding, the traditional R–D metric needs to be replaced by a new GRD metric. The gamma rate theory identifies the trade-off between quality fluctuation and bandwidth, which is not known previously. To validate the gamma rate theory, we design a rate control algorithm for video coding; our experimental results demonstrate the utility of the gamma rate theory in video coding.     

FITD: Fast Intra Transcoding from H.264/AVC to high efficiency video coding based on DCT coefficients and prediction modes

In the literatures, the designs of H.264 to High Efficiency Video Coding (HEVC) transcoders mostly focus on inter transcoding. In this paper, a fast intra transcoding system from H.264 to HEVC based on discrete cosine transform (DCT) coefficients and intra prediction modes, called FITD, is proposed by using the intra information retrieved from an H.264 decoder for transcoding. To design effective transcoding strategies, FITD not only refers block size of intra prediction and intra prediction modes, but also effectively uses the DCT coefficients to help a transcoder to predict the complexity of the blocks. We successfully use DCT coefficients as well as intra prediction information embedded in H.264 bitstreams to predict the coding depth map for depth limitation and early termination to simplify HEVC re-encoding process. After a HEVC encoder gets the prediction of a certain CU size from depth map, if it reaches the predicted depth, the HEVC encoder will stop the next CU branch. As a result, the numbers of CU branches and predictions in HEVC re-encoder will be substantially reduced to achieve fast and precise intra transcoding. The experimental results show that the FITD is 1.7–2.5 times faster than the original HEVC in encoding intra frames, while the bitrate is only increased to 3% or less and the PSNR degradation is also controlled within 0.1 dB. Compared to the previous H.264 to HEVC transcoding approaches, FITD clearly maintains the better trade-off between re-encoding speed and video quality.     

Spatial quality index based rate perceptual-distortion optimization for video coding

Spatial Quality Index (SQI) is a recently proposed video quality assessment metric that can predict video quality much close to subjective judgments. Since current video coding still has much redundancy in the sense of visual perception, in this paper, we incorporate SQI into video coding to further improve compression ratio without visual quality loss. Firstly, contributions of different human visual system (HVS) properties used in SQI are analyzed. Then two most important HVS properties, i.e. contrast masking effect (CME) and motion masking effect (MME), are extracted to measure perceptual-distortion D_p in video coding. Finally, based on D_p, a rate perceptual-distortion optimization (RpDO) algorithm is presented by adopting a suitable Lagrange multiplier from previous study. Experimental results show that, RpDO can averagely achieve 14% bitrate reduction when compared to HM14.0 under the same visual quality. At the same time, there is no significant change in the encoding time.     

A two-pass rate control algorithm for H.264/AVC high definition video coding

In this paper, we propose a novel two-pass rate control algorithm to achieve constant quality for H.264/AVC high definition video coding. With the first-pass collected rate and distortion information and the built model of scene complexity, the encoder can determine the expected distortion which could be achieved in the second-pass encoding under the target bit rate. According to the built linear distortion-quantizer (D-Q) model, before encoding one frame, the quantization parameter can be solved to realize constant quality encoding. After encoding one frame, the model parameters will be updated with linear regression method to ensure the prediction accuracy of the quantization parameter of next encoded frame with the same coding type. In order to obtain the expected distortion of each frame under the target bit rate, a GOP-level bit allocation scheme is also designed to adjust the target bit rate of each GOP based on the scene complexity of the GOP in the second-pass encoding. In addition, the effect of scene change on the updating of D-Q model is considered. The model will be re-initialized at the scene change to minimize modeling error. The experimental results show that compared with the latest two-pass rate control algorithm, our proposed algorithm can significantly improve the bit control accuracy at comparable coding performance in terms of constant quality and average PSNR. On average, the improvement of bit control accuracy achieved about 90%.     

Adaptive rate control algorithm for low power video coding systems

With the recent development of third-generation communication technologies, low power video coding system (such as PDA, Handphone or system on chip) has found wide applications such as live video using a PDA and sharing it among friends, etc. However, video coding in a low power system has two major hurdles to overcome: (1) In a low power system, video coding needs to meet the rigorous constraints of the available memory and computational capacity; (2) In a low power system, the computational power allocated to video coding may vary drastically (in bursts). In this paper, a new adaptive rate control algorithm is proposed for low power video coding system. This adaptive rate control scheme takes into account the time constraint of a low power system, and its bit allocation depends not only on the available data bits, but more importantly, on the available coding time. Experimental results show that, compared to the existing rate control scheme, the new algorithm can always achieve the maximum frame rate, maximize the utilization of the available bandwidth and computing power, increase the average PSNR, and improve the subjective perceptual quality of the reconstructed video.     

Mode dependent down-sampling and interpolation scheme for high efficiency video coding

In this paper, a mode dependent down-sampling and interpolation scheme is proposed to improve the coding efficiency of the intra prediction module. In the proposed method, we elaborately design the down-sampling structures and interpolation schemes for each directional intra prediction mode by minimizing the spatial prediction distance. The sampled pixels are predicted with a traditional directional intra prediction scheme, and the non-sampled pixels are predicted from the interpolation of their neighboring reconstructed sampling pixels. Both the residuals of the sampled and non-sampled pixels are encoded at last. Experimental results show that the proposed method achieves an average 7.52% bitrate reduction relative to KTA reference software. Since the down-sampling structure and interpolation method is only related to the intra mode, there is no additional overhead at the encoder.     

一种场景切换下的HEVC码率控制算法

针对HEVC(High Efficiency Video Coding)编码器对图像组(Group of Picture,GOP)层采用平均分配的方式,在场景切换背景下,容易导致场景切换帧以及后续视频图像质量严重下降的问题,本文提出一种基于场景切换的码率控制算法:根据场景的复杂度,重新分配GOP层目标比特,并且当检测到场景切换时,对模型参数,当前帧以及参考帧等做出适当调整.实验结果表明:相比HEVC自带的码率控制算法,该策略能有效降低场景切换带来的负面影响,使序列的平均峰值信噪比(PSNR)最高提升1.4 dB,并保持精确的输出码率.     

低码率应用中的一种视频码率控制方法

针对低码率视频应用,该文根据信源的线性模型,在满足码率约束的条件下,提出一种使宏块量化参数集中的优化策略。通过该方法,可以使宏块失真度分布更加集中,图像质量更加均匀,更符合人眼视觉特性;同时减少了编码码流中用于表征宏块间量化参数变化的句法比特数。仿真表明,在低码率及甚低码率的视频应用中,该方法能改善主客观视觉质量。     

Efficient rate control scheme for low bit rate H.264/AVC video coding

This article presents an efficient rate control scheme for H.264/AVC video coding in low bit rate environment. In the proposed scheme, an improved rate-distortion (RD) model by both analytical and empirical approaches is developed. It involves an enhanced mean absolute difference estimating method and a more rate-robust distortion model. Based on this RD model, an efficient macroblock-layer rate control scheme for H.264/AVC video coding is proposed. Experimental results show that this model encodes video sequences with higher peak signal-to-noise ratio gains and generates bit stream closer to the target rate.