H.264/AVC码率控制技术

码率控制技术是视频标准的关键技术之一。决定视频编码器的输出码率的稳定性和图像质量的好坏。首先对码率控制技术进行介绍,然后基于视频标准H．264／AVC,对其GOP层、帧层、基本单元的比特分配及量化参数QP的设置等方面进行较为详细的分析．并在此基础上分析测试模型JM7．6的码率控制算法及其不足。     

一种新的H.264帧层码率控制算法

本文提出一种新型的基于H.264的帧层码率控制算法。综合考虑码率、视频序列空间复杂度和缓冲区状态,提出一种新型的I帧R-Q(码率-量化参数)模型。基于前一个GOP(帧组)的码率产生情况,调整I帧的时间复杂度,实现了I帧量化参数的自适应调整。根据HOD(差图像直方图)和P帧相对位置进行P帧的比特分配修正。仿真结果证明,所提算法相较于G012模型,可以有效提高重建视频的PSNR(峰值信噪比),降低PSNR波动,并大幅减少跳帧情况的发生。     

一种H.264帧层码率控制的改进算法

在H.264的现有帧层码率控制算法的基础上,提出了一种新的基于场景切换的码率控制算法。用P帧亮度分量的MAD比率和YUV三分量的均值相对变化的加权和来表示图像的复杂程度,并以此来分配目标码率、调整量化参数,并且编码时利用比特调整因子对分配的目标码率进行修正。在JM10.2平台下的测试结果表明,与JVT-G012中的算法相比,该算法在精确控制码率的同时,图像的视觉质量也得到了提高。     

H.264码率控制算法研究

带宽受限或存储容量受限的条件下,码率控制是影响H.264视频传输的重要因素。码率控制原理就是根据现有的传输条件在GOP层、Frame层和基本单元层分配目标比特数并因此改变量化参数,从而达到控制输出码流的目的。介绍了H.264所使用的两种码率控制算法：基于JVT-G012和基于ρ模型的码率控制算法;在PC平台上对两种算法的性能进行了测试与比较,并分析了它们各自的优劣。     

一种视频编解码技术码率控制算法的改进

H.264标准是最新的视频编码国际标准。与以前的视频压缩标准相比,H.264标准的编码可以实现高质量、低比特率的编码效果。但它的码率控制算法JVT-G017在帧级码率控制上存在不足,平均分配目标比特,线性预测目标平均绝对误差值(MAD),这导致了计算复杂度大和峰值信噪比低。对此,在JVT-G017算法基础上,对其画面组(GOP)层、帧层和基本单元层码率控制算法进行了优化改进,改进了分配目标比特数、初始量化参数(QP)和平均绝对误差值的计算方法。实验结果表明,与JVT-H017算法相比,改进算法可以更精确地分配目标比特和控制码率,并能获得较高的峰值信噪比(PSNR)。     

基于H.264的SSIM预测模型及其帧层应用

为使H.264帧层码率控制算法得到更好的主观视频质量,提出一种基于结构相似性因子的码率控制算法。提出结构相似性线性预测模型;通过预测模型预测当前帧的结构相似性,由结构相似性定义一个表征帧主观复杂度的结构相似性因子,根据它来分配当前帧的目标比特数。实验结果表明,该算法有效提高了重建视频帧结构相似性,得到了更好的主观视频质量。     

一种新的H.264/AVC码率控制改进算法*

针对头信息比特灵活多变、预测困难的问题,提出了一种新的基于概率选择的头信息比特预测方法。对于H.264码率控制算法中所采用的帧层比特平均分配而可能导致失衡的问题,引入一种新的图像复杂度衡量因子对比特分配进行调整。结合新的头信息量估计方法和新的比特分配调整方法,对原有的H.264码率控制算法进行了改进,实验证明能达到更好的效果。     

基于H264/AVC的帧层码率控制算法

在研究和分析了H.264/AVC经典码率控制算法的基础上,提出了一种新的帧层码率控制算法.该算法充分利用各帧的复杂度以及目标缓冲区优化比特分配,同时采用了卡尔曼滤波器估计MAD的方法.与以往码率控制算法相比,该算法能更加合理地分配各帧的目标比特数,MAD预测也更加精确,从而提高了量化参数QP预测的准确性.实验结果表明,该算法能提高码率控制的精度,并使图像总体质量有一定程度的提高.     

基于视点质量一致性的多视点视频码率控制

多视点视频是未来视频技术的重要发展方向,而码率控制是影响多视点视频传输质量的重要因素.基于多视点视频编码统计特性,提出了一种面向多视点视频编码的比特分配与码率控制算法.该比特分配算法分为三层:GGOP层、GOP层和帧层,其中13重点研究了GOP层比特分配,即视点间的比特分配策略,利用拉格朗日乘子法,提出了一种基于视点质量一致性优化的视点间比特分配模型.实验结果表明,与固定量化参数的控制策略相比,本算法能在精确控制输出码率的前提下,使得各视点视频质q更加均匀.     

一种HEVC低延时编码码率控制算法

传统码率控制方法常常引起视频编码器的率失真性能降底。为了在满足码率控制精度的同时改善编码器率失真性能,提出一种基于改进R-λ模型的帧级码率控制算法。根据帧率把待编码视频序列划分成多个控制单元,并为当前控制单元分配目标比特;根据控制单元层的可用比特数为当前GOP分配目标比特;根据GOP层的可用比特数为当前待编码帧分配目标比特,再利用改进的R-λ模型计算得到拉格朗日乘子λ进行编码。在通用测试条件下的实验结果显示,该算法具有较高的码率控制精度,同时改善了编码器的率失真性能。其平均码率相对误差为0.095%;以不开启码率控制的HM16.7作为基准,平均码率节省(BD-Rate)达到了2.6%。     

一种面向SVC的码率控制算法

H.264/AVC可伸缩性扩展视频编码系统(JSVM)提供了一种可伸缩视频编码(SVC)的解决方案,然而它本身并没有提供一种有效的码率控制算法.文中基于JSVM的分层预测结构,提出了一种全新的码率控制算法.首先在码率分配方面,考虑到分层B帧预测(或运动补偿时间域滤波(MCTF))结构,给出一种分层的码率分配方案;然后,针对不同类型和不同时间分解层各自的统计特性,分别为它们设计了不同的率失真(R-D)模型.实验结果表明,文中算法能够有效地控制码率,使得目标码率跟实际产生码率之间的偏差最大不超过2%;同时文中算法较大地提高了解码图像的质量,使得峰值信噪比(PSNR)在低码率端可提高1dB;另外,JSVM是通过不断调整量化参数(QP)使得实际产生的码率逐次逼近目标码率,较之这种尝试型的码率控制算法,文中基于模型的码率控制是在一次编码中产生最终的目标码率,从而大大降低了计算复杂度.     

基于Cauchy分布的H.264/AVC码率控制优化算法

由于通信信道带宽有限,有必要对视频编码的输出码率进行控制。通过引入能量均方误差(EMSE),进行视频序列统计分析,建立了一种简单的线性图像失真模型,并基于编码器中量化系数的概率分布特性,提出了改进的Cauchy分布码率模型,然后利用Lagrangian方法实现了率失真优化的位分配。实验结果表明,与H.264参考软件所采用的JVT-G012算法相比,该算法提高了码率控制精度和峰值信噪比,从而改善了解码图像的质量。     

SSIM-based joint-bit allocation for 3D video coding

The quality of a 3D video display depends on virtual view synthesis process which is affected by the bit allocation criterion. The performance of a bit allocation algorithm is dependent on various encoding parameters like quantization parameter, motion vector, mode selection, and so on. Rate-distortion optimization (RDO) is used to efficiently allocate bits with minimum distortion. In 3D video, rate-distortion (RD) property of synthesized view is used to assign bits between texture video and depth map. Existing literature on bit allocation methods use mean square error (MSE) as distortion metric which is not suitable for measuring perceptual quality. In this paper, we propose structural similarity (SSIM)-based joint bit allocation scheme to enhance visual quality of 3D video. Perceptual quality of a synthesized view depends on texture and depth map quality. Thus, SSIM-based RDO is performed on both texture and depth map where SSIM is used as distortion metric in mode decision and motion estimation. SSIM-based distortion model for synthesized view is determined experimentally. As SSIM cannot be related to quantization step, SSIM-MSE relation is used to convert distortion model in terms of MSE. The Lagrange multiplier method is used to solve the bit allocation problem. The proposed algorithm is implemented using 3DV-ATM as well as HEVC. RD curves show reduction in bitrate with an improvement in SSIM of synthesized view.     

融合视觉感知特性的HEVC率失真优化

目的 高效视频编码(HEVC)采用率失真优化技术选择最佳的编码参数,实现编码比特率和视频图像失真之间的平衡。失真度量通常采用均方误差和绝对误差和,这些方法并没有考虑人眼的主观感受。为了提高视频编码的主观感知质量,提出一个融合视觉感知特性的率失真优化算法,并应用于帧间率失真优化过程中。方法 首先定义了一个视觉感知因子,该因子考虑了人类视觉系统对视频图像的空域活动性区域、纹理区域、时域运动性区域和亮度的感知特性,然后以编码树单元为单位对拉格朗日乘子进行自适应调整,最后根据拉格朗日乘子与量化参数之间的关系,对量化参数做进一步的修正。结果 与HEVC参考软件相比,本文算法明显提高了率失真性能,对于相同的结构相似度(SSIM)分值,本文算法在随机访问和低延时配置下平均分别节省3.1%,4.9%的码率,最高能节省9.0%的码率。与代表性文献算法相比,对于相同的SSIM,本文算法在随机访问和低延时配置下平均分别增加了0.7%,2.2%的码率节省。结论 本文率失真优化策略能够根据图像不同的视觉特性自适应的调整率失真优化过程中的拉格朗日乘子,在保持编码质量基本不变的情况下,节省了码率,提高了HEVC的编码性能。     

Visual sensitivity guided bit allocation for video coding

A video bit allocation technique adopting a visual distortion sensitivity model for better rate-visual distortion coding control is proposed in this paper. Instead of applying complicated semantic understanding, the proposed automatic distortion sensitivity analysis process analyzes both the motion and the texture structures in the video sequences in order to achieve better bit allocation for rate-constrained video coding. The proposed technique evaluates the perceptual distortion sensitivity on a macroblock basis, and allocates fewer bits to regions permitting large perceptual distortions for rate reduction. The proposed algorithm can be incorporated into existing video coding rate control schemes to achieve same visual quality at reduced bitrate. Experiments based on H.264 JM7.6 show that this technique achieves bit-rate saving of up to 40.61%. However, the conducted subjective viewing experiments show that there is no perceptual quality degradation. EDICS-1-CPRS, 3-QUAL.     

Low-delay rate control for real-time H.264/AVC video coding

This paper presents an efficient rate control scheme for the H.264/AVC video coding in low-delay environments. In our scheme, we propose an enhancement to the buffer-status based H.264/AVC bit allocation method. The enhancement is by using a PSNR-based frame complexity estimation to improve the existing mean absolute difference based (MAD-based) complexity measure. Bit allocation to each frame is not just computed by encoder buffer status but also adjusted by a combined frame complexity measure. To prevent the buffer from undesirable overflow or underflow under small buffer size constraint in low delay environment,the computed quantization parameter (QP) for the current MB is adjusted based on actual encoding results at that point. We also propose to compare the bits produced by each mode with the average target bits per MB to dynamically modify Lagrange multiplier (/spl lambda//sub MODE/) for mode decision. The objective of QP and /spl lambda//sub MODE/ adjustment is to produce bits as close to the frame target as possible, which is especially important for low delay applications. Simulation results show that the H.264 coder, using our proposed scheme, obtains significant improvement for the mismatch ratio of target bits and actual bits in all testing cases, achieves a visual quality improvement of about 0.6 dB on the average, performs better for buffer overflow and underflow,and achieves a similar or smaller PSNR deviation.     

面向对象的H.264码率控制算法

提出了H.264码率控制改进算法。首先,基于帧间运动估计残差(mean absolutely difference,MAD)的空间和时间相关性提出了十字MAD预测模型;为了平衡缓冲的占有率,在分配帧比特时将前一帧的比特使用情况作为当前帧比特分配时的惩罚因子;最后,结合视频文字对象提取技术实现了基于文字对象的宏块比特分配以及量化步长的计算。实验结果表明,改进算法能在准确控制码率的情况下,提高输出序列的峰值信噪比。     

Effective macroblock layer rate control algorithm for H.264/AVC

Rate control plays a critical role in the video encoder. In this paper, an effective macroblock (MB) layer rate control algorithm is proposed for H.264/AVC to improve video quality and reduce the computational complexity. By thoroughly analyzing the temporal–spatial correlation and object direction, the mean absolute difference (MAD) value of current MB is a weighted combination of temporal MAD predicted by previous frame and spatial MAD predicted by current frame, and then four directional patterns are chosen adaptively for data point selection in quadratic rate-quantization (R-Q) model parameters estimation. Finally, a more accurate header bits prediction model is developed to improve the accuracy of allocated bits which can be used for quantization parameter (QP) calculation. Extensive experiment results show that compared with JVT-G012, the proposed algorithm achieves higher average peak signal to noise ratio (PSNR) up to 0.51 dB improvements and more accurate target bit rates.     

Low-complexity quantization for H.264/AVC

In this paper, an improved quantization technology with low-complexity is presented for H.264/AVC video codec. Multiplication factors of H.264/AVC quantizer are modified. Therefore, it is possible to reduce the bit width of the quantization and substitute large bit-width multiplier by some small bit-width adders without noticeable rate-distortion degradation in integrated circuits (ICs) design. Quantization error introduced by the modified multiplication factors is not only theoretically but also experimentally analyzed. Quantizer is optimized on register transfer level of IC design, and under the same cell CMOS technology, about 75.2% area and 76.3% dynamic power consumption are saved in each quantization unit on average compared with original H.264/AVC quantization. Experimental video coding results show that the Bjontegaard delta peak signal-to-noise ratio (PSNR) and Bjontegaard delta bit rate between the improved and original H.264/AVC quantization are very slight, which means that the improved quantization scheme is approximately the same as the original quantization scheme of H.264/AVC in rate-distortion performance.