基于视频并行编码的码率控制算法研究

基于并行编码的特点,现有的基于串行编码的码率控制算法有其局限性,不能直接应用于并行编码。本文提出一种新的码率控制算法,在编码前将原始帧作为参考帧计算出各帧的SAD,然后利用已计算的SAD进行帧级比特分配和动态预测并行编码帧的比特,实现了并行编码的码率控制。通过测试基于串行编码的码率控制和本文提出的码率控制方案下PSNR和VBV情况,说明本文所提算法的可行性。     

一种基于分层B帧架构的高效比特分配算法

随着分层B帧码率控制技术在SVC(可伸缩视频编码)中的广泛应用,视频编码的质量得到了很大提高,然而传统的H.264码率控制技术并未将B帧的比特分配考虑在内。提出一种基于分层B帧架构自适应调节B帧比特分配的码率控制算法,该算法研究了基于同一个图像组(GoP)中各时域层权重因子的自适应调节,为各时域层分配不同的目标比特;同时基于同一个时域层中各帧复杂度的不同,为各帧分配不同的目标比特。实验结果表明,与目前流行的分层B帧码率控制算法相比,该算法在比特控制误差并未降低的情况下,客观质量PSNR可提高0.1～0.4 dB。     

基于H.264标准的码率控制改进算法

本文利用视频编码的线性码率控制(RC)算法(Rho-Domain算法)对原有的H.264标准中的RC算法进行了改进.首先,对于视频序列中的Ⅰ帧图像,使用Rho-domain算法进行码率控制.由于该算法基于本帧的图像内容,所以能够及时地对Ⅰ帧进行精确的码率调整;其次,使用了新的关于P帧的比特分配原则,根据GOP中的位置来分配P帧的比特数;最后,对模型的估算方法作了改进,使模型参数的计算更为精确.实验结果表明,改进后的算法能更加有效准确的控制编码序列的码率.     

基于梯度的HEVC自适应码率控制算法研究

针对新一代视频编码标准HEVC中的码率控制问题,提出了一种基于梯度的自适应码率控制算法.算法的主要特点是自适应获取每个LCU的梯度来表示其复杂度,根据复杂度分配LCU层目标比特.同时,在分配帧层目标比特时利用缓冲区的状态信息,以使编码器输出的实际码率更符合给定的目标码率,并使缓冲区滞留的数据尽量少,即传输时延尽量小.实验结果表明,该算法与标准的HEVC码率控制提案K0103相比,缓冲区滞留数据量平均减少约39.31％,峰值信噪比平均提高约0.54 dB,同时实际码率与目标码率之间的码率偏差平均降低约0.39％.     

面向统计编码的联合比特分配算法

在统计编码系统中,需根据图像复杂度对各路节目进行联合比特分配,比特分配的准确性直接影响了图像质量.因此对图像复杂度的准确评估是统计编码的难点.鉴于传统的基于预测的算法对复杂度评估存在预测误差,提出了将原始帧作为参考帧,通过并行整像素运动估计计算各编码帧的SAD作为统计所需的复杂度信息,提高了图像复杂度评估的准确性,进而提高统计编码性能.通过测试CBR模式下和提出的统计算法下的视频码率以及图像质量来说明所提出算法的可行性.     

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。     

基于神经网络的量化参数预测研究

在视频有损压缩编码中,量化是为达到压缩视频的目的,将原信号值映射到较小取值范围的过程。一个合适的量化参数(QP)可以在增加压缩效率的同时平衡视频质量和编码复杂度。现有的码率控制算法对运动剧烈及存在场景切换的连续帧控制不精确,视频PSNR值波动大。本文提出一种基于神经网络的视频量化参数选择,利用已编码帧信息对当前帧的量化参数计算进行调整。神经网络模型选取当前帧的目标比特、当前帧的MAD和前一帧编码的QP和实际比特数作为输入,输出值经过反归一化及取整处理对视频进行量化。实验表明,编码时使用该方法进行与H.264/AVC的标准参考软件JM14.2相比,在保证码率精确度和平均PSNR值基本不变的情况下,减小了PSNR的波动。     

基于神经网络的视频编码量化参数选择算法

提出了一种基于神经网络的视频量化参数选择,利用已编码帧信息对当前帧的量化参数计算进行调整.神经网络模型选取当前帧的目标比特、当前帧的MAD和前一帧编码的QP和实际比特数作为输入,输出值经过反归一化及取整处理对视频进行量化.实验在H.264/AVC的标准参考软件JM14.2中实现,编码时使用该方法在保证码率精确度和平均PSNR值基本不变的情况下,减小了PSNR的波动.     

基于线性模型的分级B帧比特分配改进算法

针对分级B帧编码结构,提出了一种基于比特分配线性模型的码率控制算法.通过实验发现不同时间级B帧平均比特数与P帧比特数呈良好的线性关系,利用此线性关系对B帧进行比特分配可以充分利用不同时间级B帧的特性,提高分级B帧结构码率控制的性能.实验结果表明,该算法与JVT-W042相比,对于大部分内容特性序列,平均△SNR提高0.15 dB以上.     

一种低复杂度的HEVC码率控制算法

针对HEVC视频编码中帧层比特分配和率失真模型参数自适应更新,提出了一种改进的码率控制算法.该算法引入牛顿法来自适应更新率失真模型的参数;同时提出一种帧层复杂度度量方法,利用图像自身的内容特性来调整帧层比特分配;最后在编码过程中选择合适的量化参数.实验结果表明:与参考算法比较,该算法能大大降低计算复杂度,同时保持良好的码率控制性能,对含有场景突变的视频改进效果尤为明显.     

A new rate control scheme for H.263 video transmission

In some image/video applications, the variable bit rate image/video bitstream will be transmitted over a constant bit rate transmission channel, in which a channel buffer is employed. In this study, a new rate control scheme for H.263 video transmission is proposed. Three proposed techniques include: preprocessing the INTRA coded macroblock (MB) incorporated the just-noticeable-distortion (JND) concept, constructing a bit estimation model in the frequency domain (instead of the bit estimation model in the spatial domain employed in Test Model Near-term version 11 (TMN11)), and adjusting quantization parameter (QP) for each MB by a Lagrangian optimization strategy.In the proposed approach, the target number of bits for a video frame is first obtained by using a simple rate control procedure for the frame layer. The proposed JND preprocessing is applied on all the INTRA coded MBs so that the number of coded bits for a scene changed frame will decrease, without any perceptual loss. Within the MB layer, instead of the bit estimation model in the spatial domain employed in TMN11, a bit estimation model in the frequency domain, directly depending on discrete cosine transform coefficients, is proposed. Then the Lagrange multiplier is used to determine the optimal QP for each MB. The resulting QP and number of coded bits of the current MB are fed backward to update the parameters of the bit estimation model.Based on the simulation results obtained in this study, the proposed approach can meet the target bit rate more accurately, keep a lower channel buffer fullness (delay), and have a larger average frame rate than TMN11, whereas the peak signal-to-noise ratio value and the processing time of the proposed approach are “approximately” as good as that of TMN11.     

Rate control of MPEG video for consistent picture quality

We propose a rate control scheme using a rate-distortion (R-D) estimation model, which produces a consistent picture quality between consecutive frames. Our R-D estimation method offers a closed-form mathematical model that enables us to predict the bits and the distortion generated from a frame encoded at a given quantization parameter (QP) and vice versa. Its most attractive feature is its low computational complexity. Furthermore, it is accurate enough to be applied to practical video coding. In our simulation, the estimation errors for rate and distortion are less than 2.5% and 1.5%, respectively. Therefore, the proposed rate control scheme is appropriate for applications requiring low delay, low complexity, and the ability to control output bit-rate and quality accurately. Our scheme ensures that the video buffers do not underflow or overflow by satisfying the buffer constraint, and it also prevents quality difference between consecutive frames from exceeding a certain demanded level by adopting a distortion constraint. In addition, a consistent picture quality is maintained within a frame, and error propagation, caused by quality degradation of anchor frames, is reduced by differentiating the control procedure for anchor frames from that for nonanchor frames. Simulation results show that our control scheme achieves 0.52-1.84 dB peak signal-to-noise ratio (PSNR) gain over MPEG-2 Test Model 5 (TM5) rate control and maintains very consistent quality within a frame as well as between frames.     

Introducing skip mode in distributed video coding

Although it was proven in the 1970s already by Wyner and Ziv and Slepian and Wolf that, under certain conditions, the same rate–distortion boundaries exist for distributed video coding (DVC) systems as for traditional predicting systems, until now no practical DVC system has been developed that even comes close to the performance of state-of-the-art video codecs such as H.264/AVC in terms of rate–distortion. Some important factors for this are the lower accuracy of the motion estimation performed at the decoder, the inaccurate modeling of the correlation between the side information and the original frame, and the absence in most state-of-the-art DVC systems of anything conceptually similar to the notion of skipped macroblocks in predictive coding systems.This paper proposes an extension of a state-of-the-art transform domain residual DVC system with an implementation of skip mode. The skip mode has an impact at two different places: in the turbo decoder, more specifically the soft input, soft output (SISO) convolutional decoder, and in the puncturing of the parity bits. Results show average bitrate gains up to 39% (depending on the sequence) achieved by combining both approaches.Furthermore, a hybrid video codec is presented where the motion estimation task is shifted back to the encoder. This results in a drastic increase in encoder complexity, but also in a drastic performance gain in terms of rate–distortion, with average bitrate savings up to 60% relative to the distributed video codec. In the hybrid video codec, smaller but still important average bitrate gains are achieved by implementing skip mode: up to 24%.     

Error-resilient coding of H.264 based on periodic macroblock

For the compressed video, since an inter-frame depends on the previously encoded frame, the error in one inter-frame may propagate to the following inter-frames. In this paper, we present a new error-resilient coding scheme to alleviate the effect of error propagation for the new coding standard H.264. In this new coding standard, multiple reference frame is adopted to improve the coding efficiency. By making use of the reference frame buffer in the encoder, we can reference some macroblocks in every n/sup th/ inter-frame to the frame that is n frames interval away, and these macroblocks are named as periodic macroblocks. The periodic macroblock can efficiently alleviate the error propagation between two frames that contain periodic macroblocks. We prove it in theory that encoding selected periodic macroblocks will reduce the loss probability of pixel. The selection of periodic macroblock is based on the distortion expectation of each macroblock in every n/sup th/ frame. The number of periodic macroblocks in every n/sup th/ frame can be adjusted according to the available transmission bandwidth, as the periodic macroblock will consume little more bits. The simulation results prove that the periodic macroblocks can obviously improve the quality of video at different macroblock loss rates. When the macroblock lost rate is 15% in every frame, the PSNR of video sequence can be improved about 3dB with 5% bitrate increase.     

Nonlinear fuzzy rule-based approach for estimating video trafficrate

The authors investigate a fuzzy logic-based video rate control technique which aims to regulate compressed video to a constant transmission rate, without incurring objectionable quality degradation. Conventional fuzzy rule-based control (FRC) does not adequately control the output video quality. Video information is therefore added into the FRC design by incorporating feed-forward scaling factors, derived from scene change features. The performance of this coder has been compared with other approaches measuring buffer occupancy, the number of coded bits per frame and peak signal-to-noise ratio     

Reduced decoder complexity and latency in pixel-domain Wyner–Ziv video coders

In some video coding applications, it is desirable to reduce the complexity of the video encoder at the expense of a more complex decoder. Wyner–Ziv (WZ) video coding is a new paradigm that aims to achieve this. To allocate a proper number of bits to each frame, most WZ video coding algorithms use a feedback channel, which allows the decoder to request additional bits when needed. However, due to these multiple bit requests, the complexity and the latency of WZ video decoders increase massively. To overcome these problems, in this paper we propose a rate allocation (RA) algorithm for pixel-domain WZ video coders. This algorithm estimates at the encoder the number of bits needed for the decoding of every frame while still keeping the encoder complexity low. Experimental results show that, by using our RA algorithm, the number of bit requests over the feedback channel—and hence, the decoder complexity and the latency—are significantly reduced. Meanwhile, a very near-to-optimal rate-distortion performance is maintained. This work has been partially supported by the Spanish Ministry of Education and Science and the European Commission (FEDER) under grant TEC2005-07751-C02-01. A. Pižurica is a postdoctoral research fellow of FWO, Flanders.     

Rate control for consistent visual quality of H.264/AVC encoding

In this paper, a novel rate control scheme with sliding window basic unit is proposed to achieve consistent or smooth visual quality for H.264/AVC based video streaming. A sliding window consists of a group of successive frames and moves forward by one frame each time. To make the sliding window scheme possible for real-time video streaming, the initial encoder delay inherently in a video streaming system is utilized to generate all the bits of a window in advance, so that these bits for transmission are ready before their due time. The use of initial encoder delay does not introduce any additional delay in video streaming but benefits visual quality as compared to traditional one-pass rate control algorithms of H.264/AVC. Then, a Sliding Window Buffer Checking (SWBC) algorithm is proposed for buffer control at sliding window level and it accords with traditional buffer measurement of H.264/AVC. Extensive experimental results exhibit that higher coding performance, consistent visual quality and compliant buffer constraint can be achieved by the proposed algorithm.     

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.