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。     

一种变码率到定码率视频转码压缩系统的实现

提出一种基于MPEG-2的变码率到定码率的压缩转码系统.采用的方法不改变源码流的GOP结构,综合I,P,B帧的性质调整比例调节因子,以尽量减小图像降质.根据解码量化因子及原始码流的复杂度调节转码量化因子,避免了计算宏块复杂度的大量运算.该系统可广泛用于视频媒体库码流向数字电视信道转播及卫星转播等应用.     

新软地带

DVDPlayer可在手机上全屏幕播放AVI格式的影片,内置DivX和Xvid解码器支持分辨率为176×208像素的视频,以及8KHz或16KHz的音频文件。用户可自定义影片播放的时间位置,实现快进快退功能。DVDPlayer可每秒播放15帧的画面,若视频码率为80~150 kbps,音频码率为20~40 kbps,采样率为16kHz,单声     

结合空时域下采样与重建的H.264/AVC压缩性能优化

为提高H.264/AVC标准在带宽资源严重受限时的压缩效率,采用空时域相结合的编码思路,提出了一种基于运动检测的自适应抽帧方法,并结合空域下采样与重建研究了一种改进的H.264/AVC压缩性能优化框架。在编码端,原视频先空域下采样以减少空间分辨率,然后根据视频运动特征,采用不同抽帧模式自适应地降低帧率,再经H.264/AVC编码,有效降低了编码码率。在解码端,解码视频则采用与抽帧模式相对应的运动估计与补偿插帧方法重建出抽取帧,再利用超分辨率重建技术将视频恢复到原空间分辨率。实验结果表明,所提方法在低码率段的视频压缩性能优于H.264/AVC标准编解码及相关文献方法。     

从MPEG压缩视频流中提取I帧的设计与实现

在基于视频内容的多媒体查询与检索系统中,经常希望用静态图像来表示视频内容,在视频点播中,有时需要视频服务器提供一种快进、快退的功能.提供了一种提取I帧的方法,并对PCR,DTS,PTS时间信息进行了讨论.     

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.     

HDTV视频解码器中码率缓冲的实现方法

对于采用ＭＰＥＧ－２编码格式的视频流,由于视频信源的非平衡特性和不同类型帧采用不同的压缩算法,导致序列中各类型图像之间的数据量存在较大差异。而经解码后显示的帧速率是恒定的,这就要求在解码端有一个缓冲器来实现输入码率与输出码率间的过渡。基于此,介绍了ＭＰＥＧ－２标准中对码率缓冲器的有关规定,阐述了高清晰度电视视频解码器对码率缓存的实际要求,提出了一种实现码率缓冲器的方法。     

从MPEG压缩视频流中提取I帧的设计与实现

在基于视频内容的多媒体查询与检索系统中 ,经常希望用静态图像来表示视频内容 ,在视频点播中 ,有时需要视频服务器提供一种快进、快退的功能。提供了一种提取I帧的方法 ,并对PCR ,DTS ,PTS时间信息进行了讨论。     

基于人工智能的音视频参考帧自适应算法

本文立足于广电网络现状,通过研究低延时CBR码率控制、自适应参考帧选取以及基于HEVC/AVS2的高效实时编码等视频编解码技术,开展基于人工智能的音视频参考帧自适应算法研究,从视频编码、传输、解码制播流程,实现了端到端视频流质量和码流的综合优化。除此之外,本文还提出具有广电特色的业务应用研究,为各单位采用音视频参考帧自适应算法提供参考。     

从MPEG压缩视频流中提取Ⅰ帖的设计与实现

在基于视频内容的多媒体查询与检索系统中,经常希望用静态图像来表示视频内容;在视频点播中,有时需要视频服务器提供一种快进,快退的功能,本文提供了一种提取1帧的方法,并对PCR、DTS、PTS时间信息进行了讨论。     

Design of frame dependency for VCR streaming videos

The structure of Group of pictures (GOP) is favorable for GOP-based random-access operations, while inside the GOP, the sequential coding dependency between frames is unfavorable for frame-based random-access or fast-scan operations. In a video streaming system, when some VCR operations such as fast-scan operations are performed, they may cause serious server load or network load due to the speed-up of transmitting frames. In this paper, we formulated the fast-scan and random-access operations of VCR functionality, and proposed a novel frame dependency to eliminate extra server load and minimize requirements of the network bandwidth when performing fast-scan and random-access operations. With the proposed structure, the server does not have to speed up the transmission rate of frames to fulfill the requested playback rate. The number of frames to be transmitted is also significantly reduced, and thus the network load can be decreased.     

GOP-Level Dynamic Thermal Management in MPEG-2 Decoding

In this paper, we present a dynamic thermal management (DTM) algorithm based on: 1) accurate estimation of the workload of frames in a group of pictures (GOP) in an MPEG-2 video stream and 2) slack borrowing across the GOP frames in order to achieve a thermally safe state of operation in microprocessors during the video decoding process. The proposed DTM algorithm employs dynamic voltage and frequency scaling (DVFS) while considering the frame-rate-dependent GOP deadline, variance of the frame decoding times within the GOP, and a maximum chip temperature constraint. If it becomes necessary to sacrifice video quality or violate the GOP deadline due to a low temperature bound, then the (intra-frame) spatial quality degradation and the (inter-frame) temporal quality degradation will be applied to the GOP. Experimental results demonstrate the competence and efficiency of the proposed online DTM algorithm.      

Error concealment with error level tracking and backward frame update

Conventional error concealment (EC) algorithms suffer from the quality degradation as the frame number increases within a group of pictures (GOP). Presented is an EC framework to improve the quality of frames in the rear of a GOP. The framework is composed of two phases: forward decoding and backward frame update. Experimental results show better performance in peak signal-to-noise ratio and subjective quality is obtained using this EC framework.     

Establishment of linkages across GOP boundaries for reverse playback on compressed video

Modern video coding standards are basically designed for forward playback only. Recently, we have developed a number of macroblock(MB)-based techniques to support reverse playback for compressed videos by exploiting the motion relationship between adjacent frames. Nevertheless, the MB-based techniques give no effect on traversing GOP boundaries reversely since no inter-frame prediction takes place between the last frame of one GOP and the first frame of its succeeded GOP. In this paper, we borrow ideas from the SP-picture concept in H.264 to establish linkages across GOP boundaries by encoding the last frame of each GOP as a primary SP-frame as well as its corresponding secondary SP-frame. During reverse playback across GOP boundaries, the secondary SP-frame is decoded by using the I-frame in its succeeded GOP as the motion-compensated frame. We believe that we are the first to consider SP-frames to build the linkage between two GOPs for reverse playback. Our scheme can also be used in any future coding standards that offer the similar coding mechanism of SP-frames. This approach can remarkably mitigate the required decoder complexity over 90% during reverse playback across GOP boundaries, but the straightforward implementation introduces serious drift errors. Therefore, as a further contribution of this paper, a novel scheme is designed to avoid the drift problem. Instead of arranging the primary SP-frame before the I-frame, the proposed scheme allocates various MBs within the GOP to be encoded as the SP-picture type. This completely new and unique arrangement for SP coding in which a primary SP MB and its corresponding secondary SP MB are no longer at the same time instant is specially designed for our MB-based techniques, and can be proved to eliminate the possible drift effect for reverse playback. With this allocation strategy, results from our experimental work show that the inherent GOP discontinuity problem can be avoided without introducing additional drift between forward and reverse playback.     

基于依存句法分析的分层语义通信系统

语义通信是一种全新的通信范式,可以从语义级别提高通信的可靠性,解决通信带宽与频谱资源受限的问题。针对语义通信中语义重要性划分这一问题,本文提出了一种基于依存句法分析的分层语义通信系统。首先,为了获取传输语句内部的依存句法关系,本文设计了一种基于图解码的依存句法分析模型,用于提取传输语句对应的依存句法树。其次,本文根据提取到的依存句法树提出了一种语义分层方法,并根据信道质量对不同层级的语义信息进行选择传输,从而保证关键语义的准确传递。此外,本文还引入了ERNIE语言模型,结合依存句法关系提高接收端的语义恢复能力。仿真结果表明：本文提出的语义分层方法可以有效提取传输语句的关键语义信息。与传统通信系统相比,本文所提系统显著提升了在低信噪比下的通信可靠性。     

Compressive Sensing Based Soft Video Broadcast Using Spatial and Temporal Sparsity

Video broadcasting over wireless network has become a very popular application. However, the conventional digital video broadcasting framework can hardly accommodate heterogeneous users with diverse channel conditions, which is called the cliff effects. To overcome this cliff effects and provide a graceful degradation to multi-receivers, in this paper, we use the nonlocal sparsity and hierarchical GOP structure to propose a novel CS based soft video broadcast scheme. CS has properties of minimizing bandwidth consumption and generating measurements with equal importance which are exactly needed by video soft broadcast. In the proposed scheme, the measurement data are generated by block-wise compressive sensing (BCS), and then the measurement data packets are sent over a highly dense constellation though OFDM channel to achieve a simple encoder. Ideally, with the GOP structure, inter frame has lower sampling rate than intra frame to achieve better compression efficiency. At the decoder side, due to equally-important packets and property of soft broadcast, each user can receive the noise-corrupted measurements matching its channel condition and reconstruct video. The hierarchical GOP structure is presented to explode the correlation and non-local sparsity among video frames during the recover process. Additionally, using non-local sparsity, group based CS reconstruction with adaptive dictionaries is proposed to improve decoding quality. The experimental results show that the proposed scheme provides better performance compared with the traditional SoftCast with up to 8 dB coding gain for some channel conditions.     

IRS辅助的NOMA无人机网络安全速率最大化算法

该文研究了智能反射面(IRS)辅助基于非正交多址接入(NOMA)技术的无人机(UAV)网络中的安全传输。为了使系统安全速率最大化,该文提出联合优化无人机位置、串行干扰消除解码顺序、IRS反射矩阵和UAV发射功率的资源优化问题。由于优化问题是一个混合整数非凸优化问题,该文提出一种基于块坐标下降的迭代算法,将原问题分解为3个子问题,采用基于惩罚、半正定松弛和连续凸逼近的方法求解子问题。仿真表明,所提算法的系统安全速率优于没有IRS辅助的NOMA方案和没有IRS辅助的正交多址方案。     

基于IRS辅助的异构网络中超可靠低时延通信波束成形算法设计

为了增强微小区内超可靠低时延通信(URLLC)业务在异构网络场景下的传输性能,该文提出一种基于智能超表面(IRS)辅助通信网络下最大化用户和速率的波束成形算法。异构网络中微小区采用短包通信技术,在保证宏小区用户通信质量的前提下,使用IRS提高微小区用户在一定解码错误概率下的短数据包传输性能,建立一个联合优化波束向量和IRS相移向量的微小区用户和速率最大化问题模型。通过交替固定优化变量的方式,将该非凸优化问题拆分为两个子问题,利用逐次凸逼近(SCA)的方法将原问题转换成凸优化问题,并利用交替优化算法对该问题进行求解。仿真结果表明,该算法通过部署IRS可以有效减弱异构场景下对于微小区用户的干扰,同时由于IRS的部署能够有效优化波束成形向量进而提高微小区用户的短包传输性能,并且IRS的通信增强效果与微小区用户的解码错误概率以及IRS反射单元的数量有直接关系。     

Joint Source/Channel Coding Based on Two‐Dimensional Optimization for Scalable H.264/AVC Video

The scalable extension of the H.264/AVC video coding standard (SVC) demonstrates superb adaptability in video communications. Joint source and channel coding (JSCC) has been shown to be very effective for such scalable video consisting of parts of different significance. In this paper, a new JSCC scheme for SVC transmission over packet loss channels is proposed which performs two‐dimensional optimization on the quality layers of each frame in a rate‐distortion (R‐D) sense as well as on the temporal hierarchical structure of frames under dependency constraints. To compute the end‐to‐end R‐D points of a frame, a novel reduced trellis algorithm is developed with a significant reduction of complexity from the existing Viterbi‐based algorithm. The R‐D points of frames are sorted under the hierarchical dependency constraints and optimal JSCC solution is obtained in terms of the best R‐D performance. Experimental results show that our scheme outperforms the existing scheme of [13] with average quality gains of 0.26 dB and 0.22 dB for progressive and non‐progressive modes respectively.