H.264可伸缩视频编码层间码率控制算法

为H.264/AVC标准的可伸缩编码(SVC)扩展提出了一种自适应的层间码率控制算法。该算法提出了一个选择模型,通过当前层的前一帧或者前一层的当前帧来预测Inter帧所需比特数。首先,将码率—复杂度—量化因子(R-C-Q)模型引入可伸缩的视频编码;接着,使用一个已有的比例—积分—微分(PID)缓冲区控制器来根据缓冲区状态提供当前Inter帧的比特数估计;然后,为了在视频画面发生急剧变化时获得更为精确的估计,利用前一层中的当前帧所用实际比特数来进一步进行当前Inter帧比特数估计;最后,使用选择模型决定最终的预测比特数,并通过R-C-Q模型计算出量化因子(QP)。实验结果表明,相对于推荐的JVT-043码率控制算法,所提出的算法可以在SVC的每层获得更加精确的实际输出比特率,保持缓冲区充盈度的稳定,同时减少跳帧和质量波动,提高整体编码质量。     

Fast video transcoding from H.263 to H.264/MPEG-4 AVC

In the past 10 years detailed works on different video transcoders have been published. However, the new ITU-T Recommendation H.264—also adapted as ISO/IEC MPEG-4 Part 10 (AVC)—provides many new encoding options for the prediction processes that lead to difficulties for low complexity transcoding. In this work we present very fast transcoding techniques to convert H.263 bitstreams into H.264/AVC bitstreams. We will give reasoning, why the proposed pixel domain approach is advantageous in this scenario instead of using a DCT domain transcoder. Our approach results in less than 9% higher data rate at equivalent PSNR quality compared to a full-search approach. But this rate loss allows the reduction of the search complexity by a factor of over 200 for inter frames and still a reduction of over 70% for intra frames. A comparison to a fast search algorithm is given. We also provide simulation results that our algorithm works for transcoding MPEG-2 to H.264/AVC in the aimed scenario.

重用运动矢量和预测残差的MPEG-2/H.264空间分辨率转码

本文提出一种新的MPEG-2到H.264的视频转码算法.它通过充分利用MPEG-2解码过程中得到的运动矢量和宏块编码残差等信息,可显著减少H.264编码过程中宏码编码模式确定和运动估计过程的计算复杂度,并得到最终的H.264视频流.几种典型视频测试序列的仿真实验结果表明,本算法对视频质量的损失较小,有稳定的率失真性能,有利于实时转码的实现.     

MPEG-2到H.264/AVC转码中的快速模式选择算法

为了降低MPEG-2到H.264/AVC的转码复杂度,针对转码过程中H.264/AVC编码的多模式预测,提出一个有效的快速模式选择算法.算法用MPEG-2中已有的运动矢量的差异来衡量宏块的运动情况,对运动矢量进行聚类,进而用聚类结果来选择预测模式.实验结果表明,算法可以在视频质量损失很小的情况下大幅度降低转码中再编码的复杂度.     

一种H.264/AVC over MPEG-2流的解决方案

对如何将H．264／AVC视频流经MPEG-2的系统传输层传输提出了一种解决方案。要点是：先把H．264／AVC视频作为MPEG-2系统层传输的基本流，然后扩展MPEG-2标准中的传输流系统目标解码器（T-STD），使之可以将H．264／AVC编码视频作为MPEG．2传输流（TS）在Internet上传输和解码。被解码的基本流通常来自于一个“容器”文件（如AVI或者TS），在客户端从服务器端的这个容器中取出H．264／AVC基本流后便可实时解码、显示。仿真实验表明，该方案能够获得较好的流视频效果，在带宽受限的情况下信噪比低于40dB的帧数少于5％，可用于网络流视频或移动视频中。     

Simple intra prediction algorithms for heterogeneous MPEG-2/H.264 video transcoders

Recent developments have given birth to H.264/AVC: a video coding standard offering better bandwidth to video quality ratios than MPEG-2. It is expected that the H.264/AVC will take over the digital video market, replacing the use of MPEG-2 in most digital video applications. The complete migration to the new video-coding algorithm will take several years given the wide scale use of MPEG-2 in the market place today. This creates an important need for MPEG-2/H264 transcoding technologies. However, given the significant differences between both encoding algorithms, the transcoding process of such systems is much more complex to other heterogeneous video transcoding processes. In this work, we start by analyzing the methods defined in the H.264 video coding standard for the intra prediction: a central element of every H.264 encoder. We then introduce and evaluate six fast intra mode decision algorithms which should enable the development of MPEG-2 to H.264 transcoders. Having evaluated all the proposed methods, we have come out with a high-efficient method, namely DC-ABS pixel. Our results show that our algorithm considerable reduces the complexity involved in the intra prediction with respect the mode decision algorithms used in H.264 JM reference software, while exhibiting a slight degradation on the RD function.. Finally, we analyze a comparative study with two of the most prominent fast intra prediction methods presented in the literature. The results show that the proposed DC-ABS pixel method achieves the best results for video transcoding applications.

Motion mapping and mode decision for MPEG-2 to H.264/AVC transcoding

This paper describes novel transcoding techniques aimed for low-complexity MPEG-2 to H.264/AVC transcoding. An important application for this type of conversion is efficient storage of broadcast video in consumer devices. The architecture for such a system is presented, which includes novel motion mapping and mode decision algorithms. For the motion mapping, two algorithms are presented. Both efficiently map incoming MPEG-2 motion vectors to outgoing H.264/AVC motion vectors regardless of the block sizes that the motion vectors correspond to. In addition, the algorithm maps motion vectors to different reference pictures, which is useful for picture type conversion and prediction from multiple reference pictures. We also propose an efficient rate-distortion optimised macroblock coding mode decision algorithm, which first evaluates candidate modes based on a simple cost function so that a reduced set of candidate modes is formed, then based on this reduced set, we evaluate the more complex Lagrangian cost calculation to determine the coding mode. Extensive simulation results show that our proposed transcoder incorporating the proposed algorithms achieves very good rate-distortion performance with low complexity. Compared with the cascaded decoder-encoder solution, the coding efficiency is maintained while the complexity is significantly reduced.

Integrating semantic analysis and scalable video coding for efficient content-based adaptation

Scalable video coding has become a key technology to deploy systems where the adaptation of content to diverse constrained usage environments (such as PDAs, mobile phones and networks) is carried out in a simple and efficient way. Content-based adaptation and summarization are fields that aim for providing improved adaptation to the user, trying to optimize the semantic coverage in the adapted/summarized version. This paper proposes the integration of content analysis with scalable video adaptation paradigm. They must be fitted in such a way that the efficiency of scalable adaptation is not damaged. An integrated framework is proposed for semantic video adaptation, as well as an adaptive skimming scheme that can use the results of semantic analysis. They are described using the MPEG-21 DIA tools to provide the adaptation in a standard framework. Particularly, the case of activity analysis is described to illustrate the integration of semantic analysis in the framework, and its use for online content summarization and adaptation. Overall efficiency is achieved by means of computing activity using compressed domain analysis with several metrics evaluated as measures of activity. Work supported by the Ministerio de Ciencia y Tecnología of the Spanish Government under project TIN2004-07860 (MEDUSA) and by the Comunidad de Madrid under project S-0505-TIC-0223 (PROMULTIDIS).     

DAg-stream: Distributed video adaptation for overlay streaming to heterogeneous devices

Combining the advantages of Peer-to-Peer (P2P) content distribution concept and metadata driven adaptation of videos in compressed domain, in this paper, we propose a simple but scalable design of distributed adaptation and overlay streaming using MPEG-21 gBSD, called DAg-stream. The objective is not only to shift the bandwidth burden to end participating peers, but also to move the computation load for adapting video contents away from dedicated media-streaming/adaptation servers. It is an initiative to merge the adaptation operations and the P2P streaming basics to support the expansion of context-aware mobile P2P systems. DAg-stream organizes mobile and heterogeneous peers into overlays. For each video, a separate overlay is formed. No control message is exchanged among peers for overlay maintenance. We present a combination of infrastructure-centric and application end-point architecture. The infrastructure-centric architecture refers to a tree controller, named DAg-master, which is responsible for tree/overlay administering and maintenance. The application end-point architecture refers to video sharing, streaming and adaptation by the participating resourceful peers. The motivation for this work is based on the experiences and lessons learned so far about developing a video adaptation system for heterogeneous devices. In this article, we present our architecture and some experimental evaluations supporting the design concept for overlay video streaming and online adaptation.

基于H.264的高分辨率序列帧内预测的改进算法

针对高清视频序列帧内预测的编码特点,得出禁用Intra4×4预测模式,使用Intra8×8和Intra16×16模式进行亮度预测,可显著提高编码速度,同时码率和SNR基本不变。基于上述结论,提出一种新的帧内预测快速算法。该算法在帧内预测之前进行预判决,从Intra8×8和Intra16×16中选择一种预测模式,从而减少了算法复杂度。实验结果表明,算法在码率只有少许增加的情况下,编码速度提高了27.8%,SNR值基本不变。     

QoE management for video conferencing applications

We introduce a framework for managing the QoE of videos coded with the H.264 codec and transmitted by video conferencing applications through limited bandwidth networks. We focus our study on the medium-motion videos with QCIF, CIF, and VGA resolutions, the most pervasive video formats used by video conferencing applications across the Internet and cellular telephony systems. Using subjective tests for measuring the level of video quality perceived by end users, we expose the relation between the main influential video parameters and the quality experienced by end users. Furthermore, after investigating the effect of different frame rates and compression levels on video streaming bit rate, and consequently on QoE, we propose a QoE control mechanism for limited-bandwidth situations. A congestion control technique is also introduced in this paper and used in simulations for verifying the efficiency of the proposed QoE management algorithm and to implement this algorithm for practical applications.     

Streaming of scalable h.264 videos over the Internet

To investigate the benefits of scalable codecs in the case of rate adaptation problem, a streaming system for scalable H.264 videos has been implemented. The system considers congestion level in the network and buffer status at the client during adaptation process. The rate adaptation algorithm is content adaptive. It selects an appropriate substream from the video file by taking into account the motion dynamics of video. The performance of the system has been tested under congestion-free and congestion scenarios. The performance results indicate that the system reacts to congestion properly and can be used for Internet video streaming where losses occur unpredictably.

Fast adaptive termination mode selection for H.264 scalable video coding

Although scalable video coding can achieve coding efficiencies comparable with single layer video coding, its computational complexity is higher due to its additional inter-layer prediction process. This paper presents a fast adaptive termination algorithm for mode selection to increase its computation speed while attempting to maintain its coding efficiency. The developed algorithm consists of the following three main steps which are applied not only to the enhancement layer but also to the base layer: a prediction step based on neighboring macroblocks, a first round check step, and a second round check step or refinement if failure occurs during the first round check. Comparison results with the existing algorithms are provided. The results obtained on various video sequences show that the introduced algorithm achieves about one-third reduction in the computation speed while generating more or less the same video quality.

一种改进的快速H.264/AVC帧内预测Pan算法

对基于边缘方向直方图的快速帧内预测Pan算法进行了改进,应用了帧内Intra_4×4和Intra_16×16块类型选择以及4×4亮度块模式选择提前中止技术。实验结果表明,该方法在保证图像失真度和码率性能的前提下,单帧编码时间较Pan算法减少了29.093%,较大幅度地加快了帧内模式决策速度。     

Mixed architectures for H.264/AVC digital video transrating

In this paper, we investigate transrating architectures for H.264/AVC video streams. Basic architectures are presented with their strengths and weaknesses. None of the existing architectures provide an appropriate solution for H.264/AVC transrating with an optimal balance between visual quality and complexity. In order to find such an appropriate solution, we propose the use of mixed transrating architectures. These architectures combine different transrating techniques which are applied depending on the picture/macroblock type. The intra-predicted pictures are decoded and re-encoded, while open-loop transrating or transrating with compensation is applied to motion-compensated pictures. Performance results show that the mixed architecture which applies spatial compensation to motion-compensated pictures gives rate-distortion results which approach the cascade of decoder and re-encoder with a complexity only slightly higher than the open-loop transrater. Adding temporal compensation for motion-compensated pictures further improves the visual quality, albeit to a lower extent, at the expense of increased complexity.

基于感知运动能量模型的MPEG-21数字项适配

最新的MPEG-21标准定义了一个统一的多媒体框架,其目标是使多媒体资源能在异构网络和终端上进行透明传输和得到充分利用。多媒体适配(Multimedia Adaptation)技术作为实现上述目标的关键技术得到了越来越多的研究。本文将感知运动能量模型与MPEG-21数字项适配框架相结合,研究和实现了基于感知运动能量的H．264／AVC视频丢帧适配技术。本文的研完工作有两个方面的优点：一方面,感知运动能量模型的使用将丢帧适配引起的运动抖动减至最小,保证了较高的用户视觉上的主观感知质量;另一方面,数据处理能力和资源受限的适配节点不需了解具体的H．264／AVC编码语法结构和编解码算法,就能方便地执行丢帧操作,实现了独立于媒体编码格式的视频适配机制,提高了多媒体适配系统的灵活性和可扩展性。     

HDS, a real-time multi-DSP motion estimator for MPEG-4 H.264 AVC high definition video encoding

H.264 AVC video compression standard achieves high compression rates at the cost of a high encoder complexity. The encoder performances are greatly linked to the motion estimation operation which requires high computation power and memory bandwidth. High definition context magnifies the difficulty of a real-time implementation. EPZS and HME are two well-known motion estimation algorithms. Both EPZS and HME are implemented in a DSP and their performances are compared in terms of both quality and complexity. Based on these results, a new algorithm called HDS for Hierarchical Diamond Search is proposed. HDS motion estimation is integrated in a AVC encoder to extract timings and resulting video qualities reached. A real-time DSP implementation of H.264 quarter-pixel accuracy motion estimation is proposed for SD and HD video format. Furthermore HDS characteristics make this algorithm well suited for H.264 SVC real-time encoding applications.     

Chaos-based selective encryption for H.264/AVC

Encryption techniques are usually employed to maintain the secrecy of the video streams transmitted via a public network. However, full encryption using strong cryptographic algorithms is usually not necessary if the purpose is to destroy the commercial value by preventing pleasant viewing. For this purpose, selective encryption is preferred as its operating efficiency is higher. Here, a chaos-based selective encryption scheme implemented on the H.264/AVC standard is proposed. The scheme employs multiple Rényi chaotic maps to generate a pseudorandom bit sequence which is used to mask the selected H.264/AVC syntax elements. It provides sufficient protection against full reconstruction while keeping the format compliance property so as not to cause decoding error without the key. The operating efficiency is high due to the low computational complexity of the Rényi chaotic map, as justified by the simulation results using video clips at various resolutions. Moreover, the security analyses show that the proposed algorithm is highly sensitive to the secret key and possesses good perceptual security.