Empirical evaluation of H.264/SVC streaming in resource-constrained multihomed mobile networks

Nomadic users of streamed multimedia content in mobile networks are often faced with resource-constrained network paths that suffer from low bandwidth. Streaming high-quality video in such a challenging scenario demands a set of highly adaptive schemes, which have not been sufficiently explored in particular for the emerging H.264 Scalable Video Coding (H.264/SVC) standard. In this paper, we empirically investigate the performance of streaming H.264/SVC scalable video streams to users in multihomed mobile networks containing multiple available transmission paths. Previous work has demonstrated the feasibility of aggregating bandwidth of multiple paths to deliver video streams when no single, sufficiently high bandwidth path is available. We focus on evaluating the enhanced performance of multipath bandwidth-aggregation streaming by exploiting a quality-layers based, H.264/SVC-specific packet prioritisation scheme for quality-aware multipath packet scheduling and selective packet dropping in case of bandwidth shortage even after aggregation. Additionally, we explore a base-layer rate control scheme for H.264/SVC delivery in ultra-low bandwidth environments. Through extensive experimentation on a realistic hardware-based testbed, we obtain a comprehensive and insightful understanding of the behaviour of H.264/SVC streams when transmitted across multiple paths in mobile networks. We quantify the improvements offered by the use of H.264/SVC-specific packet prioritisation schemes compared with an existing generic scalable video prioritisation scheme, and the benefits by the use of base-layer rate control in ultra-low bandwidth situations. The performance of the multipath streaming schemes is further compared with that of an ideal single high bandwidth path. We also identify the remaining challenges that must be overcome if such streaming schemes are to offer performance close to that of the ideal single high bandwidth path.     

Priority-based Media Delivery using SVC with RTP and HTTP streaming

Media delivery, especially video delivery over mobile channels may be affected by transmission bitrate variations or temporary link interruptions caused by changes in the channel conditions or the wireless interface. In this paper, we present the use of Priority-based Media Delivery (PMD) for Scalable Video Coding (SVC) to overcome link interruptions and channel bitrate reductions in mobile networks by performing a transmission scheduling algorithm that prioritizes media data according to its importance. The proposed approach comprises a priority-based media pre-buffer to overcome periods under reduced connectivity. The PMD algorithm aims to use the same transmission bitrate and overall buffer size as the traditional streaming approach, yet is more likely to overcome interruptions and reduced bitrate periods. PMD achieves longer continuous playback than the traditional approach, avoiding disruptions in the video playout and therefore improving the video playback quality. We analyze the use of SVC with PMD in the traditional RTP streaming and in the adaptive HTTP streaming context. We show benefits of using SVC in terms of received quality during interruption and re-buffering time, i.e. the time required to fill a desired pre-buffer at the receiver. We present a quality optimization approach for PMD and show results for different interruption/bitrate-reduction scenarios.     

Technique for authenticating H.264/SVC and its performance evaluation over wireless mobile networks

In this paper, a bit stream-based authentication scheme for H.264/Scalable Video Coding (SVC) is proposed. The proposed scheme seamlessly integrates cryptographic algorithms and Erasure Correction Codes (ECCs) to SVC video streams such that the authenticated streams are format compliant with the SVC specifications and preserve the three-dimensional scalability (i.e., spatial, quality and temporal) of the original streams. We implement our scheme on a smart phone and study its performance over a realistic bursty packet-lossy wireless mobile network. Our analysis and experimental results show that the scheme achieves very high verification rates with lower communication overhead and much smaller decoding delay compared with the existing solutions.     

MIMO系统中的H.264/SVC数据流抽取和重组算法

为了使H.264可分级视频编码(SVC)生成的数据流分割为多个子数据流,便于在多输入多输出(MIMO)无线网络的不同子信道上传输以提高视频传输速率,提出了一个SVC数据流抽取和重组算法.在发送端,该算法利用SVC数据流的分层结构,将其中的基本层和增强层抽取为多个子数据流,并保持基本层子数据流能够独立解码.在接收端,该算法将接收到的子数据流重组成可解码的SVC数据流.实验证明该算法能充分利用MIMO系统提供的高带宽,并具有较低的冗余度和较好的灵活性.     

H.264 video transmissions over wireless networks: Challenges and solutions

Multimedia video streaming is becoming increasingly popular. Using multimedia services, there are more and more users in end-system over wireless networking environment. H.264/AVC is now the standard for video streaming because of its high compression efficiency, robustness against errors and network-friendly features. However, providing the desired quality of service or improving the transmission efficiency for H.264 video transmissions over wireless networks present numbers of challenges. In this paper, we consider those challenges and survey existing mechanisms based on the protocol layers they work on. Finally, we address some open research issues concerning for H.264 video transmission in wireless networks.     

Efficient block-based transparent encryption for H.264/SVC bitstreams

Taking advantage of the inter-layer prediction technique used in H.264/scalable video coding (H.264/SVC), in this paper we propose an efficient block-based encryption scheme (BBES) for encrypting H.264/SVC enhancement layers (ELs). BBES operates in three modes, namely, Intra-MB mode, Group-MB mode and 4Group-MB mode. All the three modes are effective in securing ELs, preserve the “adaptation-transparent” property of H.264/SVC, and are format-compliant to the H.264/SVC bitstream format specifications. Moreover, Intra-MB and Group-MB modes also possess the property we termed as “transcoding transparency”. Experimental results indicate that BBES has low computational complexity and small compression overhead. Thus, BBES is suitable for transparent encryption of H.264/SVC bitstreams in which ELs are encrypted but base layers are left in cleartext.     

面向无线网络的可伸缩视频编码传输策略*

针对现有面向无线网络的可伸缩视频编码(Scalable Video Coding, SVC)传输策略未能充分考虑失真和能耗的问题,提出了一种基于失真和节点能耗最小化的SVC传输策略。该策略在分析SVC的编码失真、传输过程中的丢包失真的基础上,计算了接收端的视频失真总和;通过计算SVC传输系统的功率,对无线网络中的节点能耗进行了分析。然后综合考虑了能耗、传输时间及质量要求,将SVC的传输策略转化为一个优化问题,进而得到最优的SVC编码参数,在获得较优视频质量的前提下实现了SVC的可靠传输。仿真实验结果表明,与目前典型的SVC传输策略相比,该策略不但有效降低了SVC传输过程中的平均失真,而且在相同的能量消耗水平下,获得了更好的视频质量。     

H.264码流结构的分析

H.264是新一代视频编码标准,具有广泛的应用前景。本文主要研究了H.264码流的问题。首先,介绍了H.264的简单框架;其次,对码流结构进行了分析,并概括出了码流结构图;最后,结合一个简单试验,给出了从H.264码流中取得图像宽度和高度的方法。     

基于H.264可伸缩视频流的自适应媒体播放算法

为了应对H.264可伸缩视频编码（SVC）应用中网络特性的波动,提出了一种预测播放中断与缓冲区溢出风险进行及早调节的自适应媒体播放(AMP)算法。该算法估算网络流量与视频图像组（GOP）结构中各帧长度用于风险预测,通过K步调节过程实现良好的调节平滑性与速度,并利用SVC的可伸缩性尽量减少溢出带来的质量损失。仿真结果表明,该算法在抑制播放中断、处理缓冲区溢出与抖动性能等方面,优于现行的平滑AMP与常规AMP算法。     

基于H.264/SVC的率失真优化算法的改进

在H.264/SVC中误差扩散对视频流质量的影响最大,为了减小误差扩散,对H.264/SVC的空域分层编码和时域分层编码的率失真优化进行了研究,将码率分配和时间级函数的设定与时域分层编码的率失真优化相结合,提出了一种改进算法。对一个序列在不同丢包率下进行测试仿真,测试仿真结果表明,改进后的算法在丢包率和QP相同的情况下,有效地控制了码率的增加,提高了全局的率失真性能。     

Fast mode decision algorithm for H.264/SVC enhancement layer

Scalable video coding (SVC) has been standardized to extend the capabilities of the H.264 advanced video coding (AVC). The SVC can compress several video sequences of various resolutions as a single bit-stream. In the SVC enhancement layer, for Joint Scalable Video Model (JSVM) software implementation, an exhaustive mode decision process based on the base layer mode predictions is performed to obtain the best mode for each macroblock (MB). This technique may achieve a higher coding efficiency; however, it induces a significant computational complexity in the encoding engine. In order to speedup the SVC encoder, a fast mode decision algorithm was proposed in this paper. In other words, our aim was to decrease the number of candidate modes to reduce the computational complexity and maintain the same level of coding efficiency, this approach used the spatial and temporal correlation between MB situated at the enhancement layer and its co-located MB at the base layer. Our statistical analyses were made using several HD sequences with different motion characteristics. Experimental results show a significant improvement in terms of time encoding which is a major constraint for any real-time implementation. However, this gain is accompanied with an acceptable loss in video quality and a tolerable bit rate increase for most media supports. In fact, our proposed algorithm permits a major improvement that can reach up to 64.9 % in terms of computational effort. This gain will induce an average loss yield to 10.5 or 13.87 % that is comparable to the 13.12 % of the He Li’s algorithm with an acceptable loss in terms of subjective video quality.     

基于H.264 SVC的视频分层加密算法研究

随着可伸缩视频编码SVC(Scalable Video Coding)的普及,针对可伸缩视频的安全问题也越来越受到重视。目前大部分加密方案都是针对H.264/AVC编码标准来设计的。分析SVC新采用的技术,并率先提出了一种针对其特点的新的分层加密方案。该方案选取不同以往的视频关键信息,如层间预测运动向量,质量可分级关键帧等作为加密对象,根据所选信息的类型,结合用户所需求的安全等级,进行算法设计。试验结果表明该方案具有加密效果好、密钥量较低、实时性高等优点,并可以适应不同安全性需求的应用场合。     

基于H.264/SVC的数字水印方案设计

可伸缩视频技术以及数字水印技术是当前多媒体应用和版权保护研究中的一个热点。针对H.264SVC可伸缩视频压缩编码,提出基于DCT系数结合密钥控制的视频水印方案,加入密钥更提高了安全性。数字水印经过预处理嵌入DCT系数,基于HVS理论结合密钥选择合适的嵌入位置。水印在视频编码的同时完成嵌入,可盲检测,并利用SVC视频的空间上分辨率多层结构增大嵌入容量和鲁棒性。实验结果显示,在不可感知性和鲁棒性方面达到了不错的效果,能抵抗一些噪声和攻击。     

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.     

Architectures for Fast Transcoding of H.264/AVC to Quality-Scalable SVC Streams

The scalable extension of H.264/AVC (SVC) was recently standardized, and offers scalability at a minor penalty in rate-distortion efficiency when compared to single-layer H.264/AVC coding. In SVC, a scaled version of the original video sequence can easily be extracted by dropping layers from the stream. However, most of the video content nowadays is still produced in a single-layer format. While decoding and reencoding is a possible solution to introduce scalability in the existing bitstreams, this is an approach which requires a tremendous amount of time and effort. In this paper, we show that transcoding can be used to intelligently derive scalable bitstreams from existing single-layer streams. We focus on SNR scalability, and introduce techniques that are able to create multiple quality layers in the bitstreams. We also discuss bitstream rewriting from SVC to H.264/AVC, and examine how our newly proposed architectures can benefit from the changes that were introduced for bitstream rewriting. Architectures with different rate distribution flexibility and computational complexity are discussed. Rate-distortion performance of transcoding is shown to be comparable to that of reencoding at a fraction of the time needed for the latter.     

H.264/SVC mode decision based on mode correlation and desired mode list

Design of video encoders involves implementation of fast mode decision (FMD) algorithm to reduce computation complexity while maintaining the performance of the coding. Although H.264/scalable video coding (SVC) achieves high scalability and coding efficiency, it also has high complexity in implementing its exhaustive computation. In this paper, a novel algorithm is proposed to reduce the redundant candidate modes by making use of the correlation among layers. A desired mode list is created based on the probability to be the best mode for each block in base layer and a candidate mode selection in the enhancement layer by the correlations of modes among reference frame and current frame. Our algorithm is implemented in joint scalable video model (JSVM) 9.19.15 reference software and the performance is evaluated based on the average encoding time, peak signal to noise ration (PSNR) and bit rate. The experimental results show 41.89% improvement in encoding time with minimal loss of 0.02 dB in PSNR and 0.05% increase in bit rate.     

H.264/SVC比特自适应分配的等级B帧码率控制算法

为减少码率控制中实际输出码率与目标码率之间的误差,改善视频序列编码尾部质量下降的缺陷,同时针对可伸缩视频编码中码率控制算法的不足,提出一种自适应比特分配的码率控制算法。算法基于对根据相邻图像帧之间的相关性以及对恒定质量的考虑,在图像组(GOP)之间平均分配目标比特,而在GOP内部则根据编码复杂度自适应分配目标比特,同时适当调整初始量化参数(QP),再根据目标比特分别计算P帧、B帧的QP。对不同的视频序列进行了实验测试,其结果验证了算法的准确性和有效性。     

Efficient DRM mechanism of scalable contents based on H.264/SVC in convergence environment

This paper proposes a scalable video coding (SVC) DRM mechanism considering the convergence environment that redistributes the adaptive content for devices which may have different display size and computing capabilities between users or in the home network. The proposed SVC DRM mechanism uses the SVC content that is compressed by H.264/SVC scheme which has been standardized recently and encrypted by SVC encryption scheme so that each device gets a content of suitable level according to its own device capability. For the secure and efficient superdistribution of SVC content, moreover, this paper defines four requirements for SVC DRM and proposes a mechanism which satisfies these requirements by using another license called ‘Ticket’. In addition, our system allows devices to redistribute the contents freely in the home network since the devices in the domain are managed by the domain key.     

Error robust scalable audio streaming over wireless IP networks

Streaming high-fidelity audio over wireless Internet protocol (IP) networks is a challenging task because the networks present not only packet losses, but also residual bit errors. These losses and errors have severe adverse effect on the compressed audio bitstream. To solve this problem, this paper introduces error resilience in conjunction with error protection for scalable audio streaming over wireless networks. Specifically, error resilience is achieved by performing bitstream data partitioning and reversible variable length coding in the audio coder. Error protection is provided by layered product channel code to simultaneously handle packet losses and residual bit errors. Both the row and column codes of the product code provide unequal error protection for different layers of the audio bitstream by considering the characteristics of the scalable audio. Rate-distortion optimization is performed to determine the best source-channel coding tradeoff that minimizes the average expected end-to-end distortion. Simulation results demonstrate the effectiveness of our proposed approach.