Restricted H.264/AVC video coding for privacy protected video scrambling

The issue of personal privacy has garnered significant attention with the extensive application of video surveillance systems. Privacy region scrambling is an effective method to protect privacy in video. To ensure that nonprivacy regions are not affected by scrambling, particular methods must be taken to prevent drift error in privacy protected video scrambling. However, existing methods have significantly reduced the coding efficiency. In this paper, we focus on improving coding efficiency while preventing drift error in privacy protected H.264/AVC video scrambling, which is the state-of-the-art coding standard. A restricted video coding scheme is proposed, which involves three parts of Mode Restricted Intra Prediction (MRIP), Search Window Restricted Motion Estimation (SWRME) and Boundary Strength Restricted Deblocking Filtering (BSRDF). Experimental results show that the proposed restricted video coding scheme prevents drift error with higher coding efficiency than others.     

A novel selective encryption scheme for H.264/AVC video with improved visual security

As cloud storage becomes more popular, concerns about data leakage have been increasing. Encryption techniques can be used to protect privacy of videos stored in the cloud. However, the recently proposed sketch attack for encrypted H.264/AVC video, which is based on the macroblock bitstream size (MBS), can generate the outline images of both intra-frames and inter-frames from a video encrypted by most existing encryption schemes; thus, the protection of the original video may be considered a failure. In this paper, a novel selective encryption scheme for H.264/AVC video with improved visual security is presented. Two different scrambling strategies that do not destroy the format compatibility are proposed to change the relative positions between macroblocks in intra-frames and inter-frames respectively, which in turn substantially distort the sketched outline images so that they do not disclose meaningful information. Moreover, the sign bits of non-zero DCT coefficients are encrypted to contribute to the visual security of our scheme, and an adaptive encryption key related to the intra prediction mode and the DCT coefficient distribution of each frame is employed to provide further security. The experimental results show that our encryption scheme can achieve a better visual scrambling effect with a small adverse impact on the video file size. Furthermore, the security analysis demonstrates that our scheme can successfully resist the MBS sketch attack compared with other related schemes. The proposed method is also proven secure against some other known attacks.     

An efficient motion vector coding scheme based on minimum bitrateprediction

Motion vector coding efficiency is becoming an important issue in low bitrate video coding because of its increasing relative bit portion. This work presents a new motion vector coding technique based on minimum bitrate prediction. In the proposed scheme, a predicted motion vector is chosen from the three causal neighboring motion vectors so that it can produce a minimum bitrate in motion vector difference coding. Then the prediction error, or motion vector difference (MVD), and the mode information (MODE) for determining the predicted motion vector at a decoder are coded and transmitted in order. Sending bits for the MVD ahead of bits for the MODE, the scheme can minimize the bit amount for the MODE by taking advantage of the fact that the minimum bitrate predictor is used for motion vector prediction. Adaptively combining this minimum bitrate prediction scheme with the conventional model-based prediction scheme, more efficient motion vector coding can be achieved. The proposed scheme improves the coding efficiency noticeably for various video sequences.     

考虑视频内容的H.265/HEVC帧层码率分配算法

为了保证一定视频质量下编码器输出的码率符合给定的目标码率,提出一种考虑视频内容特性的H.265/HEVC帧层码率分配算法。首先从率失真理论分析的角度推导出影响输出码率的主要因素,然后根据视频编码原理,预测出帧内容复杂度参数,从而建立一种更有效的帧层码率分配算法。实验结果表明,所提算法可以使帧层目标码率与编码码率保持更好的一致性,且重构视频质量平均提高了0.103 dB。     

A joint signal processing and cryptographic approach to multimedia encryption.

In recent years, there has been an increasing trend for multimedia applications to use delegate service providers for content distribution, archiving, search, and retrieval. These delegate services have brought new challenges to the protection of multimedia content confidentiality. This paper discusses the importance and feasibility of applying a joint signal processing and cryptographic approach to multimedia encryption, in order to address the access control issues unique to multimedia applications. We propose two atomic encryption operations that can preserve standard compliance and are friendly to delegate processing. Quantitative analysis for these operations is presented to demonstrate that a good tradeoff can be made between security and bitrate overhead. In assisting the design and evaluation of media security systems, we also propose a set of multimedia-oriented security scores to quantify the security against approximation attacks and to complement the existing notion of generic data security. Using video as an example, we present a systematic study on how to strategically integrate different atomic operations to build a video encryption system. The resulting system can provide superior performance over both generic encryption and its simple adaptation to video in terms of a joint consideration of security, bitrate overhead, and friendliness to delegate processing.     

Secure transcoders for single layer video data

This paper considers the use of selective encryption systems for compressed video data that can support transcoding of the encrypted bit-streams without the need for decryption and re-encryption. The focus is on the use of the H.264 video codec. However, the concepts can be easily extended to any video coding standard.I-frame encryption encrypts only the intra frames, making it suitable for use with modified interframe transcoders that operate only on P and B frames. These interframe transcoders are found to offer improved performance for un-encrypted data, due to the temporal propagation of the higher quality of I-frames. The operations of both interframe open loop transcoding and Fast Pixel Domain Transcoding (FPDT) are unaffected by I-frame encryption yielding identical results. However, the lack of I-frame data causes a significant drift problem when I-frame encryption is used with a more complete Cascaded Pixel Domain Transcoder (CPDT). A modified CPDT is proposed, called Intra Block Copy (IBC) transcoding, which offers improved performance at the expense of a reduced range of possible output bitrates.Sign bit encryption systems such as Real-time Video Encryption Algorithm (RVEA) offer improved security compared to I-frame encryption. However transcoding this data can result in some sign bits being omitted causing a loss of cipher synchronization. A novel sign bit encryption technique called Synchronous Video Encryption Algorithm (SVEA) is proposed that preserves the cipher synchronization. While the operation of open loop transcoding systems is unaffected, the encryption interferes with the drift compensation in the more complex transcoders, leading to reduced performance.     

Transparent encryption with scalable video communication: Lower-latency,CABAC-based schemes

Selective encryption masks all of the content without completely hiding it, as full encryption would do at a cost in encryption delay and increased bandwidth. Many commercial applications of video encryption do not even require selective encryption, because greater utility can be gained from transparent encryption, i.e. allowing prospective viewers to glimpse a reduced quality version of the content as a taster. Our lightweight selective encryption scheme when applied to scalable video coding is well suited to transparent encryption. The paper illustrates the gains in reducing delay and increased distortion arising from a transparent encryption that leaves reduced quality base layer in the clear. Reduced encryption of B-frames is a further step beyond transparent encryption in which the computational overhead reduction is traded against content security and limited distortion. This spectrum of video encryption possibilities is analyzed in this paper, though all of the schemes maintain decoder compatibility and add no bitrate overhead as a result of jointly encoding and encrypting the input video by virtue of carefully selecting the entropy coding parameters that are encrypted. The schemes are suitable both for H.264 and HEVC codecs, though demonstrated in the paper for H.264. Selected Content Adaptive Binary Arithmetic Coding (CABAC) parameters are encrypted by a lightweight Exclusive OR technique, which is chosen for practicality.     

On re-composition of motion compensated macroblocks for DCT-based video transcoding

To achieve portability between different kinds of encoding formats and network environments, heterogeneous video transcoding becomes a key technique for reducing the bitrate of a previously compressed video signal. A frame-skipping transcoder is often used to avoid an unacceptable picture quality when high transcoding ratio is required. Due to high computational complexity and quality degradation introduced by conventional frame-skipping transcoders, a DCT-based video frame-skipping transcoder has been proposed recently. However, the transcoding process of the motion compensated macroblocks in the DCT domain becomes the bottleneck since IDCT and DCT processes are required. In this paper, we propose a new architecture of the frame-skipping transcoder to reduce the computational complexity of motion compensated macroblocks in the frame-skipping process. The new architecture transcodes the dominant region of a motion compensated macroblock in the DCT domain by making use of the DCT coefficients of the incoming bistream and some pre-computed shift operators. By using a shifted version of the dominant vector, the re-encoding error introduced in the dominant region can be avoided. On the other hand, an adaptive transcoding architecture to transcode the boundary regions of MC marcoblocks and a way to perform error compensation are proposed. This architecture can further speed up the transcoding process of the motion compensated macroblocks. Half pixel accuracy related to our proposed frame skipping transcoder is also addressed. Experimental results show that, as compared to the conventional or DCT-based transocders, the new architecture is more robust to noise, gives rise to fewer requantization errors, and requires simple computational complexity.     

DCT-based video downscaling transcoder using split and merge technique.

For a conventional downscaling video transcoder, a video server has firstly to decompress the video, perform downscaling operations in the pixel domain, and then recompress it. This is computationally intensive. However, it is difficult to perform video downscaling in the discrete cosine transform (DCT)- domain since the prediction errors of each frame are computed from its immediate past higher resolution frames. Recently, a fast algorithm for DCT domain image downsampling has been proposed to obtain the downsampled version of DCT coefficients with low computational complexity. However, there is a mismatch between the downsampled version of DCT coefficients and the resampled motion vectors. In other words, significant quality degradation is introduced when the derivation of the original motion vectors and the resampled motion vector is large. In this paper, we propose a new architecture to obtain resampled DCT coefficients in the DCT domain by using the split and merge technique. Using our proposed video transcoder architecture, a macroblock is splitted into two regions: dominant region and the boundary region. The dominant region of the macroblock can be transcoded in the DCT domain with low computational complexity and re-encoding error can be avoided. By transcoding the boundary region adaptively, low computational complexity can also be achieved. More importantly, the re-encoding error introduced in the boundary region can be controlled more dynamically. Experimental results show that our proposed video downscaling transcoder can lead to significant computational savings as well as videos with high quality as compared with the conventional approach. The proposed video transcoder is useful for video servers that provide quality service in real-time for heterogeneous clients.     

一种面向HEVC的并行码率控制算法

视频通信时通常带宽有限,为了能在规定的目标码率下获得尽可能高质量的解码图像,需要在视频编码时进行码率控制.目前针对HEVC的并行编码以及对应码率控制已成为研究热点,现有并行结构下的平均比特率控制算法受到帧间依赖性的约束,待编码帧无法及时获得与其并行编码帧的实际比特数,因此本文算法通过预测并行帧的实际比特数来进行码率控制,并在此基础提出了自适应调整帧层量化参数补偿值.仿真结果表明,相比已有算法,前者减少码率误差约为3.38％,后者可提高PSNR约为0.204 dB同时减少约0.3％的码率误差.     

基于H.264的新型视频加密算法

本文提出了一种新的基于H.264标准的视频加密算法结构。使用改进的FMO机制(advanced-FMO mechanism)将具有相关性的宏块打入不同的Slice中,通过对FMO子图的加密达到对整个视频内容进行加密的目的。本文提出的加密算法具有很高的实时性,加密过程可以和编码过程并行执行。同时本算法还可以和传统的加扰算法结合,进一步提高视频的加密效果。     

A Novel Method for Bitrate Control within Macroblocks Using Kalman and FIR Filters

In this letter, we propose a novel bitrate control, using both Kalman and FIR filters, based on a Hamiltonian analysis with respect to the amount of bits from each macroblock, in an encoding of a general video codec such as H.264/AVC. Since the proposed bitrate control is based on the simple computation of an optimal control method based on the Hamiltonian analysis, it is not necessary to use additional computation, such as a DCT or quantization, to estimate the bits for bitrate control. As a result, the proposed algorithm can be applied to single‐pass encoding and can provide sufficient encoding speed with respect to various applications, even those requiring real‐time control.     

智能电网中面向隐私保护的数据聚合算法

随着智能电网(SG)的迅速发展,其安全和效率受到广泛关注。在SG中,居住区域内多个智能电表(SM)设备将感测数据传输至控制中心,使得用户数据需经过一些中间节点才到达控制中心。而通过挖掘用户相关数据(URD),攻击者能够窃取用户的习惯和行为,因此,需要保护用户的隐私。为此,提出面向隐私保护的数据聚合(PPDA)算法。PPDA算法利用群位置隐私(GLP)掩饰由SM产生的数据,并利用Paillier加密系统对用户数据进行保护。此外,PPDA算法无需任何安全信道。仿真结果表明,提出的PPDA算法能够防御偷听攻击和勾结攻击,并控制了计算开销。     

基于熵编码的立体视频加密与信息隐藏算法

针对立体视频的安全性,该文提出一种基于熵编码的立体视频加密与信息隐藏算法。首先,结合立体视频编码结构,分析误差漂移的物理机制,并根据立体视觉掩蔽效应,确定左右视点的加密帧和隐秘信息待嵌入帧。其次,在基于上下文自适应二进制算术编码(CABAC)的熵编码中,通过等长码字替换技术,实现立体视频的加密和信息隐藏。实验结果表明,视频码流经加密与信息隐藏之后格式兼容、比特率不变,视频感知质量无明显下降,在计算复杂度和码率增加率上有显著优势。     

一种基于混沌置乱的视频实时加密方法

文章针对传统的加密算法难以满足数据量大、实时性要求高的数字视频的加密需要的问题,设计了一种基于混沌置乱的视频实时加密方法.该方法先计算出视频图像的特征值,再通过该特征值生成不同的混沌序列,然后利用这些不同的混沌序列实现对视频的运动矢量与QDCT块置乱.该方法具有加密实时性好,对视频输出速率影响小的特点.     

基于离散分数阶角变换与关联混沌映射的双图像加密算法

为了实现对两个明文进行同步安全加密,提出了联合离散多参数分数阶角变换与低维映射的双图像加密算法.基于离散余弦变换(DCT)与Zigzag扫描建立了复合系数矩阵模型,通过反离散余弦变换(IDCT)将两个明文融合成一幅图像;通过耦合Logistic映射,利用明文像素均值与外部密钥计算其初始条件值,并迭代该耦合映射,输出2个随机序列;分别对这2个随机序列进行排序,设计位置数组扰乱机制对复合明文进行置乱;将置乱密文分解为2个新分量,利用Logistic映射与初始明文分别生成混沌随机与调制相位掩码,将2个新分量融合成临时密文;基于离散分数角变换构建了新的2D多参数分数阶角变换,设计加密模型并完成图像加密.结果表明,与已有双图像加密机制相比所提算法的保密性更佳,有更好的抗明文攻击特性.     

New architecture for dynamic frame-skipping transcoder

Transcoding is a key technique for reducing the bit rate of a previously compressed video signal. A high transcoding ratio may result in an unacceptable picture quality when the full frame rate of the incoming video bitstream is used. Frame skipping is often used as an efficient scheme to allocate more bits to the representative frames, so that an acceptable quality for each frame can be maintained. However, the skipped frame must be decompressed completely, which might act as a reference frame to nonskipped frames for reconstruction. The newly quantized discrete cosine transform (DCT) coefficients of the prediction errors need to be re-computed for the nonskipped frame with reference to the previous nonskipped frame; this can create undesirable complexity as well as introduce re-encoding errors. In this paper, we propose new algorithms and a novel architecture for frame-rate reduction to improve picture quality and to reduce complexity. The proposed architecture is mainly performed on the DCT domain to achieve a transcoder with low complexity. With the direct addition of DCT coefficients and an error compensation feedback loop, re-encoding errors are reduced significantly. Furthermore, we propose a frame-rate control scheme which can dynamically adjust the number of skipped frames according to the incoming motion vectors and re-encoding errors due to transcoding such that the decoded sequence can have a smooth motion as well as better transcoded pictures. Experimental results show that, as compared to the conventional transcoder, the new architecture for frame-skipping transcoder is more robust, produces fewer requantization errors, and has reduced computational complexity.     

一种基于FMO置乱的视频加密算法研究

通过分析H．264提出的灵活宏块排序（FMO）的特点,提出了一种随机置乱FMO—map的视频加密方案。此方案通过产生一个随机顺序的码表来置乱FMO—map来达到视频流加密的效果,另外将加密后的随机置乱码表并行输出。通过分析证明此方案在安全性、压缩比改变率和计算复杂度方面都具有良好的性能,能使视频图像的传输具有较好的安全性和实时性。     

基于双重水印加密和SVD的视频水印方案

针对视频水印的安全性,提出了一种基于双重水印加密和SVD的视频水印方案。该方法首先将水印图像经Arnold置乱,对置乱后的水印通过Chebyshev混沌映射进行加密,保障水印的安全性;然后,对视频关键帧进行三级小波分解,利用SVD对几何失真的不变性,将水印3次嵌入到LL3、HL3和LH3中。实验表明该方案对高斯噪声、MPEG压缩、剪切等具有较高的鲁棒性。     

一种适合于H.264实时视频传输的新型加密方案

H.264是由ITU-T和ISO/IEC联合制定的最新视频编码标准,其安全加密技术正成为研究的热点.文章通过研究适合于H.264加密的侯选域,提出了一种加密与压缩相结合的新型视频加密方案,该方案包括崭新的CAVLC(基于上下文的自适应变长编码)与QTC(量化变换系数)加密同步,预测模式置乱和运动矢量置乱.理论分析和实验结果表明,此方案速度快,安全性高,传输误码鲁棒性较强,并对压缩比影响小.