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.

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.

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。     

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.     

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.     

一种针对H.264/AVC的帧间模式快速选择算法

为了进一步减小宏块的帧间预测误差,新的视频编码标准H.264/AVC采用了可变块划分运动估计,极大地增加了编码器的复杂度.针对此问题,提出了一种快速的帧间模式选择算法,该算法利用已编码相邻宏块的时间和空间相关性信息预先检测图像,对图像各区域可能采用的编码模式进行判定,从而大大简化了模式选择的过程.实验结果表明,算法可以在图像质量基本保持不变的基础上,有效地降低编码的复杂度.     

H.264与MPEG-4压缩编码标准的分析与比较

H．264和MPEG-4是新一代的视频压缩编码标准。详细讨论了这两个标准的编码结构和编码特点,针对这两个标准在流媒体以及视频会议应用中的不同性能,选取标准测试序列进行测试,根据标准测试序列的实验结果,对这两个标准的编码性质进行了量化的比较。得出同一码率下,MPEG-4不如H．264的性能优良,但MPEG-4是实现基于内容的压缩编码,其良好的兼容性、可靠性和灵活性,也有其不可忽略的作用,两种编码的各自特点决定了他们的应用领域。     

MPEG-4 to H.264 transcoding with frame rate reduction

In this paper, a temporal resolution reduction transcoding method that transforms an MPEG-4 video bitstream into an H.264 video bitstream is proposed. The block modes and motion vectors in the MPEG-4 bitstream are utilized in the H.264 encoder for the block mode conversion and motion vector interpolation methods. Four types of motion vector interpolation methods are proposed in order to avoid the use of brute-force motion estimation in H.264. According to the experimental results, the proposed methods achieve a 3∼4 times improvement in the computational complexity compared to the cascade pixel-domain transcoding method, while the PSNR (peak signal to noise ratio) is degraded by 0.2∼0.9 dB depending on the bitrates.

H.264帧内预测模式的快速选择算法

为了降低H.264标准中帧内预测模式选择的复杂度,提出一种快速的帧内预测方法.H.264采用率失真优化(RDO)算法,通过计算所有预测组合模式的率失真代价来确定宏块的最优编码模式,其计算复杂度非常大.提出的帧内预测快速选择方法利用宏块的绝对误差和(SAD)来缩小预测模式的范围,减少帧内预测的计算量,从而提高模式判别的速度.实验结果表明,在图像质量和码率基本保持不变的情况下,该算法使Ⅰ帧的编码速度提高约76%.     

H.264到AVS快速视频转码技术研究

通过深入对比和分析H.264 Main Profile和AVS-P2的L4.2两种视频编解码标准,本文提出一种快速实现H.264到AVS视频转码的技术,并对该转码技术进行软件实现。     

H.264帧内预测模式选择快速算法

帧内预测是H.264视频编码标准的重要组成部分。为了保证在图像质量和编码比特率大致不变的前提下,减少帧内预测模式选择的编码时间,提出了一种基于4′4块的纹理方向性和4′4块与16′16块之间的相关性并通过设置双阈值进行选择预测模式的快速算法。实验结果表明该算法与帧内预测编码的全搜索算法相比,编码时间节约了35%～40%,信噪比损失了0.03～0.1dB。     

H.264帧内预测快速模式选择

H.264/AVC视频编码标准中用率失真优化(RDO)方法为一个宏块(MB)判决最佳编码模式来提高编码效果,加大了算法复杂度并且计算冗余大。为了克服这一缺点,一种快速帧内预测模式选择算法被提出。在色度预测中,根据宏块的色度纹理复杂度,把原先的4种模式降到1或2种;在亮度16×16块模式判决中,根据最小哈达玛变换的绝对误差和(SATD)来选择最佳模式;在亮度4×4块模式判决中,该算法在9种模式中选择3种可能模式作为候选模式。通过比较16个4×4块总代价与1个16×16块的代价来选择最佳块选择模式,实验表明,该算法能在节省69%左右编码时间的情况下,比特率与峰值信噪比(PSNR)保持不变。     

一种用于H.264的快速帧内预测模式判别方法

提出了一种快速帧内预测模式判别的方法来减少H.264中帧内预测模式判别的时间。H.264采用拉格朗日率失真优化(RDO)模式判别方法来对帧内预测模式进行判别,但由于H.264提供了大量的帧内编码模式,使得计算量非常大,目的是在RD性能没有明显下降的情况下,减少帧内预测的计算量。提出的快速模式判别方法采用绝对变换差值和(SATD)以及绝对梯度和(SAG),来减少4×4和8×8块的帧内预测模式的数目,从而提高模式判别的速度。实验结果表明,该算法在编码增益减少不大的情况下,I帧的编码时间减少了50%~70%,整体的编码时间减少了大约10%~20%。     

Real time data hiding by exploiting the IPCM macroblocks in H.264/AVC streams

A new method for data hiding in H.264/AVC streams is presented. The proposed method exploits the IPCM encoded macroblocks during the intra prediction stage in order to hide the desired data. It is a blind data hiding scheme, i.e. the message can be extracted directly from the encoded stream without the need of the original host video. Moreover, the method exhibits the useful property of reusing the compressed stream for hiding different data numerous times without considerably affecting either the bit-rate or the perceptual quality. This property allows data hiding directly in the compressed stream in real time. The method perfectly suits to covert communication and content authentication 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.     

H.264/AVC先进视频编码研究

为了取得更高的图像压缩性能和更多的实用功能,ISO／IEC MPEG(运动图像专家组)和ITU-TVCEG(视频编码专家组)共同制订了一套新的视频编码标准H．264／AVC。介绍了H．264／AVC图像编解码系统的实现过程,对其采用的新技术进行了描述,最后将其与H．263和MPEG-4标准进行了性能对比。     

一种基于快速模式选择的H.264跳帧转码算法的研究

为使视频数据适应异构网络和不同终端设备,基于最新视频编码标准H.264的跳帧转码技术成为当前的研究热点。针对在H.264跳帧转码过程中,对所有帧间候选模式进行运动估计而耗费巨大计算资源等问题,在分析相邻帧对应宏块编码特性的基础上,提出一种基于宏块时域相关性的快速模式选择算法。该算法首先统计不同特性视频序列相邻帧对应宏块编码模式的相关性;选取相关性高的模式作为编码模式可选集合,以减少模式选择遍历数目;在对当前宏块进行编码时,根据前一帧对应宏块的模式从上述集合中选取模式进行遍历,以实现率失真优化算法的提前终止。实验结果表明,该算法在控制比特率增长4%的情况下,缩减编码时间近25%,说明算法在保证视频图像具有较好质量的前提下,能够有效降低算法的时间复杂度。     

H.264/AVC中CAVLC解码器的硬件设计与实现

设计了一种基于H.264标准的CAVLC解码器,码流输入单元采用桶形移位器,以实现单周期解一个句法元素,在各解码模块中采用码表分割、算术逻辑替代查表、零码字跳转等关键技术,在减少路径延迟和提高系统吞吐率的同时,节省了硬件开销。整个设计采用Verilog语言实现,在XILINX的ISE8.2开发环境下通过FPGA验证,使用Design Compiler在SMIC0.18μm CMOS单元库下综合,时钟最高频率可以达到165MHz。本设计可满足实时解码H.264高清视频的要求。     

H.264/AVC的自适应时域错误隐藏方法

针对视频传输时容易发生损坏或丢失的特点,为了更好地恢复图像质量,提出了基于H.264/AVC平台的自适应时域错误隐藏方法,该方法依据边界失真准则自适应转换两种隐藏方法,一种是初次隐藏,另一种是集成隐藏。集成隐藏采用自适应加权集成初次隐藏和增强隐藏。实验仿真结果表明方法改善了隐藏性能。