低复杂度空域错误隐藏算法

在无线网等不可靠信道传输视频中,针对包含边缘信息的宏块丢失带来的错误,提出了一种低复杂度的空间域错误隐藏算法,该算法根据周围已经接收到的宏块特征,估算丢失宏块中边缘方向,并按照边缘方向使用周围临近像素值进行插值,恢复出包含边缘的宏块;在插值过程中提出并采用了一种快捷的方向插值法。实验结果表明,该算法能有效地掩盖丢失宏块,比常规方法具有更好的掩盖效果与实时性。     

适用于增强层的帧间快速编码算法*

视频可伸缩视频编码方式有着较高的编码效率,然而也有着较高的编码时间代价,因此,结合可伸缩编码的特征来提高其编码速度显得很有必要。本文根据空间可伸缩编码的特征,提出了一种适合于增强层的帧间快速编码算法,具体来讲,如果基本层宏块采用帧内模式,则增强层对应宏块采用Intra-BL模式;否则,根据相关宏块模式的和采用不同的算法同时结合提前终止算法。实验证明,该算法在视频序列不太复杂或者复杂视频序列但是编码量化参数不太大的情况下,编码速度有着显著地提高,同时编码质量差别很小。     

基于空间相关性的复杂度可分级帧间模式选择

本文提出了一种针对H．264的复杂度可分级的帧间模式选择算法,该算法采用一张概率表将当前宏块的7种预测模式与相邻的上侧和左侧宏块的最优模式联系起来。对于每一种相邻宏块模式的组合情况,该表将当前宏块的7种预测模式按照出现概率的高低进行排序,从而可以确定最可能模式、次最可能模式等。在此基础上,调整候选模式数量以匹配终端平台不同的复杂度约束水平,同时又可以最大可能地保证最优模式处在所选择的部分模式子集中。该算法具有4个复杂度级别：40％,54％,70％和82％,实验证明该方法可以灵活有效地降低编码器复杂度,同时编码质量下降很小,不会影响主观效果。     

H.264/AVC中基于决策树的P帧快速模式选择（HHME2013第61号论文）

目的：H.264/AVC帧间预测编码需要对所有可能编码模式计算并比较率失真代价,众多的模式类型导致了P帧编码的计算复杂度非常高。本文提出了一种针对P帧的基于决策树的快速选择候选模式算法。方法：在对宏块进行16×16的帧间运动估计后,首先根据残差宏块中4×4全零系数块个数对部分宏块直接选择出候选模式;然后使用16个4×4块的SATD值,采用决策树分类方法对其余宏块选择候选模式。结果：由于只需对候选模式进行编码,因此有效降低了编码器的计算复杂度。实验结果表明,与原始全搜索编码算法相比,该算法对不同运动程度的视频序列获得了较一致的编码时间节省,同时平均峰值信噪比的损失和平均比特率的增加均较少。结论：本文提出了一种新的P帧帧间预测候选模式选择算法,根据帧间运动估计后的残差宏块信息,采用决策树方法对候选模式集进行分类。实验结果表明,该算法能在保证视频编码质量的前提下,有效地降低编码过程中的计算量,缩短编码时间。     

H.264/AVC中基于决策树的P帧快速模式选择

目的 H.264/AVC帧间预测编码需要对所有可能编码模式计算并比较率失真代价,众多的模式类型导致了P帧编码的计算复杂度非常高。为此提出一种针对P帧的基于决策树的快速候选模式选择算法。方法在对宏块进行16×16的帧间运动估计后,首先根据残差宏块中4×4全零系数块个数对部分宏块直接选择出候选模式;然后使用16个4×4块的变换域系数绝对值之和(SATD)值,采用决策树分类方法对其余宏块选择候选模式。结果由于只需对候选模式进行编码,因此有效降低了编码器的计算复杂度。实验结果表明,与原始全搜索编码算法相比,该算法对不同运动程度的视频序列获得了较一致的编码时间的节省,同时平均峰值信噪比的损失和平均比特率的增加均较少。结论新的P帧帧间预测候选模式选择算法,根据帧间运动估计后的残差宏块信息,采用决策树方法对候选模式集进行分类。实验结果表明,该算法能在保证视频编码质量的前提下,有效地降低编码过程中的计算量,缩短编码时间。     

基于多模式叠加的H.264时域隐藏算法

为在高误码环境下提高视频通信中重建图像的质量,根据最新H.264标准的特点,提出了一种基于多模式叠加的时域错误隐藏算法。该算法以不同的模式对丢失宏块进行4次掩盖,得到4个隐藏块,以各隐藏块的加权和作为丢失宏块的最终替代块。仿真结果表明,由于利用了宏块模式信息,该算法在不同测试序列及丢包率下的性能均优于传统叠加算法,显著提高了掩盖效果。     

Hybrid error concealments based on block content

We present a novel error-concealment method for MPEG-2 video decoders. Imperfect transmission of block-based compressed images may result in the loss of blocks, degrading the quality of the received video signal. Since an I-picture is used as a reference picture for forward and backward predictions of neighbouring pictures, transmission errors in an I-picture are propagated both spatially in the I-picture and temporally to P-/B-pictures, and thus may severely degrade the video signal, compared with the errors in P-/B-pictures. To minimise the quality degradation of the video signal, error concealment has been performed in I-pictures through adaptive spatial and temporal interpolations in the respective domains. Using edge information extracted from the neighbourhoods of the erroneous macroblocks, we categorise each erroneous macroblock (MB) based on the characteristics of neighbouring MBs. The categorised MB is reconstructed by the spatial or temporal error concealment methods selected by the category-dependent criteria reflecting the properties of the block content. The proposed technique solves blocky artefacts and blurring problems of existing error concealment methods and thus effectively conceals the lost blocks in an error video signal. Through computer simulations on damaged images, we show that the proposed method is robust to image characteristics and obtains better subjective quality than other error concealment methods.     

基于H.264的误码隐藏技术

为了在高误码环境下提高视频通信质量,提出一种改进的基于H.264的误码隐藏技术。对于帧内编码图像,根据图像直方图信息计算图像的光滑特性,然后自适应地选择线性插值的方法。对于帧间编码图像,根据不同大小块编码类型和多参考帧的特性,能够更准确地估计出丢失的MV,进行时域误码隐藏。实验表明,此方法同H.264参考软件JM11.0方法相比,具有更好的主客观图像恢复质量。     

A first approach to speeding-up the inter mode selection in MPEG-2/H.264 transcoders using machine learning

The H.264 standard achieves much higher coding efficiency than the MPEG-2 standard, due to its improved inter and intra prediction modes which come with a cost of higher computation complexity. Transcoding MPEG-2 video to H.264 is important to enable gradual migration to H.264. However, given the significant differences between the MPEG-2 and the H.264 coding algorithms, transcoding is much more complex and new approaches to transcoding are necessary. In this paper, we introduce and evaluate a low complexity macroblock partition mode decision algorithm, to be used as part of a high-efficient inter-frame prediction in MPEG-2 to H.264 transcoder. The proposed tools are used to compute an optimal MB coding mode decision with significantly reduced computational complexity. Specifically, we achieve the computational savings by using the following MB information coming from MPEG-2: the MB coding modes, the coded block pattern (CBPC) in MPEG-2, and the mean and variance of the 16 4 × 4 sub blocks of the MPEG-2 residual MBs. We use data mining algorithms to develop a decision tree for H.264 coding mode decisions. The decision trees are built using RD optimized mode decisions and result in highly efficient mode decisions, with significantly reduced computational complexity. The proposed transcoder is 35% faster than the RD optimized H.264 reference transcoder without a significant PSNR degradation (0.05 dB on average). The proposed transcoder performs over 0.4 dB better on average than the SAE cost based H.264 transcoding.

Recovering Connected Error Region Based on Adaptive Error Concealment Order Determination

Parts of compressed video streams may be lost or corrupted when being transmitted over bandwidth limited networks and wireless communication networks with error-prone channels. Error concealment (EC) techniques are often adopted at the decoder side to improve the quality of the reconstructed video. Under the conditions of a high rate of data packets that arrives at the decoder corrupted, it is likely that the incorrectly decoded macro-blocks (MBs) are concentrated in a connected region, where important spatial reference information is lost. The conventional EC methods usually carry out the block concealment following a lexicographic scan (from top to bottom and from left to right of the image), which would make the methods ineffective for the case that the corrupted blocks are grouped in a connected region. In this paper, a temporal error concealment method, adaptive error concealment order determination (AECOD), is proposed to recover connected corrupted regions. The processing order of an MB in a connected corrupted region is adaptively determined by analyzing the external boundary patterns of the MBs in its neighborhood. The performances, on several video sequences, of the proposed EC scheme have been compared with those obtained by using other error concealment methods reported in the literature. Experimental results show that the AECOD algorithm can improve the recovery performance with respect to the other considered EC methods.      

基于反馈的可伸缩视频编码容错策略

为提高可伸缩视频编码(SVC)在易错传输环境下的解码质量,研究帧内宏块刷新和参考帧选择2种容错技术,根据视频空间分层下SVC的层间预测特性,提出2种改进策略并进行对比。测试结果表明,在码率控制的情况下,改进的参考帧选择策略传输后重建图像的平均亮度峰值信噪比较高,更适用于低码率的传输环境。     

Efficient two-stage early SKIP mode termination for depth video coding

The video plus depth format has been widely-used in multi-view video systems. Therefore, low complexity depth video coding becomes very essential. For that, an efficient two-stage early SKIP mode termination (TESMT) algorithm is proposed in this paper. First, by using texture-depth correlation, our approach first checks whether current macroblock (MB) is motionless or slow-motion based on motion activity of corresponding region in texture video. If so, SKIP mode is selected as optimal mode and mode decision process is early terminated. Otherwise, our approach further checks whether the rate-distortion cost of SKIP mode is below an adaptive threshold, which is derived by exploiting spatial-temporal correlation between current MB and its adjacent MBs in depth video. Experimental results show that proposed algorithm significantly reduces computational complexity while keeping almost the same coding efficiency of depth video and quality of synthesized view, compared with exhaustive mode decision in multi-view video coding.     

Region-based error concealment of right-view frames for stereoscopic video transmission

Transmission of stereoscopic video stream through error-prone wireless channels results in the loss of blocks. In this paper, we propose a region-based error concealment method that exploits encoding modes, inter-view and intra-view correlations of stereoscopic video sequences. Based on the statistical analysis of the encoding modes of the surrounding macroblocks (MBs) and of the spatially corresponding MB in the neighboring frame, the lost MBs are classified into three types: (1) smooth MBs, (2) regular motion MBs and (3) irregular motion MBs. Following the classification, corresponding operations, including direct replacement, quarter-pixel motion and disparity compensation, and bilateral error concealment with adjustable weights, are applied to reconstruct the smooth MBs, regular motion MBs and irregular motion MBs, respectively. Experimental results show that the proposed method outperforms other existing error concealment methods for stereoscopic video transmission in terms of both objective and subjective evaluations.     

Error resilient video coding with priority data classification using H.264 flexible macroblock ordering

Flexible macroblock ordering (FMO) is a new error resilience feature in the H.264 (MPEG-4 part 10) video coding standard. The paper exploits FMO to offer a new classification algorithm for prioritised video transmission. Instead of using the default mapping structures of FMO, an optimisation algorithm in which the more important macroblocks (MBs) are categorised in a separate slice group (SG), which corresponds to high-priority packets for transmission, is proposed. The importance of each MB is determined based on its eventual influence on picture quality. This is assessed by considering the fact that the successful transmission of an MB not only enhances the quality of the associated pixels, but also improves the quality of its adjacent lost MBs by improving the efficiency of error concealment. It is assumed that the network can offer a prioritised service for successful transmission of the high-priority SG. Based on this, a vulnerability factor for each MB is determined, and a certain proportion of high-vulnerability MBs at each frame to limit the impact of temporal error propagation is intra-updated. It is shown, where the proposed mapping algorithm outperforms the default mappings of the H.264 codec, that this prioritised transmission will improve the subjective and objective video quality in situations with a high probability of transmission errors.     

高效的I帧分区错误隐藏方法

针对现有I帧错误隐藏方法不能平衡恢复图像质量与算法复杂度的问题,提出了一种高效的I帧分区错误隐藏方法。首先,利用视频帧之间的运动相关性将丢失宏块分为运动宏块和静止宏块。对于静止宏块,采用帧拷贝法进行掩盖;对于运动宏块,再根据其周围正确解码宏块的纹理信息将其分为平滑块和纹理块。对平滑块采用双线性插值法进行恢复;对纹理块利用比较精细的指数分布权重的加权模板匹配(WTE)法进行掩盖。实验结果表明,与WTE算法相比,所提方法的峰值信噪比(PSNR)平均提高了2.6 dB,计算复杂度平均降低了90%。对于场景连续的具有不同特征和分辨率的视频序列,所提方法都具有一定的适用性。     

基于DCT系数的自适应误码掩盖算法

提出一种改进的误码掩盖算法,即自适应地选择加权插值和区域匹配方法恢复丢失块.不同于以往只利用平滑性的误码掩盖算法,该算法利用平滑信息和纹理信息,在可用的相邻宏块中基于DCT系数计算能量函数总和,自动分析图像的平滑性和纹理性,然后自适应地选择加权插值或区域匹配的结果恢复丢失块.该算法已在H.264的参考软件JM86上进行实验.实验结果表明,与H.264中只采用加权插值或只采用区域匹配相比,该算法能取得较好的峰值信噪比(PSNR)和主观质量.     

一种改进的H.264 Intra 4×4帧内预测算法

H.264帧内编码通过空间预测减小变换编码输入值的大小,提高编码压缩性能。由于块编码总按照从左往右和从上往下的顺序,帧内预测可选的参考像素限制于块的左边和上边,因此预测结果不理想。该文提出一种基于宏块内部灵活的子块编码顺序的Intra 4×4预测编码算法,自适应地选择最佳预测参考像素集,同时对空间预测模式进行了改进。通过有限的子块分组和子块顺序选择,可以实现宏块内部编码最优化。仿真试验表明,和H.264相比,该算法可以取得平均0.4 dB 的PSNR编码性能增益。     

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。     

Fast mode selection for H.264 video coding standard based on motion region classification

H.264/AVC achieves higher compression efficiency than previous video coding standards. However, the process of selecting the optimal coding mode for each macroblock (MB) results in extremely high computation complexity, which make it difficult for practical use. In this paper, an efficient algorithm is proposed to reduce the complexity of MB mode selection. The proposed algorithm identified the interior region of the motion object by using the motion vectors information firstly. For the interior region surrounded by the identical motion vectors, we skip the mode selection of the MBs and then treat them with large block size modes directly. We also discuss the specific examples in this region. For the boundary region, we classify them into different types according to the coded mode information. After that we process the different regions with different mode set distinctly. Experimental results show that the proposed algorithm can save the encoding time up to 46% on average compared to the conventional method in the JVT JM8.6 reference encoder with only 0.12 dB performance degradation.     

一种基于H.264的混合视频转码方法*

为了提高比特率缩减的H.264视频转码速度,提出了一种混合型视频转码（mixtue video transcode,MVT）方法。该方法选择串联结构对intra帧进行转换编码,选择开环结构对inter帧进行转换编码,同时对inter帧进行部分误差消除操作。对intra帧,转换编码操作后可以得到无误差的intra帧;对于inter帧,转码后图像质量的损失大于串联结构,但因为进行了消除误差漂移的操作,这一损失可以控制在可接受的最小范围内。实验结果表明,提出的混合型视频转码结构在转码速度上远远高于串联结构,转