Enhanced Inter Mode Decision Based on Contextual Prediction for P‐Slices in H.264/AVC Video Coding

We propose a fast macroblock mode prediction and decision algorithm based on contextual information for P‐slices in the H.264/AVC video standard, in which the mode prediction part is composed of intra and inter modes. There are nine 4×4 and four 16×16 modes in the intra mode prediction, and seven block types exist for the best coding gain based on rate‐distortion optimization. This scheme gives rise to exhaustive computations (search) in the coding procedure. To overcome this problem, a fast inter mode prediction scheme is applied that uses contextual mode information for P‐slices. We verify the performance of the proposed scheme through a comparative analysis of experimental results. The suggested mode search procedure increased more than 57% in speed compared to a full mode search and more than 20% compared to the other methods.     

Fast Inter Mode Decision Algorithm Based on Macroblock Tracking in H.264/AVC Video

We propose a fast macroblock (MB) mode prediction and decision algorithm based on temporal correlation for P‐slices in the H.264/AVC video standard. There are eight block types for temporal decorrelation, including SKIP mode based on rate‐distortion (RD) optimization. This scheme gives rise to exhaustive computations (search) in the coding procedure. To overcome this problem, a thresholding method for fast inter mode decision using a MB tracking scheme to find the most correlated block and RD cost of the correlated block is suggested for early stop of the inter mode determination. We propose a two‐step inter mode candidate selection method using statistical analysis. In the first step, a mode is selected based on the mode information of the co‐located MB from the previous frame. Then, an adaptive thresholding scheme is applied using the RD cost of the most correlated MB. Secondly, additional candidate modes are considered to determine the best mode of the initial candidate modes that does not satisfy the designed thresholding rule. Comparative analysis shows that a speed‐up factor of up to 70.59% is obtained when compared with the full mode search method with a negligible bit increment and a minimal loss of image quality.     

General Architecture for MPEG-2/H.263/H.264/AVC to H.264/AVC Intra Frame Transcoding

The latest international video-coding standard H.264/AVC significantly achieves better coding performance compared to prior video coding standards such as MPEG-2 and H.263, which have been widely used in today’s digital video applications. To provide the interoperability between different coding standards, this paper proposes an efficient architecture for MPEG-2/H.263/H.264/AVC to H.264/AVC intra frame transcoding, using the original information such as discrete cosine transform (DCT) coefficients and coded mode type. Low-frequency components of DCT coefficients and a novel rate distortion cost function are used to select a set of candidate modes for rate distortion optimization (RDO) decision. For H.263 and H.264/AVC, a mode refinement scheme is utilized to eliminate unlikely modes before RDO mode decision, based on coded mode information. The experimental results, conducted on JM12.2 with fast C8MB mode decision, reveal that average 58%, 59% and 60% of computation (re-encoding) time can be saved for MPEG-2, H.263, H.264/AVC to H.264/AVC intra frame transcodings respectively, while preserving good coding performance when compared with complex cascaded pixel domain transcoding (CCPDT); or average 88% (a speed up factor of 8) when compared with CCPDT without considering fast C8MB. The proposed algorithm for H.264/AVC homogeneous transcoding is also compared to the simple cascaded pixel domain transcoding (with original mode reuse). The results of this comparison indicate that the proposed algorithm significantly outperforms the mode reuse algorithm in coding performance, with only slightly higher computation.     

基于块参考像素特征的快速帧内预测模式选择新算法

帧内预测是H.264采用的一种编码新技术。与以前的编码标准相比,H.264编码性能有了很大的提高,但同时编码复杂度和计算量也明显增加。该文研究了提高H.264编码速度的途径,着重分析了帧内预测模式快速选择的问题。经过分析发现,4×4亮度块的参考像素亮度值通常具有相似性,对应地,4×4亮度块的9种预测模式所得的预测结果也是相近的。根据4×4亮度块参考像素的这一特征,该文提出了一种基于4×4亮度块参考像素特征的快速帧内预测模式选择算法。实验结果说明了该文算法的有效性,与H.264编码器JM92相比,该算法的计算量减少了46%,而编码质量、PSNR和输出码率保持基本不变。     

低复杂度的多视点视频编码宏块模式决策算法

为了降低多视点视频编码(MVC)的计算复杂度,提出了一种基于全局-局部率失真代价的低复杂度宏块模式决策算法。首先根据宏块候选模式的块尺寸和率失真代价特点,将所有候选模式分为大尺寸模式(Skip/Direct、Inter16×16和Intra16×16)和小尺寸模式(Inter16×8、Inter8×16、Inter8×8、Intra8×8和Intra4×4);接着统计已编码帧中这两类宏块模式的平均率失真代价,并利用这些平均率失真代价计算当前帧宏块模式决策的全局率失真代价;最后利用得到的全局率失真代价,并结合当前宏块已估计模式的局部率失真代价和空间邻近宏块的模式信息提前终止模式决策,具体包括对大尺寸宏块模式进行提前判定以及对小尺寸候选模式进行逐级选择。实验结果表明:与MVC参考代码中的全搜索模式决策算法相比,本文算法在时域预测视点和视点域预测视点上分别节省了74%和82%的平均编码时间,同时保持了良好的编码率失真性能;与现有模式决策快速算法相比,本文算法降低了更多的编码时间,并具有更好的编码率失真性能。     

Fast block mode decision algorithm in H.264/AVC video coding

The recent video coding standard H.264/AVC show extremely higher coding efficiency compare to any other previous standards. H.264/AVC can achieve over 50% of bit rate saving with same quality using the rate–distortion process, but it brings high computational complexity. In this paper, we propose an algorithm that can reduce the complexity of the codec by reducing the block mode decision process adaptively. Block mode decision process in H.264/AVC consists of inter mode decision process and intra mode decision process. We deal with reduction method for inter and intra mode decision. In this paper an efficient method is proposed to reduce the inter mode decision complexity using the direct prediction methods based on block correlation and adaptive rate distortion cost threshold for early stopping. The fast intra mode reduction algorithm based on inter mode information is also proposed to reduce the computational complexity. The experimental results show that the proposed algorithm can achieve up to 63.34–77.39% speed up ratio with a little PSNR loss. Increment in bit requirement is also not much noticeable.     

Efficient intra-mode skip algorithm using RD costs of SUB8 3 8 and I4MB

H.264/AVC employs a rate-distortion (RD) optimisation technique to determine the best coding mode for each macroblock (MB). An intra-mode skip decision algorithm is presented based on RD costs of the SUB8 times 8 mode and the 14 MB mode to reduce the processing time. Experimental results on test video sequences show that the computational complexity has been reduced by about 20%, with nearly negligible loss of peak signal-to-noise ratio (PSNR) value.     

Implicit Line-Based Intra 16×16 Prediction for H.264/AVC High-Quality Video Coding

In this paper, we propose an implicit line-based linear intra 16×16 prediction method for high-quality video coding. Typically, in H.264/AVC intra 16×16 vertical and horizontal prediction modes, 256 pixels in the current macroblock are predicted using 16 adjacent boundary pixels of reconstructed neighboring macroblocks. One problem of such a block-based intra prediction is that the prediction error increases as the distance between the reference and current pixels increases. Thus, the prediction accuracy of intra 16×16 vertical and horizontal modes is not sufficient for the mode decision stage. To ensure that the pixels are close to their predictor, we propose a new implicit intra prediction scheme, which makes full use of the correlation between lines instead of blocks. In the proposed method, we perform prediction, transformation, quantization, and reconstruction using the line-of-pixels (LOP) to improve the prediction accuracy. Experimental results show that the proposed algorithm provides an approximately 6.42?% bit-rate reduction compared to the H.264/AVC FRExt high profile, while maintaining the same decoding quality.     

Intra‐Mixture Prediction Mode and Enhanced Most Probable Mode Estimation for Intra Coding

We present intra‐mixture prediction (IMP) mode for intra prediction and an enhanced estimation method for most probable mode (MPM). IMP mode supports more flexibility in intra prediction by mixing 4…4 blocks and 8…8 blocks in one macroblock, while the enhanced MPM estimation extends the number of referenced neighboring blocks and efficiently uses their prediction modes depending on their positions. Simulation results show that the combination of both proposed methods provides a bit reduction in the Bjøntegaard delta bitrate by an average of 2.56% compared to H.264/AVC.     

Error Concealment Using Intra‐Mode Information Included in H.264/AVC‐Coded Bitstream

The H.264/AVC standard has adopted new coding tools such as intra‐prediction, variable block size, motion estimation with quarter‐pixel‐accuracy, loop filter, and so on. The adoption of these tools enables an H.264/AVC‐coded bitstream to have more information than was possible with previous standards. In this paper, we propose an effective spatial error concealment method with low complexity in H.264/AVC intra‐frame. From information included in an H.264/AVC‐coded bitstream, we use prediction modes of intra‐blocks to recover a damaged block. This is because the prediction direction in each prediction mode is highly correlated to the edge direction. We first estimate the edge direction of a damaged block using the prediction modes of the intra‐blocks adjacent to a damaged block and classify the area inside the damaged block into edge and flat areas. Our method then recovers pixel values in the edge area using edge‐directed interpolation, and recovers pixel values in the flat area using weighted interpolation. Simulation results show that the proposed method yields better video quality than conventional approaches.     

Fast macroblock encoding algorithm based on rate-distortion activity for multiview video coding

Multiview video coding (MVC) is the appendix H of H.264/AVC, and it requires a great amount of time to compress multiple viewpoints׳ video with complex prediction structures. To reduce the whole computational complexity of MVC, this paper proposes a fast macroblock (MB) encoding algorithm based on rate-distortion (RD) activity, and it includes the fast mode decision and the fast motion/disparity estimation. First, the RD activity type of the current MB is calculated by utilizing the Skip/Direct RD cost and the average RD costs of classified MB modes. Then, through utilizing the RD activity type and RD costs of the estimated modes, the selection of candidate modes, the early decision of Skip/Direct mode, and the reduction of Inter8×8 mode estimation are all presented in the fast mode decision. By using the RD activity type and the correlations of vectors, the selection of search center and the prediction of search range are introduced in the fast motion/disparity estimation. In addition, the proposed algorithm can be applied to temporal and inter-view views as well as anchor and non-anchor frames. An experiment with a wide range of video scenes, camera setups and quantization parameters was implemented, and the results confirmed that the proposed algorithm can reduce the encoding time significantly while maintaining a similar RD performance as the original MVC encoder. Compared to the state-of-the-art algorithms, the proposed algorithm also demonstrated better performances in the various test cases.     

Gravity direction-based ultra-fast intraprediction algorithm for H.264/AVC video coding

The H.264/AVC video coding standard uses in intraprediction, 9 directional modes for 4 × 4 and 8 × 8 luma blocks, and 4 directional modes for 16 × 16 luma macroblocks, and 8 × 8 chroma blocks. The use of the variable block size and multiple modes in intraprediction makes the intracoding of H.264/AVC very efficient compared with other compression standards; however, computational complexity is increased significantly. In this paper, we propose a fast mode selection algorithm for intracoding. This algorithm is based on the vector of the block’s gravity center whose direction is used to select the best candidate prediction mode for intracoding. On this basis, only a small number of intraprediction modes are chosen for rate distortion optimization (RDO) calculation. Different video sequences are used to test the performance of proposed method. The simulation results show that the proposed algorithm increases significantly the speed of intracoding with negligible loss of peak signal-to-noise ratio quality.     

Selective VS-MRF-ME and intra coding in H.264 based on spatiotemporal continuity of motion field

The new video coding standard, H.264 uses variable size motion estimation (VS-ME), multiple reference frame motion estimation (MRF-ME) and spatial-based intra prediction with selectable block size in inter frame coding. These tools have achieved significant coding efficiency compared to coding a macroblock (MB) only based on motion-compensation in regular size with single reference frame. However, these new features also give rise to an exhaustive computation in the coding procedure since there are so many combinations of coding modes and reference frames to be tried. In this paper, a fast motion estimation algorithm based on the selective VS-MRF-ME and intra prediction is proposed to reduce H.264 coding computational complexity. The basic idea of the method is to utilize the spatiotemporal property of motion field in predicting where VS-MRF-ME and intra prediction are needed, and only in these regions VS-MRF-ME and intra coding are enabled. The motion field is generated by motion vectors from 16×16 motion estimation on the nearest reference frame. Simulation results show that the proposed algorithm can save 50% computational complexity on average, with negligible loss of coding efficiency.     

Efficient Mode Decision Algorithm Based on Spatial,Temporal, and Inter‐layer Rate‐Distortion Correlation Coefficients for Scalable Video Coding

The layered coding structure of scalable video coding (SVC) with adaptive inter‐layer prediction causes noticeable computational complexity increments when compared to existing video coding standards. To lighten the computational complexity of SVC, we present a fast algorithm to speed up the inter‐mode decision process. The proposed algorithm terminates inter‐mode decision early in the enhancement layers by estimating the rate‐distortion (RD) cost from the macroblocks of the base layer and the enhancement layer in temporal, spatial, and inter‐layer directions. Moreover, a search range decision algorithm is also proposed in this paper to further increase the motion estimation speed by using the motion vector information from temporal, spatial, or inter‐layer domains. Simulation results show that the proposed algorithm can determine the best mode and provide more efficient total coding time saving with very slight RD performance degradation for spatial and quality scalabilities.     

Enhanced SATD-based cost function for mode selection of H.264/AVC intra coding

In H.264/AVC, the concept of rate-distortion optimization (RDO) mode decision has proven to be an important coding tool. However, this mode decision method makes the encoding process extremely complex, especially in the computation of the rate-distortion cost function, which includes the computations of the sum of squared difference (SSD) between the original and reconstructed image blocks and context-based entropy coding of the block. In this paper, we propose an enhanced low-complexity cost function for H.264/AVC intra 4 × 4 and 8 × 8 mode selections. The enhanced cost function uses sum of absolute Hadamard-transformed differences (SATD) and mean absolute deviation of the residual block to estimate distortion part of the cost function. A threshold-based large coefficients count is also used for estimating the bit-rate part. The proposed method improves the rate-distortion performance of conventional fast cost functions while maintaining low complexity requirement. As a result, the encoding process can be significantly accelerated with the use of the proposed cost function. Simulation results confirm that the proposed method reduces about 83.74 % computation of intra encoding of JM 12.4 encoder with negligible rate-distortion performance degradation.     

CU encoding depth prediction,early CU splitting termination and fast mode decision for fast HEVC intra-coding

High Efficiency Video Coding (HEVC) is a new video coding standard achieving about a 50% bit rate reduction compared to the popular H.264/AVC High Profile with the same subjective reproduced video quality. Better coding efficiency is attained, however, at the cost of significantly increased encoding complexity. Therefore, fast encoding algorithms with little loss in coding efficiency is necessary for HEVC to be successfully adopted for real applications. In this paper we propose a fast encoding technique applicable to HEVC all intra encoding. The proposed fast encoding technique consists of coding unit (CU) search depth prediction, early CU splitting termination, and fast mode decision. In CU search depth prediction, the depth of encoded CU in the current coding tree unit (CTU) is limited to predicted range, which is mostly narrower than the full depth range. Early CU splitting skips mode search of its sub-CUs when rate distortion (RD) cost of current CU is below the estimated RD cost at the current CU depth. RD cost and encoded CU depth distribution of the collocated CTU of the previous frame are utilized both to predict the encoding CU depth search range and to estimate the RD cost for CU splitting termination. Fast mode decision reduces the number of candidate modes for full rate distortion optimized quantization on the basis of the low complexity costs computed in the preceding rough mode decision step. When all these three methods are applied, proposed fast HEVC intra encoding technique reduces the encoding time of the reference encoder by 57% on the average, with only 0.6% of coding efficiency loss in terms of Bjontegaard delta (BD) rate increase under the HEVC common test conditions.     

Fast transmission distortion estimation and adaptive error protection for H.264/AVC-based embedded video conferencing systems

This paper presents the design and implementation of an error-resilient H.264/AVC-based embedded video conferencing scheme over Internet. We first develop a fast recursive algorithm to estimate the decoder-side distortion of each frame in the presence of packet loss. The algorithm operates at block level, and considers the impacts of different intra prediction modes, the unrestricted intra prediction, and the skip mode. We then design a family of very short systematic forward error correction codes with linear encoding and decoding complexity, which runs across the slices of each frame to recover lost packets. An optimization problem is then formulated to minimize the decoder-side distortion by allocating a given channel coding redundancy among a group of frames. Various techniques are introduced to speed up the algorithm without sacrificing too much accuracy, in order to meet the hardware and real-time constraints of the system. As a result, the proposed scheme can run on a real-time embedded video conferencing system with resolution up to 1024×576 pixels, 30 frames per second (fps) and 4 megabits per second (Mbps).     

基于空间相关性的H.264快速自适应模式选择算法

为了减小H.264编码器的复杂度,提出了一种帧间预测模式快速自适应选择算法。该算法首先利用运动补偿后残差宏块的统计信息,将需要计算率失真代价函数的候选模式减少为一个模式组中包含的模式子集;然后根据相邻的左块和上块的模式,从所选择的模式子集中选出出现概率最高的两种模式来计算并比较率失真代价函数,选出代价最小的模式作为最佳模式。实验表明,本算法平均可以节省编码时间约65%,同时PSNR下降约为?0.24dB,有利于实时应用。     

一种H.264/AVC帧内预测模式的快速选择算法

H.264/AVC帧内预测技术采用率失真优化策略进行最优化编码模式选择,提高了I帧的编码效率,但同时也提高了计算复杂度。本文提出了一种帧内预测模式的快速选择算法,基于亮度块的方向特性,通过一些复杂度不大的计算,选择少数几个可能性较大的预测模式进行率失真代价计算,得到最佳亮度预测模式,并以 计算代替率失真代价计算选择最佳色度预测模式,降低了计算复杂度,提高了编码速度。实验结果表明,本文提出的算法在保证图像质量的同时,编码时间平均降低了48%,而码率增加很小。