Total Encoding Time Reduction Research Articles

Latitude-Redundancy-Aware All-Zero Block Detection for Fast 360-Degree Video Coding.

The sphere-to-plane projection of 360-degree video introduces substantial stretched redundant data, which is discarded when reprojected to the 3D sphere for display. Consequently, encoding and transmitting such redundant data is unnecessary. Highly redundant blocks can be referred to as all-zero blocks (AZBs). Detecting these AZBs in advance can reduce computational and transmission resource consumption. However, this cannot be achieved by existing AZB detection techniques due to the unawareness of the stretching redundancy. In this paper, we first derive a latitude-adaptive redundancy detection (LARD) approach to adaptively detect coefficients carrying redundancy in transformed blocks by modeling the dependency between valid frequency range and the stretching degree based on spectrum analysis. Utilizing LARD, a latitude-redundancy-aware AZB detection scheme tailored for fast 360-degree video coding (LRAS) is proposed to accelerate the encoding process. LRAS consists of three sequential stages: latitude-adaptive AZB (L-AZB) detection, latitude-adaptive genuine-AZB (LG-AZB) detection and latitude-adaptive pseudo-AZB (LP-AZB) detection. Specifically, L-AZB refers to the AZB introduced by projection. LARD is used to detect L-AZB directly. LG-AZB refers to the AZB after hard-decision quantization and zeroing redundant coefficients. A novel latitude-adaptive sum of absolute difference estimation model is built to derive the threshold for LG-AZB detection. LP-AZB refers to the AZB in terms of rate-distortion optimization considering redundancy. A latitude-adaptive rate-distortion model is established for LP-AZB detection. Experimental results show that LRAS can achieve an average total encoding time reduction of 25.85% and 20.38% under low-delay and random access configurations compared to the original HEVC encoder, with only 0.16% and 0.13% BDBR increases and 0.01dB BDPSNR loss, respectively. The transform and quantization time savings are 60.13% and 59.94% on average.

An Adjacency Encoding Information-Based Fast Affine Motion Estimation Method for Versatile Video Coding

Versatile video coding (VVC), a new generation video coding standard, achieves significant improvements over high efficiency video coding (HEVC) due to its added advanced coding tools. Despite the fact that affine motion estimation adopted in VVC takes into account the translational, rotational, and scaling motions of the object to improve the accuracy of interprediction, this technique adds a high computational complexity, making VVC unsuitable for use in real-time applications. To address this issue, an adjacency encoding information-based fast affine motion estimation method for VVC is proposed in this paper. First, this paper counts the probability of using the affine mode in interprediction. Then we analyze the trade-off between computational complexity and performance improvement based on statistical information. Finally, by exploring the mutual exclusivity between skip and affine modes, an enhanced method is proposed to reduce interprediction complexity. Experimental results show that compared with the VVC, the proposed low-complexity method achieves 10.11% total encoding time reduction and 40.85% time saving of affine motion estimation with a 0.16% Bjøontegaard delta bitrate (BDBR) increase.

A computationally scalable fast intra coding scheme for HEVC video encoder

The High Efficiency Video Coding (HEVC) adopts 35 intra prediction modes to provide a more precise intra prediction. As a result, HEVC intra coding is much more complex. To provide a flexible solution for battery-powered devices, which include varying power budgets based on battery level, this paper jointly employs statistical distribution of different intra modes, and texture analysis. While the statistical information specifies the most efficient modes for extremely low power budgets, for moderate to high power budgets the best angular modes are predicted by analyzing the residual of the Planar mode, which is demonstrated to represent the dominant edges of the block. Moreover, a scheme is presented that further reduces the complexity by predicting the more important DC and Planar modes using the information provided by the entropy coder. The proposed method imposes almost no computational overhead since it utilizes the existing internal operators of HEVC. Ultimately, an intra prediction scheme with seven predefined levels of complexity is presented that provides coding for various power budgets and devices with various capabilities. The highest level of this scheme provides ~23% total encoding time reduction compared to HM, in all-intra configuration, with only 0.78% penalty on BD-Rate for high end devices. While the lowest level makes encoding possible for extremely low power devices and low battery plans with ~52% time reduction (almost the entire share of intra coding) at the cost of 9.6% BD-Rate, which is shown to be nearly minimal for this level of processing power.

Hybrid Laplace Distribution-Based Low Complexity Rate-Distortion Optimized Quantization.

Rate distortion optimized quantization (RDOQ) is an efficient encoder optimization method that plays an important role in improving the rate-distortion (RD) performance of the high-efficiency video coding (HEVC) codecs. However, the superior performance of RDOQ is achieved at the expense of high computational complexity cost in two stages RD minimization, including the determination of optimal quantized level among available candidates for each transformed coefficient and the determination of best quantized coefficients for transform units with the minimum total cost, to softly optimize the quantized coefficients. To reduce the computational cost of the RDOQ algorithm in HEVC, we propose a low-complexity RDOQ scheme by modeling the statistics of the transform coefficients with hybrid Laplace distribution. In this manner, specifically designed block level rate and distortion models are established based on the coefficient distribution. Therefore, the optimal quantization levels can be directly determined by optimizing the RD performance of the whole block, while the complicated RD cost calculations can be eventually avoided. Extensive experimental results show that with about 0.3%-0.4% RD performance degradation, the proposed low-complexity RDOQ algorithm is able to reduce around 70% quantization time with up to 17% total encoding time reduction compared with the original RDOQ implementation in HEVC on average.

Fast intra encoding decisions for high efficiency video coding standard

The high efficiency video coding standard (HEVC) is the next-generation standard developed by the Joint Collaborative Team in Video Coding (JCT-VC). This new standard aims to achieve 50 % bit rate saving with similar objective quality compared to H.264/AVC. A very flexible quadtree coding structure characterized by coding units (CUs), prediction units (PUs) and transform unit (TUs) is adopted by HEVC. However, this structure also introduces great computational complexity on the decision of optimal CU, PU and TU modes. To reduce the intra encoding complexity, we propose a solution which includes fast CU skip decision, fast CU early termination, fast PU mode decision and fast TU size decision. Experimental results demonstrate that the proposed solution achieves on average 65 % total encoding time reduction with less than 1.3 % average BD rate increase.

Efficient Multi-Reference Frame Selection Algorithm for Hierarchical B Pictures in Multiview Video Coding

Multiple reference frame prediction technology is adopted in Multiview Video Coding (MVC) to explore temporal and inter-view redundancies of multiview videos, resulting in extremely high encoding complexity by searching the best reference frame indices and the best reference directions for each macroblock (MB). In order to reduce MVC coding computations while keeping the coding efficiency and thus to advance MVC in real-time multimedia broadcasting applications, we propose a Fast Multi-reference Frame Selection Algorithm (FMFSA) for hierarchical B picture prediction structure in this paper. Due to high spatial correlations within a MB, there is a high probability for smaller MB partition modes selecting the same reference frame and direction as B16 16 does. Therefore, the reference information of latter checked MB partition modes can be directly set according to the reference information of previous examined mode. Experimental results on MVC show that the proposed FMFSA can achieve 68.34%~79.01% total encoding time reduction while the average bit rate increase and peak signal-to-noise ratio degradation are within 0.54% and 0.04 dB, respectively for test multiview sequences with various motion properties and camera arrangements.

Multi-direction search algorithm for block motion estimation in H.264/AVC

Many efficient search algorithms such as three-step search, new three-step search, four-step search, block-based gradient descent search, diamond search and hexagon-based search are developed for block motion estimation (ME) to search for the optimal objective function. The block ME technique involves an optimisation problem. Although these algorithms can converge to a minimal point rapidly, they suffer from becoming trapped in local minimum if the objective function has multiple minima. To solve this problem, the hybrid multi-hexagon-grid search (UMHexagonS) algorithm has been proposed in H.264/AVC, in which an unsymmetrical-cross search and an uneven UMHexagonS are employed over a wide search range to find a nearly global minimum. The experiment shows that the hybrid UMHexagonS algorithm is computation expensive and is occasionally trapped in local minimum. The authors propose a novel and fast search algorithm, called multi-direction search (MDS) algorithm, which uses an MDS first to find all possible locally optimal points and then uses the extended hexagon search to refine these points for the final optimal motion vector. The experimental results indicate that a significant improvement in computation reduction (∼30 and 50% reduction in average search points, corresponding to 19 and 37% reduction in total encoding time, for MDS and fast MDS, respectively) can be achieved while maintaining better coding performance, compared with the hybrid UMHexagonS algorithm.

Fast Inter-Mode Decision in an H.264/AVC Encoder Using Mode and Lagrangian Cost Correlation

In this paper we present a novel algorithm to speed up the inter-mode decision process for the H.264/AVC encoding. The proposed inter-mode decision scheme determines the best coding mode of a given macroblock (MB) by predicting the best mode from neighboring MBs in time and in space and by estimating its rate-distortion (RD) cost from the MB in the previous frame. The performance of the proposed algorithm is evaluated in metrics such as the encoding time, the average peak signal-to-noise ratio and the coding bit-rate for test sequences. Simulation results demonstrate that the proposed algorithm can determine the best mode using only one or two rate-distortion cost computations for about half of the MBs resulting in up to 56% total encoding time reduction with on average 2.4% of bit rate increase at the same PSNR compared to H.264/AVC JM 12.1.

다시점 영상 부호화에서 전역 변이 벡터를 이용한 고속 모드 결정

Multi-view video coding (MVC) based on H.264/AVC encodes multiple views efficiently by using a prediction scheme that exploits inter-view correlation among multiple views. However, with the increase of the number of views and use of inter-view prediction among views, total encoding time will be increased in multiview video coding. In this paper, we propose a fast mode decision using both MB(Macroblock)-based region segmentation information corresponding to each view in multiple views and global disparity vector among views in order to reduce encoding time. The proposed method achieves on average 40% reduction of total encoding time with the objective video quality degradation of about 0.04 dB peak signal-to-noise ratio (PSNR) by using joint multi-view video model (JMVM) 4.0 that is the reference software of the multiview video coding standard.