Guilherme Corrêa

Performance and Computational Complexity Assessment of High-Efficiency Video Encoders

This paper presents a performance evaluation study of coding efficiency versus computational complexity for the forthcoming High Efficiency Video Coding (HEVC) standard. A thorough experimental investigation was carried out to identify the tools that most affect the encoding efficiency and computational complexity of the HEVC encoder. A set of 16 different encoding configurations was created to investigate the impact of each tool, varying the encoding parameter set and comparing the results with a baseline encoder. This paper shows that, even though the computational complexity increases monotonically from the baseline to the most complex configuration, the encoding efficiency saturates at some point. Moreover, the results of this paper provide relevant information for implementation of complexity-constrained encoders by taking into account the tradeoff between complexity and coding efficiency. It is shown that low-complexity encoding configurations, defined by careful selection of coding tools, achieve coding efficiency comparable to that of high-complexity configurations.

Complexity control of high efficiency video encoders for power-constrained devices

The emerging High Efficiency Video Coding (HEVC) standard is expected to require much more processing power than its predecessors due to the higher algorithmic complexity of new coding tools and associated data structures. This paper proposes a novel complexity control method for the near future HEVC encoders running on power-constrained devices. The proposed method is based on a decision algorithm that dynamically adjusts the depth of the Coding Units (CU) defined by quad-tree structures. New evidence about the relationship between CU depth and coding complexity is used to selectively constrain the CU depth in order to not exceed a predefined complexity target. The experimental results show that the encoder computational complexity can be downscaled by up to 60% at the cost of negligible loss of rate-distortion (RD) performance. The proposed method finds application in the near future multimedia portable devices using HEVC codecs.

Fast HEVC Encoding Decisions Using Data Mining

The High Efficiency Video Coding standard provides improved compression ratio in comparison with its predecessors at the cost of large increases in the encoding computational complexity. An important share of this increase is due to the new flexible partitioning structures, namely the coding trees, the prediction units, and the residual quadtrees, with the best configurations decided through an exhaustive rate-distortion optimization (RDO) process. In this paper, we propose a set of procedures for deciding whether the partition structure optimization algorithm should be terminated early or run to the end of an exhaustive search for the best configuration. The proposed schemes are based on decision trees obtained through data mining techniques. By extracting intermediate data, such as encoding variables from a training set of video sequences, three sets of decision trees are built and implemented to avoid running the RDO algorithm to its full extent. When separately implemented, these schemes achieve average computational complexity reductions (CCRs) of up to 50% at a negligible cost of 0.56% in terms of Bjontegaard Delta (BD) rate increase. When the schemes are jointly implemented, an average CCR of up to 65% is achieved, with a small BD-rate increase of 1.36%. Extensive experiments and comparisons with similar works demonstrate that the proposed early termination schemes achieve the best rate-distortion-complexity tradeoffs among all the compared works.

Coding Tree Depth Estimation for Complexity Reduction of HEVC

The emerging HEVC standard introduces a number of tools which increase compression efficiency in comparison to its predecessors at the cost of greater computational complexity. This paper proposes a complexity control method for HEVC encoders based on dynamic adjustment of the newly proposed coding tree structures. The method improves a previous solution by adopting a strategy that takes into consideration both spatial and temporal correlation in order to decide the maximum coding tree depth allowed for each coding tree block. Complexity control capability is increased in comparison to a previous work, while compression losses are decreased by 70%. Experimental results show that the encoder computational complexity can be downscaled to 60% with an average bit rate increase around 1.3% and a PSNR decrease under 0.07 dB.

Complexity scalability for real-time HEVC encoders

The high efficiency video coding (HEVC) standard achieves improved compression efficiency in comparison to previous standards at the cost of much higher computational complexity and consequently longer processing times, which may compromise real-time software-based video encoding, especially at high resolutions. This article addresses the problem of enabling complexity scalability in HEVC encoders by trading-off processing time for rate–distortion (R–D) performance in a controlled manner. The proposed method is based on dynamic constraining of HEVC coding treeblocks (CTBs) by limiting the prediction block (PB) shapes and the maximum tree depth used in each CTB, to decrease the number of R–D evaluations performed in the optimization process. The complexity-scalable encoder is capable of adjusting the processing time used in each group of pictures, according to a predefined target. The results show that processing times can be scaled down to 50xa0% with negligible R–D performance losses and down to 20xa0% at a maximum BD-PSNR decrease of 1.41xa0dB, which is acceptable in many applications and in power constrained devices. The simplicity of the scaling algorithm and the possibility of continuous adjustment of the scaling factor make it amenable to control real-time software-based HEVC video encoders.

Adaptive coding tree for complexity control of high efficiency video encoders

The emerging HEVC standard introduces several techniques which increase compression efficiency in comparison to its predecessors. However, such advances are accompanied by increases in computational complexity, limiting the encoder use in computational or power-constrained devices. This paper proposes a novel complexity control method for the future HEVC encoders based on a dynamic adjustment of the newly proposed coding tree structures. The relationship between coding tree depths and the encoding complexity is explored to selectively constrain encoding possibilities in order to not exceed a predefined complexity target. Experimental results show that the encoder computational complexity can be downscaled to 60% with a bit rate increase under 3.5% and a PSNR decrease under 0.1 dB.

Complexity control of HEVC through quadtree depth estimation

The emerging HEVC standard introduces a number of tools which increase compression efficiency in comparison to its predecessors at the cost of greater computational complexity. This paper proposes a complexity control method for HEVC encoders based on dynamic adjustment of the newly proposed coding tree structures. The method improves a previous solution by adopting a strategy that takes into consideration both spatial and temporal correlation in order to decide the maximum coding tree depth allowed for each coding tree block. Complexity control capability is increased in comparison to a previous work, while compression losses are decreased by 70%. Experimental results show that the encoder computational complexity can be downscaled to 60% with an average bit rate increase around 1.3% and a PSNR decrease under 0.07 dB.

Algorithm and hardware design of a fast intra-frame mode decision module for h.264/AVC encoders

In the Rate-Distortion Optimization (RDO) technique for video encoding, the process of choosing the best prediction mode is performed through exhaustive executions of the whole encoding process, which increases significantly the encoder computational complexity. Considering H.264/AVC intra-frame prediction there are several modes to encode each macroblock (MB). In order to reduce the number of calculations necessary to determine the best intra-frame mode, this work proposes an algorithm and the hardware design for a fast intra-frame mode decision module for H.264/AVC encoders. The application of the proposed algorithm reduces in more than ten times the number of encoding iterations for choosing the best intra-frame mode when compared with RDO-based decision, at the cost of relatively small bit-rate increase (5% in average) and image quality loss (0.2 dB in PSNR). The architecture takes 36 clock cycles to perform the intra-frame decision for one MB and it achieved an operation frequency of 130 MHz when synthesized for TSMC 0.18μm, being able to process more than 400 HD1080p frames per second. With this approach, we achieved one order-of-magnitude performance improvement compared with RDO-based approaches, which is very important not only from the performance but also from the energy consumption perspective when considering the need to improve the video encoding efficiency for battery operated devices. Compared with the best previous results reported, the implemented architecture achieve a complexity reduction of five times, a processing capability increase of 14 times and a reduction in the number of clock cycles per MB of 11 times.

Motion compensated tree depth limitation for complexity control of HEVC encoding

The recently introduced quadtree coding structures used in HEVC increase compression efficiency in comparison to previous standards at the cost of higher computational complexity levels. This paper proposes an evolution of a complexity control method for HEVC encoders based on the dynamic adjustment of these structures maximum depth. The new method improves the previous solution by adopting a new control strategy and compensating the motion effect on a maximum tree depth map which is central to the complexity control strategy. The proposed method is capable of performing a more accurate complexity control than our previous strategy while still reducing compression efficiency losses in terms of image quality and bit rate.

Encoding time control system for HEVC based on Rate-Distortion-Complexity analysis

The improved compression efficiency of High Efficiency Video Coding (HEVC) comes with large increases in computational complexity, which has been lately dealt by researchers with complexity reduction and scaling methods. However, encoding time control at frame or Group of Pictures (GOP) level is still an open issue that must be investigated. In this work, a Rate-Distortion-Complexity analysis is performed upon a set of configurations that have been created based on findings and techniques of previous works. The proposed control system uses the best 27 configurations to adjust the encoding time per GOP and yields encoding time reductions of up to 84.5% with an average difference between target and encoding times of 4.1%.