Antti Hallapuro

Low-complexity transform and quantization in H.264/AVC

This paper presents an overview of the transform and quantization designs in H.264. Unlike the popular 8/spl times/8 discrete cosine transform used in previous standards, the 4/spl times/4 transforms in H.264 can be computed exactly in integer arithmetic, thus avoiding inverse transform mismatch problems. The new transforms can also be computed without multiplications, just additions and shifts, in 16-bit arithmetic, thus minimizing computational complexity, especially for low-end processors. By using short tables, the new quantization formulas use multiplications but avoid divisions.

Comparative Rate-Distortion-Complexity Analysis of HEVC and AVC Video Codecs

This paper analyzes the rate-distortion-complexity of High Efficiency Video Coding (HEVC) reference video codec (HM) and compares the results with AVC reference codec (JM). The examined software codecs are HM 6.0 using Main Profile (MP) and JM 18.0 using High Profile (HiP). These codes are benchmarked under the all-intra (AI), random access (RA), low-delay B (LB), and low-delay P (LP) coding configurations. In order to obtain a fair comparison, JM HiP anchor codec has been configured to conform to HM MP settings and coding configurations. The rate-distortion comparisons rely on objective quality assessments, i.e., bit rate differences for equal PSNR. The complexities of HM and JM have been profiled at the cycle level with Intel VTune on Intel Core 2 Duo processor. The coding efficiency of HEVC is drastically better than that of AVC. According to our experiments, the average bit rate decrements of HM MP over JM HiP are 23%, 35%, 40%, and 35% under the AI, RA, LB, and LP configurations, respectively. However, HM achieves its coding gain with a realistic overhead in complexity. Our profiling results show that the average software complexity ratios of HM MP and JM HiP encoders are 3.2× in the AI case, 1.2× in the RA case, 1.5× in the LB case, and 1.3× in the LP case. The respective ratios with HM MP and JM HiP decoders are 2.0×, 1.6×, 1.5×, and 1.4×. This paper also reveals the bottlenecks of HM codec and provides implementation guidelines for future real-time HEVC codecs.

High Performance, Low Complexity Video Coding and the Emerging HEVC Standard

This paper describes a low complexity video codec with high coding efficiency. It was proposed to the high efficiency video coding (HEVC) standardization effort of moving picture experts group and video coding experts group, and has been partially adopted into the initial HEVC test model under consideration design. The proposal utilizes a quadtree-based coding structure with support for macroblocks of size 64 × 64, 32 × 32, and 16 × 16 pixels. Entropy coding is performed using a low complexity variable length coding scheme with improved context adaptation compared to the context adaptive variable length coding design in H.264/AVC. The proposals interpolation and deblocking filter designs improve coding efficiency, yet have low complexity. Finally, intra-picture coding methods have been improved to provide better subjective quality than H.264/AVC. The subjective quality of the proposed codec has been evaluated extensively within the HEVC project, with results indicating that similar visual quality to H.264/AVC High Profile anchors is achieved, measured by mean opinion score, using significantly fewer bits. Coding efficiency improvements are achieved with lower complexity than the H.264/AVC Baseline Profile, particularly suiting the proposal for high resolution, high quality applications in resource-constrained environments.

Complexity of optimized H.26L video decoder implementation

An analysis of computational complexity is presented for an H.26L video decoder, based on extensive experiments on a general-purpose processor. In addition, platform-independent techniques to optimize an H.26L decoder implementation are given. Comparisons are carried out between our highly optimized version of H.26L, the public reference implementation of H.26L, and a highly optimized H.263+ implementation. Both QCIF and CIF-sized image sequences are used. The results show that with equal visual quality, the bit-rate savings range from 28% to 58%, while the frame decoding speed of H.26L is about 11% better than that of a highly optimized H.263+.

Multiple Description Video Coding With H.264/AVC Redundant Pictures

Multiple description coding offers interesting solutions for error resilient multimedia communications as well as for distributed streaming applications. In this letter, we propose a scheme based on H.264/AVC for encoding of image sequences into multiple descriptions. The pictures are split into multiple coding threads. Redundant pictures are inserted periodically in order to increase the resilience to loss and to reduce the error propagation. They are produced with different reference frames than the corresponding primary pictures. We show, given the channel conditions, how to optimally allocate the rates to primary and redundant pictures, such that the total distortion at the receiver is minimized. Extensive experiments demonstrate that the proposed scheme outperforms baseline solutions based on loss and content-adaptive intra coding. Finally, we show how to further reduce the distortion by efficient combination of primary and redundant pictures, if both are available at the decoder.

Low-complexity transform and quantization with 16-bit arithmetic for H.26L

This paper presents an overview of the latest transform and quantization designs for H.26L. Unlike the popular discrete cosine transform (DCT) used in previous standards, the transforms in H.26L can be computed exactly in integer arithmetic, thus avoiding inverse transform mismatch problems. The new transforms can also be computed without multiplications, just additions and shifts, in 16-bit arithmetic, thus minimizing computational complexity, especially for low-end processors. By using short tables, the new quantization formulas use multiplications but avoid divisions.

Video Coding Using Spatially Varying Transform

In this paper, a novel algorithm called spatially varying transform (SVT) is proposed to improve the coding efficiency of video coders. SVT enables video coders to vary the position of the transform block, unlike state-of-art video codecs where the position of the transform block is fixed. In addition to changing the position of the transform block, the size of the transform can also be varied within the SVT framework, to better localize the prediction error so that the underlying correlations are better exploited. It is shown in this paper that by varying the position of the transform block and its size, characteristics of prediction error are better localized, and the coding efficiency is thus improved. The proposed algorithm is implemented and studied in the H.264/AVC framework. We show that the proposed algorithm achieves 5.85% bitrate reduction compared to H.264/AVC on average over a wide range of test set. Gains become more significant at medium to high bitrates for most tested sequences and the bitrate reduction may reach 13.50%, which makes the proposed algorithm very suitable for future video coding solutions focusing on high fidelity video applications. The gain in coding efficiency is achieved with a similar decoding complexity which makes the proposed algorithm easy to be incorporated in video codecs. However, the encoding complexity of SVT can be relatively high because of the need to perform a number of rate distortion optimization (RDO) steps to select the best location parameter (LP), which indicates the position of the transform. In this paper, a novel low complexity algorithm is also proposed, operating on a macroblock and a block level, to reduce the encoding complexity of SVT. Experimental results show that the proposed low complexity algorithm can reduce the number of LPs to be tested in RDO by about 80% with only a marginal penalty in the coding efficiency.

Performance analysis of low bit rate H.26L video encoder

A new video encoder proposal, H.26L, is compared against H.263 and H.263+. In the comparison, both computational complexity and compression performance are analyzed. Moreover, the trade-off possibilities between the complexity and compression performance within H.26L are presented. Experimental comparisons with H.263 and H.263+ show that H.26L reduces the output bit rate about 30% with the same quality. The computation time increases about three times compared to H.263 and leads into the encoding speed of 3-6 fps for QCIF sequences on a 400 MHz Pentium III processor. Realtime operation can be achieved by applying additional, algorithmic and platform-specific optimizations.

Video Coding With Low-Complexity Directional Adaptive Interpolation Filters

A novel adaptive interpolation filter structure for video coding with motion-compensated prediction is presented in this letter. The proposed scheme uses an independent directional adaptive interpolation filter for each sub-pixel location. The Wiener interpolation filter coefficients are computed analytically for each inter-coded frame at the encoder side and transmitted to the decoder. Experimental results show that the proposed method achieves up to 1.1 dB coding gain and a 15% average bit-rate reduction for high-resolution video materials compared to the standard nonadaptive interpolation scheme of H.264/AVC, while requiring 36% fewer arithmetic operations for interpolation. The proposed interpolation can be implemented in exactly 16-bit arithmetic, thus it can have important use-cases in mobile multimedia environments where the computational resources are severely constrained.

Multiple description h.264 video coding with redundant pictures

Multiple description coding (MDC) offers a competitive solutionfor video transmission over lossy packet networks,with a graceful degradation of the reproduced quality as theloss rate increases. This paper illustrates how redundantpictures, an error resilience tool included in H.264/AVC,can be employed in conjunction with multiple state videocoding scheme, previously proposed in the literature. Theproposed MDC solution is shown to provide superior performanceto state-of-the-art techniques, in terms of improvedaverage luma peak-signal-to-noise-ratio (PSNR), fewer temporalfluctuations in the picture quality, and improved robustnessto bad estimation of the loss probability in thenetwork.