Arild Fuldseth

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.

HEVC Deblocking Filter

This paper describes the in-loop deblocking filter used in the upcoming High Efficiency Video Coding (HEVC) standard to reduce visible artifacts at block boundaries. The deblocking filter performs detection of the artifacts at the coded block boundaries and attenuates them by applying a selected filter. Compared to the H.264/AVC deblocking filter, the HEVC deblocking filter has lower computational complexity and better parallel processing capabilities while still achieving significant reduction of the visual artifacts.

Core Transform Design in the High Efficiency Video Coding (HEVC) Standard

This paper describes the core transforms specified for the high efficiency video coding (HEVC) standard. Core transform matrices of various sizes from 4 × 4 to 32 × 32 were designed as finite precision approximations to the discrete cosine transform (DCT). Also, special care was taken to allow implementation friendliness, including limited bit depth, preservation of symmetry properties, embedded structure and basis vectors having almost equal norm. The transform design has the following properties: 16 bit data representation before and after each transform stage (independent of the internal bit depth), 16 bit multipliers for all internal multiplications, no need for correction of different norms of basis vectors during quantization/de-quantization, all transform sizes above 4 × 4 can reuse arithmetic operations for smaller transform sizes, and implementations using either pure matrix multiplication or a combination of matrix multiplication and butterfly structures are possible. The transform design is friendly to parallel processing and can be efficiently implemented in software on SIMD processors and in hardware for high throughput processing.

An Overview of Tiles in HEVC

Tiles is a new feature in the High Efficiency Video Coding (HEVC) standard that divides a picture into independent, rectangular regions. This division provides a number of advantages. Specifically, it increases the “parallel friendliness” of the new standard by enabling improved coding efficiency for parallel architectures, as compared to previous sliced based methods. Additionally, tiles facilitate improved maximum transmission unit (MTU) size matching, reduced line buffer memory, and additional region-of-interest functionality. In this paper, we introduce the tiles feature and survey the performance of the tool. Coding efficiency is reported for different parallelization factors and MTU size requirements. Additionally, a tile-based region of interest coding method is developed.

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 MPEG and VCEG, and has been partially adopted into the initial HEVC Test Model under Consideration design. The proposal utilizes a quad-tree structure with a support of large macroblocks of size 64×64 and 32×32, in addition to macroblocks of size 16×16. The entropy coding is done using a low complexity variable length coding based scheme with improved context adaptation over the H.264/AVC design. In addition, the proposal includes improved interpolation and deblocking filters, giving better coding efficiency while having low complexity. Finally, an improved intra coding method is presented. The subjective quality of the proposal is evaluated extensively and the results show that the proposed method achieves similar visual quality as H.264/AVC High Profile anchors with around 50% and 35% bit rate reduction for low delay and random-access experiments respectively at high definition sequences. This is achieved with less complexity than H.264/AVC Baseline Profile, making the proposal especially suitable for resource constrained environments.

HEVC Transform and Quantization

This chapter provides an overview of the transform and quantization design in HEVC. HEVC specifies two-dimensional transforms of various sizes from 4 × 4 to 32 × 32 that are finite precision approximations to the discrete cosine transform (DCT). In addition, HEVC also specifies an alternate 4 × 4 integer transform based on the discrete sine transform (DST) for use with 4 × 4 luma Intra prediction residual blocks. During the transform design, special care was taken to allow implementation friendliness, including limited bit depth, preservation of symmetry properties, embedded structure and basis vectors having almost equal norm. The HEVC quantizer design is similar to that of H.264/AVC where a quantization parameter (QP) in the range of 0–51 (for 8-bit video sequences) is mapped to a quantizer step size that doubles each time the QP value increases by 6. A key difference, however, is that the transform basis norm correction factors incorporated into the descaling matrices of H.264/AVC are no longer needed in HEVC simplifying the quantizer design. A QP value can be transmitted (in the form of delta QP) for a quantization group as small as 8 × 8 samples for rate control and perceptual quantization purposes. The QP predictor used for calculating the delta QP uses a combination of left, above and previous QP values. HEVC also supports frequency-dependent quantization by using quantization matrices for all transform block sizes. This chapter also provides an overview of the three special coding modes in HEVC (I_PCM mode, lossless mode, and transform skip mode) that modify the transform and quantization process by either skipping the transform or by skipping both transform and quantization.

Tiles for managing computational complexity of video encoding and decoding

In this paper, we introduce the concept of tiles. Tiles are incorporated into the current design of the High Efficiency Video Coding (HEVC) standard being developed by the Joint Collaborative Team on Video Coding (JCT-VC). In the design, tiles are introduced to support high-level parallelism and also to reduce on-chip memory requirements. This paper describes the tile concept and reports results due to the technique.

The Thor Video Codec

The Thor video codec is being developed by Cisco with the intention to use only royalty-free coding tools. The video codec is based on the well-known block-based hybrid video coding approach, but with some significant changes compared to existing standards such as AVC/H.264 and HEVC/H.265. These changes include transform coefficient coding, deblocking filter, a separate deringing filter, and interpolated reference frames. Experimental results show 14.5% and 15.3% BDR loss compared to the HEVC/H.265 reference software for low-delay and high-delay configurations respectively. When compared to optimized software implementations of VP9 and x265, Thor provides similar or better compression performance for the same frame rate.

HEVC deblocking filtering and decisions

The emerging High Efficiency Video Coding (HEVC) standard uses a block-based coding scheme, which may cause blocking artifacts, especially at lower bitrates. An adaptive in-loop deblocking filter is used in the standard to reduce visible artifacts at block boundaries. The deblocking filter detects artifacts at the block boundaries and attenuates them by applying a selected filter. This paper will present deblocking decisions and filtering operations that are used in HEVC.

Recent improvements to Thor with emphasis on perceptual coding tools

Thor supports a number of coding tools that have the potential to improve perceptual as well as objective quality. Synthetic reference frames may be used to support high frame rate applications in circumstances where encoders might typically transmit reduced frame rate content. Quantization matrices can be used to give improved visual quality by allocating bits more closely according to perceptual significance. Thor’s Constrained Low Pass Loop Filter provides significant subjective benefit in removing coding artefacts such as ringing. Improved colour fidelity can also be obtained by leveraging luma information. This paper discusses developments in these tools and their objective and subjective performance.