CAVLC Research Articles

CAVLCU: an efficient GPU-based implementation of CAVLC

CAVLC (Context-Adaptive Variable Length Coding) is a high-performance entropy method for video and image compression. It is the most commonly used entropy method in the video standard H.264. In recent years, several hardware accelerators for CAVLC have been designed. In contrast, high-performance software implementations of CAVLC (e.g., GPU-based) are scarce. A high-performance GPU-based implementation of CAVLC is desirable in several scenarios. On the one hand, it can be exploited as the entropy component in GPU-based H.264 encoders, which are a very suitable solution when GPU built-in H.264 hardware encoders lack certain necessary functionality, such as data encryption and information hiding. On the other hand, a GPU-based implementation of CAVLC can be reused in a wide variety of GPU-based compression systems for encoding images and videos in formats other than H.264, such as medical images. This is not possible with hardware implementations of CAVLC, as they are non-separable components of hardware H.264 encoders. In this paper, we present CAVLCU, an efficient implementation of CAVLC on GPU, which is based on four key ideas. First, we use only one kernel to avoid the long latency global memory accesses required to transmit intermediate results among different kernels, and the costly launches and terminations of additional kernels. Second, we apply an efficient synchronization mechanism for thread-blocks (In this paper, to prevent confusion, a block of pixels of a frame will be referred to as simply block and a GPU thread block as thread-block.) that process adjacent frame regions (in horizontal and vertical dimensions) to share results in global memory space. Third, we exploit fully the available global memory bandwidth by using vectorized loads to move directly the quantized transform coefficients to registers. Fourth, we use register tiling to implement the zigzag sorting, thus obtaining high instruction-level parallelism. An exhaustive experimental evaluation showed that our approach is between 2.5times and 5.4times faster than the only state-of-the-art GPU-based implementation of CAVLC.

Design and ARM-Based Implementation of Bitstream-Oriented Chaotic Encryption Scheme for H.264/AVC Video.

In actual application scenarios of the real-time video confidential communication, encrypted videos must meet three performance indicators: security, real-time, and format compatibility. To satisfy these requirements, an improved bitstream-oriented encryption (BOE) method based chaotic encryption for H.264/AVC video is proposed. Meanwhile, an ARM-embedded remote real-time video confidential communication system is built for experimental verification in this paper. Firstly, a 4-D self-synchronous chaotic stream cipher algorithm with cosine anti-controllers (4-D SCSCA-CAC) is designed to enhance the security. The algorithm solves the security loopholes of existing self-synchronous chaotic stream cipher algorithms applied to the actual video confidential communication, which can effectively resist the combinational effect of the chosen-ciphertext attack and the divide-and-conquer attack. Secondly, syntax elements of the H.264 bitstream are analyzed in real-time. Motion vector difference (MVD) coefficients and direct-current (DC) components in Residual syntax element are extracted through the Exponential-Golomb decoding operation and entropy decoding operation based on the context-based adaptive variable length coding (CAVLC) mode, respectively. Thirdly, the DC components and MVD coefficients are encrypted by the 4-D SCSCA-CAC, and the encrypted syntax elements are re-encoded to replace the syntax elements of the original H.264 bitstream, keeping the format compatibility. Besides, hardware codecs and multi-core multi-threading technology are employed to improve the real-time performance of the hardware system. Finally, experimental results show that the proposed scheme, with the advantage of high efficiency and flexibility, can fulfill the requirement of security, real-time, and format compatibility simultaneously.

The PHY-NGSC-Based ORT Run Length Encoding Scheme for Video Compression

This paper proposes a compression algorithm using octonary repetition tree (ORT) based on run length encoding (RLE). Generally, RLE is one type of lossless data compression method which has duplication problem as a major issue due to the usage of code word or flag. Hence, ORT is offered instead of using a flag or code word to overcome this issue. This method gives better performance by means of compression ratio, i.e. 99.75%. But, the functioning of ORT is not good in terms of compression speed. For that reason, physical- next generation secure computing (PHY-NGSC) is hybridized with ORT to raise the compression speed. It uses an MPI-open MP programming paradigm on ORT to improve the compression speed of encoder. The planned work achieves multiple levels of parallelism within an image such as MPI and open MP for parallelism across a group of pictures level and slice level, respectively. At the same time, wide range of data compression like multimedia, executive files and documents are possible in the proposed method. The performance of the proposed work is compared with other methods like accordian RLE, context adaptive variable length coding (CAVLC) and context-based arithmetic coding (CBAC) through the implementation in Matlab working platform.

Improved joint algorithms for reliable wireless transmission of 3D color-plus-depth multi-view video

Error control techniques like Error Resilience (ER) and Error Concealment (EC) are preferred techniques to ameliorate the lost Macro-Blocks (MBs) in the 3D Video (3DV) communication systems. In this paper, we present different enhanced ER-EC algorithms for intra-frame images for 3DV and Depth (3DV + D) communication through wireless networks. At the encoder, the slice structured coding, explicit flexible macro-block ordering, and context adaptive variable length coding are utilized. At the decoder, a hybrid approach comprising spatial circular scan order interpolation algorithm and temporal partitioning motion compensation algorithm is suggested to reconstruct the Disparity Vectors (DVs) and Motion Vectors (MVs) of the erroneous color images. For the corrupted depth images, a depth-assisted EC algorithm is proposed. Then, the optimum concealment MVs and DVs are chosen by employing the weighted overlapping block motion and disparity compensation algorithm. Furthermore, the Bayesian Kalman Filter (BKF) is utilized as an amelioration tool due to its efficiency to smooth the remnant inherent corruptions in the formerly optimally chosen color and depth DVs and MVs to obtain a good video quality. Simulation results on several 3DV streams show that the suggested algorithms have extremely adequate subjective and objective video quality performance compared to the traditional methods, particularly at high Packet Loss Rates (PLRs).

Improving Efficiency of Entropy Coding Method in Modern Video Compression Standards

Modern video coding standards have high coding efficiency, but the encoding performance has to be improved to meet the growing multimedia applications. The paper deals with the entropy encoding methods and algorithms in video coding standard H.264/AVC and H.265/HEVC. Context-based Adaptive Variable Length Coding (CAVLC) for the H.264/AVC standard was originally designed for lossy video coding, and as such does not yield adequate performance for lossless video coding. Context-Adaptive Binary Arithmetic Coding (CABAC) is a method of entropy coding first introduced in H.264/AVC and now used in the standard H.265/HEVC. While it provides high coding efficiency, the data dependencies in H.264/AVC CABAC make it challenging to parallelize and thus, limit its throughput. Accordingly, during the standardization of entropy coding for HEVC, both coding efficiency and throughput were considered. Based on an analysis of their advantages and disadvantages, a method called the entropy coding algorithm using the enumerative coding of the hierarchical approach is proposed. The proposed algorithm consists of the Context-Adaptive Binary Arithmetic Coding algorithm and the enumerative coding algorithm with a hierarchical approach. The proposed algorithm is tested in the Visual C ++ development environment on various test video sequences. The results of the experiments showed a greater efficiency of coding of multimedia data (the proposed one reduces on average up to 15% of the storage volume compared to the traditional CABAC method), while the method requires a longer coding time (approximately twice). The proposed method can be recommended for use in telecommunication systems for storage, transmission and processing of multimedia data, where a high degree of compression is required first.

Proposed adaptive joint error‐resilience concealment algorithms for efficient colour‐plus‐depth 3D video transmission

The authors propose efficient hybrid error resilience and error concealment (ER-EC) algorithms for H.264 3D video-plus-depth (3DV + D) transmission over error-prone channels. At the encoder, content-adaptive pre-processing ER mechanisms are implemented by applying the context adaptive variable length coding (CAVLC), the slice structured coding, and the explicit flexible macro-block ordering. At the decoder, a post-processing EC algorithm with multi-proposition schemes is implemented to recover the lost 3DV colour frames. The convenient EC hypothesis is adopted based on the lost macro-blocks size mode, the faulty view, and the frame types. For the recovery of the lost 3DV depth frames, an encoder-independent decoder-dependent depth-assisted EC algorithm is suggested. It exploits the previously estimated colour disparity vectors (DVs) and motion vectors (MVs) to estimate more additional depth-assisted MVs and DVs. After that, the optimum colour-plus-depth DVs and MVs are accurately selected by employing the directional interpolation EC algorithm and the decoder MV estimation algorithm. Finally, a weighted overlapping block motion and disparity compensation scheme is utilised to reinforce the performance of the proposed hybrid ER-EC algorithms. Experimental results on standard 3DV + D sequences show that the proposed hybrid algorithms have superior objective and subjective performance indices.

Secure chaotic dual encryption scheme for H.264/AVC video conferencing protection

This study presents a chaos-based crypto-compression scheme to protect the H.264 advanced video coding (AVC) used for the applications of video conference. To this end, a selective encryption approach was adopted. The authors proposed to encrypt the inter-prediction, the intra-prediction and the context adaptive variable length coding. The format compliance and compression ratio are conserved. Their encryption method is based on two piecewise linear chaotic maps for pseudo-random bit generators. The first is considered as a decision module to choose either to encrypt or not, whereas the second is used for the encryption. The proposed encryption techniques were developed and discussed, and their experimental results indicate that the scheme is secure and very efficient according to the computing times. Moreover, it is suitable for real-time application and convenient for all the H.264/AVC profiles or even with other video compression standards.

Effective multi-stage error control algorithms for robust 3D video transmission over wireless networks

The Three-Dimensional Video (3DV) contains diverse video streams taken by different cameras around an object. Thence, it is an imperative assignment to fulfill efficient compression to match the future resource limitations, whilst preserving a decisive reception 3DV quality. The efficient 3DV communication over wireless networks has become a recent considerable hot issue due to the restricted resources and the presence of severe channel errors. The high-rate 3DV encoding and transmission over mobile or Internet are vulnerable to packet losses due to the existence of heavy channel losses and limited bandwidth. Therefore, this paper presents efficient multi-stage error control algorithms for reliable 3DV transmission over error-prone wireless channels. At the encoder, the error resilience schemes of context adaptive variable length coding, slice structured coding, and explicit flexible macro-block ordering are utilized. At the decoder, a joint approach of a directional interpolation error concealment algorithm and a directional textural motion coherence algorithm is proposed to conceal the corrupted color frames. For the concealment of the lost depth frames, an encoder independent decoder dependent depth-assisted error concealment algorithm is suggested. Moreover, the weighted overlapping block motion and disparity compensation algorithm is exploited to choose the candidate concealment Motion Vectors (MVs) and Disparity Vectors (DVs). Furthermore, an improved recursive Bayesian filtering algorithm is utilized as a refinement stage to smooth the remaining errors in the previously selected candidate MVs and DVs for achieving better 3DV quality. Simulation results on several 3DV sequences show that the proposed algorithms achieve adequate objective and subjective 3DV quality performance at severe packet loss rates compared to the state-of-the-art algorithms.

A Comparative Evaluation Between CABAC and CAVLC

Abstract Lossless video coding improves the coding efficiency of the standard H.264/AVC. In this work, we adjusted the standard H.264/AVC to make it conservative. We removed the quantification process of the standard H.264/AVC coding chain because this block is the first responsible for the degradation of the reconstructed video. In the framework of the lossless compression, we compared two entropy codings: CABAC (context-based adaptive binary arithmetic coding) and CAVLC (context-based adaptive variable length coding). The simulation results showed that CABAC reduces the total bit of the coded sequence, but increased the execution time compared to CAVLC. Thanks to the lossless video coding, the gain performance reached from 15 to 19 %.

An efficient hardware architecture of CAVLC encoder based on stream processing

The paper presents an efficient implementation of Context-Adaptive Variable Length Coding (CAVLC) entropy encoder in H.264/AVC standard. The architecture is designed with a parallel structure targeting real-time video compression. The intensive memory access demand in the syntax element coding stage is lowered by using the proposed arithmetic table elimination technique. The packing stage implementation is interleaved with syntax element generation stage and includes fast methods for syntax elements concatenation. The register update method performs concatenation of the bitstream of previously processed sub-blocks and the syntax codewords of the currently processed sub-block. The CAVLC encoder processes 4 × 4 sub-block coefficients in parallel, introducing the initial latency of 12 clock cycles, after which the full pipeline of the data encoding on the sub-block level is performed, and 16 residuals are processed at each clock cycle. The achieved high throughput allows the encoding core to perform real-time processing of 8K UHD (4320p) video sequences with a frame rate of 30 frames/s.

Application-Guided Power-Efficient Fault Tolerance for H.264 Context Adaptive Variable Length Coding

This paper presents a fault-tolerance technique for H.264's Context-Adaptive Variable Length Coding (CAVLC) on unreliable computing hardware. The application-specific knowledge is leveraged at both algorithm and architecture levels to protect the CAVLC process (especially context adaptation and coding tables) in a reliable yet power-efficient manner. Specifically, the statistical analysis of coding syntax and video content properties are exploited for: (1) selective redundancy of coefficient/header data of video bitstreams; (2) partitioning the coding tables into various sub-tables to reduce the power overhead of fault tolerance; and (3) run-time power management of memory parts storing the sub-tables and their parity computations. Experimental results demonstrate that leveraging application-specific knowledge reduces area and performance overhead by 2x compared to a double-parity table protection technique. For functional verification and area comparison, the complete H.264 CAVLC architecture is prototyped on a Xilinx Virtex-5 FPGA (though not limited to it).

An information hiding method based on context-based adaptive variable length coding

Current video information hiding algorithms based on H.264 cannot meet the requirement of real-time transmission and get compromise between embedding strength and the changing amplitude of bits stream. To solve these problems, a real-time video information hiding method in CAVLC for H.264/AVC is proposed, which combines information hiding with CAVLC process, and embeds the secret information in the number of trailing coefficients of 4 × 4 macroblocks. Aiming at alleviating video degradation and the embedded secret in real-time transmission, the method is time-efficient and robust. Experimental results show that the embedding process cannot bring detectable video degradation, and only cause a small change in the length of the video stream. Moreover, the embedded secret information can be recovered correctly when being transferred under different RTP lost channels. And the secret information can be extracted directly from the encoded stream without resorting to the original video.

An information hiding method based on context-based adaptive variable length coding

Current video information hiding algorithms based on H.264 cannot meet the requirement of real-time transmission and get compromise between embedding strength and the changing amplitude of bits stream. To solve these problems, a real-time video information hiding method in CAVLC for H.264/AVC is proposed, which combines information hiding with CAVLC process, and embeds the secret information in the number of trailing coefficients of 4 × 4 macroblocks. Aiming at alleviating video degradation and the embedded secret in real-time transmission, the method is time-efficient and robust. Experimental results show that the embedding process cannot bring detectable video degradation, and only cause a small change in the length of the video stream. Moreover, the embedded secret information can be recovered correctly when being transferred under different RTP lost channels. And the secret information can be extracted directly from the encoded stream without resorting to the original video.

Highly Secure and Fast Video Encryption Using Minimum Overhead in H.264/AVC Bitstream

Abstract This paper primarily focuses on the encryption method used to design a selective video encryption scheme to meet following objectives. Encryption and decryption are able to secure in bits-level cryptographic security (after encryption), as well as in the pixel-level visual content security (after decoding for unauthorized user) to meet with sensitive video applications with minimum encryption overhead. It provides perceptual encryption with total scrambling of visual content. Besides, it also makes provision for randomness, not only in spatial but also in the temporal domain. It is presumed that an overall encryption and decryption scheme is quick enough to meet real-time applications. There is no change in the quality of video for genuine users. However, these objectives have been achieved in our proposed algorithm in expense of slight changes in compression bandwidth. The proposed algorithm encrypts residue data and motion vectors after entropy encoding to scramble spatial and temporal resolution. Encryption of motion vectors is based on Expo-Golomb entropy coding in inter-coded macroblock and DC value of residues is encrypted based on context-adaptive variable-length coding (CAVLC) in intra-coded macroblock. In addition, encryption is carried out using an advanced encryption system (AES) in a counter mode stream cipher. The paper deals with security analysis of a proposed scheme in terms of cryptography, as well as perception security.

Joint Selective Encryption of CAVLC and Signs of Motion Vectors for H.264/AVC

Abstract Currently, researchers are orienting their effort to selective encryption in order to protect video sequences against attacks during their transmission over a public channel. The reasons for this trend are of great importance. To reduce video data amount, the video compression chain is essential and to ensure their security, while in transmission, an encryption algorithm is evident. Thus, inserting the encryption module in the video compression chain is better than applying compression and encryption separately in terms of computing time. This paper presents a chaos based encryption method inserted in the H.264 Advanced Video Coding (AVC) used for video conferencing applications. The selective encryption was applied on context adaptive variable length coding (CAVLC) and on the signs of motion vectors. The results were deducted according to the values of peak signal to noise ratio (PSNR), structural similarity (SSIM) and the encryption rate (ER). Combining selective encryption of CAVLC (SE-CAVLC) and motion vector sign encryption (MVSE) are interesting in terms of enhancing the encryption and to damage the visual quality of the decoded video for both Intra and Inter predicted frames.

A Novel Steganography Technique for SDTV-H.264/AVC Encoded Video

Today, eavesdropping is becoming a common issue in the rapidly growing digital network and has foreseen the need for secret communication channels embedded in digital media. In this paper, a novel steganography technique designed for Standard Definition Digital Television (SDTV) H.264/AVC encoded video sequences is presented. The algorithm introduced here makes use of the compression properties of the Context Adaptive Variable Length Coding (CAVLC) entropy encoder to achieve a low complexity and real-time inserting method. The chosen scheme hides the private message directly in the H.264/AVC bit stream by modifying the AC frequency quantized residual luminance coefficients of intrapredicted I-frames. In order to avoid error propagation in adjacent blocks, an interlaced embedding strategy is applied. Likewise, the steganography technique proposed allows self-detection of the hidden message at the target destination. The code source was implemented by mixing MATLAB 2010 b and Java development environments. Finally, experimental results have been assessed through objective and subjective quality measures and reveal that less visible artifacts are produced with the technique proposed by reaching PSNR values above 40.0 dB and an embedding bit rate average per secret communication channel of 425 bits/sec. This exemplifies that steganography is affordable in digital television.

Implementing Entropy Codec for H.264 Video Compression Standard

Entropy coding is a lossless compression technique which is supported in H.264/AVC standard by different techniques. According to baseline and the extended profiles of H.264/AVC, two variable length techniques are for seen. The first one is context adaptive variable length coding (CAVLC) and the other is exponential Golomb (Exp-Golomb) one. The CAVLC is used to quantize transform residues after reordering them by ZigZag scanning while Exp-Golomb coding is used to quantize other syntax elements. Within the frame of realizing the whole H246 standards, this paper, introduces an implementation of these two codec techniques for baseline profile using Matlab and Simulink. The main concept is to implement CAVLC and Exp-Golomb decoder according to H.264/AVC standard and then device a technique to implement CAVLC & Exp-Golomb encoder. The different implementations are utilized to verify each other.

High-Throughput Reconfigurable Variable Length Coding Decoder for MPEG-2 and AVC/H.264

This paper presents a reconfigurable architecture for two video coding standards, MPEG-2 and AVC/H.264. The proposed reconfigurable architecture dynamically configures the architecture to achieve multiple functions in variable length coding decoder and context-adaptive variable length coding decoder. By means of extracting the commonalities at the low-level dataflow, the designed reconfigurable architecture optimizes hardware resources and increases architectural flexibility through the reconfigurability in the adaptively constructing architecture. On the other hand, the proposed reconfigurable architecture combines several strategies in AVC/H.264 mode, and subsequently revises and integrates these mechanisms to achieve a high-throughput rate. As a consequence, the memory usage of the proposed reconfigurable architecture achieves 37.5 % memory bits saving and 46.7 % memory area reduction as compared to the individual implementation; moreover, in AVC/H.264 mode, this reconfigurable architecture requires only 50 cycles to decode one marcoblock on average. Due to the flexibility, the proposed reconfigurable architecture costs 10.8 K gates by using 0.18 μm CMOS technology at the 108 MHz clock rate, and supports variable length coding in MPEG-2 with 1920?×?1080@30fps and context-adaptive variable length coding in AVC/H.264 with 1920?×?1080@60fps. From the perspectives of architectural costs and supported functions, the proposed architecture surpasses the related works in the state of the art.

Non-tables look-up search algorithm for efficient H.264/AVC context-based adaptive variable length coding decoding

In general, context-based adaptive variable length coding (CAVLC) decoding in H.264/AVC standard requires frequent access to the unstructured variable length coding tables (VLCTs) and significant memory accesses are consumed. Heavy memory accesses will cause high power consumption and time delays, which are serious problems for applications in portable multimedia devices. We propose a method for high-efficiency CAVLC decoding by using a program instead of all the VLCTs. The decoded codeword from VLCTs can be obtained without any table look-up and memory access. The experimental results show that the proposed algorithm achieves 100% memory access saving and 40% decoding time saving without degrading video quality. Additionally, the proposed algorithm shows a better performance compared with conventional CAVLC decoding, such as table look-up by sequential search, table look-up by binary search, Moon’s method, and Kim’s method.

A High-Throughout Design of CAVLC Decoder for H.264/AVC

In this paper, a novel high-throughput method is proposed to improve the decoding efficiency of the context-based adaptive variable length coding (CAVLC) procedure of H.264/AVC. Due to the data dependency among symbols in the entropy decoding flow, the CAVLC decoder requires large computation period, which dominates the overall decoder system performance. To expedite its decoding speed, the critical path in the CAVLC decoder is first analyzed. This paper presents a double level design for H.264/AVC CAVLC decoding. In the proposed design, we exploit a predict strategy to achieve double level decoding. Experimental results show that the operation period of the proposed architecture can be reduced about 28.3% compare with the tradition CAVLC architecture. The maximum frequency can be larger than 120 MHz, which can support the real time requirement.