H.323视频会议系统中的多线程技术解析

结合Win32平台下的多线程编程思想和方法，深入剖析H．323视频会议系统中各线程的协调机制，讨论了用C 语言实现多线程编程的技术。     

低比特率通信的H.263视频编解码

本文介绍了国际电联组织ITU-T 于1995年2月起草并通过的 H.263建议草案中低比特率视频编解码的原理、实现流程和图像的数据结构,并对H.263建议的4个增强编解码模式以及 H.263建议与H.261建议编解码的不同之处进行了探讨。     

H.263: video coding for low-bit-rate communication

This article provides an overview of H.263, the new ITU-T Recommendation for low-bit-rate video communication. H.263 specifies a coded representation for compressing the moving picture component of audio-visual signals at low bit rates. The basic structure of the video source coding algorithm is taken from ITU-T Recommendation H.261 and is a hybrid of interpicture prediction to reduce temporal redundancy and transform coding of the prediction residual to reduce spatial redundancy. The source coder can operate on five standardized picture formats: sub-QCIF, QCIF, CIF, 4CIF, and 16CIF. The decoder has motion compensation capability with half-pixel precision, in contrast to H.261 which uses full-pixel precision and employs a loop filter. H.263 includes four negotiable coding options which provide improved coding efficiency: unrestricted motion vectors, syntax-based arithmetic coding, advanced prediction, and PB-frames     

H.263建议的原理及其特点

本文讨论了ＩＴＵ－Ｈ．２６３建议的原理和它的一些主要特点，如ＰＢ帧模式，运动补偿、算术编码等，把它们与Ｈ．２６１建议和ＭＰＥＧ标准作了比较，并通过计算机模拟检验其效果。     

基于局域网的H.263视频数据流的实时传输

介绍了一种在局域网上利用RTP技术实时传输H.263图像数据的方法，并对其性能进行了测试，给出了C语言编程实例。通过RTP及RTCP提供的信息对编码端进行码率调整等方法，成功地实现了基于局域网的图像监控系统中的H.263图像数据的实时传送。     

H.263码流的RTP封装的研究与实现

在对RTP/RTCP特点与功能的研究、H.263视频数据的RTP封装格式研究和H.263码流结构分析的基础上,提出了一种将H.263码流封装成RTP数据包的实现方法.     

Video Transcoding with H.263 Bit-Streams

Video transcoding is one of the key technologies in implementing dynamic adaptation of the bit-rate of a coded video bit-stream to the available bandwidth over various networks. Many fast transcoder architectures have been proposed to achieve fast processing. However, they suffer from quality degradation caused by the drift error. In this paper, we investigate the drift caused by the fast transcoder architectures for transcoding H.263 bit-streams. We discuss the limitations of the fast transcoder architectures and the flexibility that can be offered by a cascaded pixel-domain transcoder. Since the cascaded pixel-domain transcoder can achieve drift-free performance, we also propose methods to reduce the computational complexity of the drift-free cascaded pixel-domain transcoder.     

Perceptual adaptive quantisation scheme for H.263 video coder

The authors propose an efficient perceptual adaptive quantisation scheme that uses Q-N (quantisation step-number of output bits) mapping tables and fuzzy perceptual classifiers. Using this adaptive quantisation scheme, stable perceptual quality and good visual effects can be obtained at a constant output bit rate     

Best packetisation scheme for H.263 Internet video communication

The H.263 codec is an efficient way to stream variable bit-rate video sequences. It is proposed that, for equivalent bandwidth and frame rate, a two-slice packetisation scheme results in superior peak signal-to-noise ratio, rather than the conventional one-slice scheme, and that constant inter-packet gap rather than 'bursty' delivery is preferable.     

Low-power data forwarding for VLIW embedded architectures

Proposes a low-power approach to the design of embedded very long instruction word (VLIW) processor architectures based on the forwarding (or bypassing) hardware, which provides operands from interstage pipeline registers directly to the inputs of the function units. The power optimization technique exploits the forwarding paths to avoid the power cost of writing/reading short-lived variables to/from the register file (RF). Such optimization is justified by the fact that, in application-specific embedded systems, a significant number of variables are short-lived, that is, their liveness (from first definition to last use) spans only few instructions. Values of short-lived variables can thus be accessed directly through the forwarding registers, avoiding writeback to the RF by the producer instruction and successive read from the RF by the consumer instruction. The decision concerning the enabling of the RF writeback phase is taken at compile time by the compiler static scheduling algorithm. This approach implies a minimal overhead on the complexity of the processor control logic and, thus, no critical path increase. The application of the proposed solution to a VLIW embedded core has shown an average RF power saving of 7.8% with respect to the unoptimized approach on the given set of target benchmarks.     

MPEG-4 and H.263 video traces for network performance evaluation

MPEG-4 and H.263 encoded video is expected to account for a large portion of the traffic in future wireline and wireless networks. However, due to a lack of sufficiently long frame size traces of MPEG-4 and H.263 encoded videos, most network performance evaluations currently use MPEG-1 encodings. We present and study a publicly available library of frame size traces of long MPEG-4 and H.263 encoded videos, which we have generated at the Technical University Berlin. The frame size traces have been generated from MPEG-4 and H.263 encodings of over 10 video sequences each 60 minutes long. We conduct a thorough statistical analysis of the traces     

用TMS320C6201实现H.263编译码系统

介绍了用TMS320C6201实现视频压缩编码标准H.263的编译码系统,并以编码系统为例,给出其硬件设计及软件的优化处理方法.     

A rate control scheme using Kalman filtering for H.263

This paper proposes a rate control framework for H.263 video coding called the low-delay Kalman filtering rate controller (LKFrc), whose main part is the adaptive Kalman filter. In LKFrc, a low-delay two-stage selector is proposed to select the representative frames of video. The first stage can rapidly pre-select the relatively significant frames. The second selection stage is embedded in the prediction model of Kalman filter. By the prediction model, LKFrc can distribute a proper bit budget to the pre-selected frame or definitely skip this frame. The measurement model of Kalman filter exploits a rate–distortion (R–D) model to meet the given bit budget by selecting an appropriate picture-level quantization parameter (QP). From the picture-level QP, the subsequent macroblock-level QPs are rapidly yielded by a rapid offset model using the relative macroblock activity. In comparison with the TMN8 model, the LKFrc framework can obtain better PSNRs, higher motion continuities and lower flickering effects with lower computation cost.     

Error concealment using affine transform for H.263 coded videotransmissions

A new error concealment method is proposed that uses motion estimation to consider actual motions, such as rotation, magnification, reduction, and parallel motion, in moving pictures. Since many videos include a variety of complex three-dimensional motions, the proposed method uses an affine transform to estimate the motion of lost data more accurately, thereby producing a higher peak signal-to-noise ratio value and better subjective video quality     

适用于H.263(+)的一种运动估计快速搜索算法

介绍了适合H.263的一种改进算法.改进的新三步法(improved NISS),基于NISS的改进方案,结合H.263(+)的高级选项使用时可以大大减少计算量.采用全搜索算法计算量最大,各种快速算法都是以限制搜索步骤或点数来换取计算量的大大减少,同时保证了性能的降低最小.无论运动图像剧烈与否,该方案都提出了克服的方法.实际测试表明改进的这种方法性能上几乎达到了全搜索法(FS)的结果,而时间上只有FS的5%左右.     

A PREDICTION BASED ALL—ZERO BLOCK DETECTION METHOD FOR H．263

In this letter,a novel method based on Temporal and Spatial Prediction(TSP)to detect all-zero DCT coefficients based on temporal and spatial prediction between neighboring blocks is proposed.The presented algorithm uses the knowledge of all-zero block distribution in the previous frame combined with the Sum of Absolute Difference(SAD)of the corresponding macroblock as a criterion .The algorithm almost needs no additional computation ,and it shows an excellent overall detection performance in simulations.     

A new rate control scheme for H.263 video transmission

In some image/video applications, the variable bit rate image/video bitstream will be transmitted over a constant bit rate transmission channel, in which a channel buffer is employed. In this study, a new rate control scheme for H.263 video transmission is proposed. Three proposed techniques include: preprocessing the INTRA coded macroblock (MB) incorporated the just-noticeable-distortion (JND) concept, constructing a bit estimation model in the frequency domain (instead of the bit estimation model in the spatial domain employed in Test Model Near-term version 11 (TMN11)), and adjusting quantization parameter (QP) for each MB by a Lagrangian optimization strategy.In the proposed approach, the target number of bits for a video frame is first obtained by using a simple rate control procedure for the frame layer. The proposed JND preprocessing is applied on all the INTRA coded MBs so that the number of coded bits for a scene changed frame will decrease, without any perceptual loss. Within the MB layer, instead of the bit estimation model in the spatial domain employed in TMN11, a bit estimation model in the frequency domain, directly depending on discrete cosine transform coefficients, is proposed. Then the Lagrange multiplier is used to determine the optimal QP for each MB. The resulting QP and number of coded bits of the current MB are fed backward to update the parameters of the bit estimation model.Based on the simulation results obtained in this study, the proposed approach can meet the target bit rate more accurately, keep a lower channel buffer fullness (delay), and have a larger average frame rate than TMN11, whereas the peak signal-to-noise ratio value and the processing time of the proposed approach are “approximately” as good as that of TMN11.     

Improvement of Matching Criterion for Motion Estimation in H.263

ＩｍｐｒｏｖｅｍｅｎｔｏｆＭａｔｃｈｉｎｇＣｒｉｔｅｒｉｏｎｆｏｒＭｏｔｉｏｎＥｓｔｉｍａｔｉｏｎｉｎＨ．２６３ＱｉｕＪｕｎｈａｉＺｈａｎｇＣｈｕｎｔｉａｎ（ＴｉａｎｊｉｎＵｎｉｖｅｒｓｉｔｙ，Ｔｉａｎｊｉｎ３０００７２）ＡｂｓｔｒａｃｔＴｈｅｒｅ...     

一种改善H.263图像质量的方法

提出了一种保护图像中最重要的边缘信息的量化策略.仿真结果表明,与普通量化方法(如TMN系列代码)相比,新方法以较小的运算量为代价使边缘信息得到有效保护,从而在降低码率的同时更好地保持了图像的质量.     

基于H.263中PEI域的视频抗误码方法研究

本文提出利用H.263中PEI域自适应改变前向纠错能力,保护重同步信息进行误码掩盖,以及防止误码扩散的一种新颖的抗误码方法.实验结果表明,在信道变化和高误码率环境下,使用本文提出的抗误码方法大大提高了恢复视频的质量.另外,该算法与H.263标准兼容,且没有过多增加信道负担和运算复杂度,具有实用价值.