On modeling and evaluating multicomputer transcoding architectures for live-video streams

The pervasive and ubiquitous computing has motivated researches on multimedia adaptation which aims at matching the video quality to the user needs and device restrictions. This technique has a high computational cost which needs to be studied and estimated when designing architectures and applications. This paper presents an analytical model to quantify these video transcoding costs in a hardware independent way. The model was used to analyze the impact of transcoding delays in end-to-end live-video transmissions over LANs, MANs and WANs. Experiments confirm that the proposed model helps to define the best transcoding architecture for different scenarios.     

高清制播平台的嵌入式移动回传转码系统设计

本文通过对移动回传转码系统需求的梳理,引出流程设计、各主要功能模块的功能设计、网络架构设计等方面,并重点对该系统嵌入高清制播平台的重要环节——转码入库功能进行阐述,合理规划了移动回传转码系统嵌入高清制播平1台的方案.站在安全、可扩展性的角度,实现上海电视台五星体育、第一财经等现有高清制播平台能力的深度挖掘.     

The Personal Presence System: a wide-area network resource for the real-time composition of multipoint multimedia communications

The Personal Presence System (PPS) is an experimental research prototype platform to support advanced broadband applications, including multimedia conferencing and distance learning. It supports the user's presentation control of advanced network elements (multimedia bridges). The multimedia bridge provides for a single contact point per user, who receives only one combined video stream, which minimizes access bandwidth. This architecture solves the -squared transmission problem of multipoint video conferencing and makes customer terminal equipment simpler and cheaper than high-end desktop workstations. The PPS provides each user with flexible presentation control of a feature-rich video bridge. The PPS also supports advanced features such as object extraction and multimedia object associations.     

Mixed architectures for H.264/AVC digital video transrating

In this paper, we investigate transrating architectures for H.264/AVC video streams. Basic architectures are presented with their strengths and weaknesses. None of the existing architectures provide an appropriate solution for H.264/AVC transrating with an optimal balance between visual quality and complexity. In order to find such an appropriate solution, we propose the use of mixed transrating architectures. These architectures combine different transrating techniques which are applied depending on the picture/macroblock type. The intra-predicted pictures are decoded and re-encoded, while open-loop transrating or transrating with compensation is applied to motion-compensated pictures. Performance results show that the mixed architecture which applies spatial compensation to motion-compensated pictures gives rate-distortion results which approach the cascade of decoder and re-encoder with a complexity only slightly higher than the open-loop transrater. Adding temporal compensation for motion-compensated pictures further improves the visual quality, albeit to a lower extent, at the expense of increased complexity.

Transcoding of MPEG bitstreams

This paper discusses the problem of transcoding as it may occur in, for instance, the following situation. Suppose a satellite transmits an MPEG-compressed video signal at say 9 Mbit/s. This signal must be relayed at a cable head end. However, since the cable capacity is only limited, the cable head end will want to relay this incoming signal at a lower bit-rate of, say, 5 Mbit/s. The problem is how to convert a compressed video signal of a given bit-rate into a compressed video signal of a lower bit-rate. The specific transcoding problem discussed in this paper is referred to as bit-rate conversion. Basically, a transcoder used for such a purpose will consist of a cascaded decoder and encoder. It is shown in the paper that the complexity of this combination can be significantly reduced. The paper also investigates the loss of picture quality that may be expected when a transcoder is in the transmission chain. The loss of quality as compared to that resulting in the case of transmission without a transcoder is studied by means of computations using simplified models of the transmission chains and by means of using computer simulations of the complete transmission chain. It will be shown that the presence of two quantizers, i.e. cascaded quantization, in the transmission chain is the main cause of extra losses, and it will be shown that the losses in terms of SNR will be some 0.5 – 1.0 dB greater than in the case of a transmission chain without a transcoder.     

FITD: Fast Intra Transcoding from H.264/AVC to high efficiency video coding based on DCT coefficients and prediction modes

In the literatures, the designs of H.264 to High Efficiency Video Coding (HEVC) transcoders mostly focus on inter transcoding. In this paper, a fast intra transcoding system from H.264 to HEVC based on discrete cosine transform (DCT) coefficients and intra prediction modes, called FITD, is proposed by using the intra information retrieved from an H.264 decoder for transcoding. To design effective transcoding strategies, FITD not only refers block size of intra prediction and intra prediction modes, but also effectively uses the DCT coefficients to help a transcoder to predict the complexity of the blocks. We successfully use DCT coefficients as well as intra prediction information embedded in H.264 bitstreams to predict the coding depth map for depth limitation and early termination to simplify HEVC re-encoding process. After a HEVC encoder gets the prediction of a certain CU size from depth map, if it reaches the predicted depth, the HEVC encoder will stop the next CU branch. As a result, the numbers of CU branches and predictions in HEVC re-encoder will be substantially reduced to achieve fast and precise intra transcoding. The experimental results show that the FITD is 1.7–2.5 times faster than the original HEVC in encoding intra frames, while the bitrate is only increased to 3% or less and the PSNR degradation is also controlled within 0.1 dB. Compared to the previous H.264 to HEVC transcoding approaches, FITD clearly maintains the better trade-off between re-encoding speed and video quality.     

减少码率变换再量化误差的优化方案

阐述了码率变换再量化过程中再量化误差的产生及其实质,给出了应用最小均方误差（MSE）准则减少再量化误差的原理,在码率变换再量化器一端,根据首次量化值在量化区间的概率分布中心决定该量化值的区间,有效地消除了量化区间跨区交叠所引入的再量化误差,给出了减少再量化误差方案的实现步骤。实验和模拟结果均表明：该方案有效地减少了再量化误差,获得了较好的图像质量。     

Machine learning based fast H.264/AVC to HEVC transcoding exploiting block partition similarity

Video transcoding is to convert one compressed video stream to another. In this paper, a fast H.264/AVC to High Efficiency Video Coding (HEVC) transcoding method based on machine learning is proposed by considering the similarity between compressed streams, especially the block partition correlations, to reduce the computational complexity. This becomes possible by constructing three-level binary classifiers to predict quad-tree Coding Unit (CU) partition in HEVC. Then, we propose a feature selection algorithm to get representative features to improve predication accuracy of the classification. In addition, we propose an adaptive probability threshold determination scheme to achieve a good trade-off between low coding complexity and high compression efficiency during the CU depth prediction in HEVC. Extensive experimental results demonstrate the proposed transcoder achieves complexity reduction of 50.2% and 49.2% on average under lowdelay P main and random access configurations while the rate-distortion degradation is negligible. The proposed scheme is proved more effective as comparing with the state-of-the-art benchmarks.     

Effective algorithms for fast transcoding of AVS to H.264/AVC in the spatial domain

This paper proposes a transcoding scheme from AVS to H.264/AVC. As high-compression video coding standards, H.264/AVC jointly developed by MPEG and ITU and AVS developed by the Audio Video Coding Standard Working Group of China will co-exist in the future market. Therefore, it is worthy to transcode the AVS format to the H.264/AVC format or vice versa. After an insight into the inter transcoding from AVS to H.264/AVC, a simple and effective method is proposed by reusing the mode and motion vectors to achieve high-efficient and fast transcoding. The problem in reusing the skip mode is studied and an effective method to eliminate the artifacts is proposed. Furthermore, a fast intra transcoding algorithm based on the distribution of the DCT coefficients is proposed to speed up the transcoding process. Detailed experiment results demonstrate that the proposed algorithm can effectively reduce the transcoding complexity.

一种自适应运动估值视频代码转换的新方法

针对窄带网络的视频信号传输问题,分析了传统视频代码转换帧速率转换时,由于运动矢量非最佳化所造成的图象质量下降的原因,并提出了一种基于量化误差的自自动化运动矢量模型,从而减小了搜索域,使最佳化输出运行矢量能进行快速运动估值;同时根据灰度系统理论,提出了一种有效的灰度预测搜索方法,另外,又根据DCT系数理论模型。采用自适应快速视频编码方法,进一步提高了编码速度,实验结果表明：该方法不仅改善了视频图象质量,而且计算复杂度也大大减小。