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.     

Balancing MPEG Transcoding with Storage in Multiple-Quality Video-on-Demand Services

To match the requirements of heterogeneous mobile devices, video objects may be transcoded, which requires considerable CPU resources. Alternatively, multiple versions of the same video may be stored on servers, but this requires a lot of disk space. We formulate the trade-off between the versions that are stored on disk and the need for transcoding. We propose an optimal solution to this formulation based on dynamic programming. Experiments show that our scheme allows up to 68% more clients to be admitted than conventional schemes when a reasonable amount of storage is available.     

On modeling MPEG video traffics

This paper traces the development/evolution of three of our previously proposed MPEG coded video traffic models, that can capture the statistical properties of MPEG video data. The basic ideas behind these models are to decompose an MPEG compressed video sequence into several parts according to motion/scene complexity or data structure. Each part is described by a self-similar process. These different self-similar processes are then combined to form the respective models. In addition, Beta distribution is used to characterize the marginal cumulative distribution (CDF) of the self-similar processes. Comparison among the three models shows that the latest model (called the simple IPB composite model) is the most practical one in terms of accuracy and complexity. Simulations based on many real MPEG compressed movie sequences, including StarWars, have demonstrated that the simple model can capture the autocorrelation function (ACF) and the marginal CDF very closely.     

Super-resolution mosaicing from MPEG compressed video

In this paper we address the problem of mosaic construction from MPEG 1/2 compressed video for the purpose of video browsing. State-of-the-art mosaicing methods work on raw video, but most video content is available in compressed form such as MPEG 1/2. Applying these methods to compressed video requires full decoding which is very costly. The resulting mosaic is in general too large to display on the screen and is thus inappropriate for the purpose of video browsing. Therefore, we directly extract very low-resolution frames from MPEG 1/2 compressed video for the mosaic construction and then apply a super-resolution (SR) method based on iterative backprojections in order to increase the mosaic resolution and its visual quality. Global motion to be used in the SR method for aligning and warping the frames is estimated from motion information contained in the compressed stream. We also use the estimated global motion in the blur estimation and in the choice of the degradation model used for the restoration in the SR algorithm. The method for the SR mosaic construction from MPEG 1/2 compressed video that we present in this paper is less costly than mosaic construction from full decoded video. Furthermore, the resulting mosaic size is more appropriate for the purpose of video browsing.     

基于视频内容的MPEG视频VBR业务流量模型

视频业务流量模型是网络性能仿真的一个重要前置环节,但由于视频内容的千差万别,使得很难建立统一的视频业务流量模型。本文根据MPEG视频图像内容的纹理及运动复杂度,通过3×3 Kohonen自组织神经网络对视频序列进行划分,将其分割为一段段近似平稳的“视频片段”。然后,用半马尔可夫随机过程描述“视频片段”间的转移概率及其持续时间分布规律,用AR模型描述“视频片段”内部过程,从而建立了一种通用MPEG视频业务流量模型。     

A framework for end-to-end video quality prediction of MPEG video

This paper proposes, describes and evaluates a novel framework for video quality prediction of MPEG-based video services, considering the perceptual degradation that is introduced by the encoding process and the provision of the encoded signal over an error-prone wireless or wire-line network. The concept of video quality prediction is considered in this work, according to which the encoding parameters of the video service and the network QoS conditions are used for performing an estimation/prediction of the video quality level at the user side, without further processing of the actual encoded and transmitted video content. The proposed prediction framework consists of two discrete models: (i) a model for predicting the video quality of an encoded signal at a pre-encoding stage by correlating the spatiotemporal content dynamics to the bit rate that satisfies a specific level of user satisfaction; and (ii) a model that predicts primarily the undecodable frames (and subsequently the perceived quality degradation caused by them) based on the monitored averaged packet loss ratio of the network. The proposed framework is experimentally tested and validated with video signals encoded according to MPEG-4 standard.     

实时性MPEG视频源的图片组内平滑算法

本文对实时性的ＭＰＵＥＧ视频源进行了平滑研究,通过分析ＭＰＥＧ视频编码的特点和实时性ＶＢＲ视频对延迟的严格要求,提出实时性ＭＰＥＧ视频在图片组（ＧＯＰ）内平滑已接近最佳平滑的观点,并推导了图片组内平滑的上限速率和下限速率公式,设计了选择最佳速率的算法,最后使用两组代表不同应用的ＭＰＥＧ视频样本数据进行了仿真实验。实验表明：图片组内平滑算法与文献上其它算法相比,在理论上可取得几乎相同的理想平滑效果,     

MPEG coding for variable bit rate video transmission

For real-time transmission of broadcast-quality video on ATM-based B-ISDN, the intraframe to interframe ratio and the quantizer scale are two key parameters that can be used to control a video source in a network environment. Their impact on the traffic characteristics of the coder provides insights into the cell arrival process for an MPEG source. The authors obtain video source models for coders that utilize a standard algorithm that can be applied to a multitude of video services. The output stream of a video coder, which complies with the Motion Pictures Expert Group (MPEG) coding standard, is studied with an National Television Systems Committee (NTSC) quality video sequence as the input. Because the MPEG video coding algorithm has been proposed for a variety of applications, they also investigate the effect of changing the coding parameters on the statistics of interest     

A GACS modeling approach for MPEG broadcast video

Accurate MPEG source models are needed to support high speed networks such as ATM and Internet. In this paper, we propose a video model called Gaussian auto-regressive and chi-square processes (GACS) for MPEG coded video traffic. The GACS models the sizes of MPEG I, P, and B frames according to the MPEG syntax I-frame>P-frame>B-frame. This is done by decomposing the process of each frame size into a weighted sum of a number of chi-square sequences. Each chi-square sequence is then obtained by squaring a Gaussian process, which is efficiently generated by using an auto-regressive (AR) model whose parameters are determined from an estimated covariance matrix. We evaluate the effectiveness of our model by conducting a series of experiments using a wide variety of long empirical video sequences. The results show that the proposed model leads to excellent data fit and accurate prediction of queuing performance.     

An objective measurement tool for MPEG video quality

A two-stage objective measurement model for MPEG-coded video is proposed. The first stage weights the coded video distortion according to the human visual system's response. It computes the frame-by-frame perceptual impairment in the decoded picture with respect to a reference picture; this includes low-pass spatial filtering, a Sobel operation to derive masking coefficients, and spatial masking on the raw error between reference and compressed pictures. The second stage, a cognitive emulator, provides a simulation of human high-level processing of visual information. This includes the very low temporal response of human viewers to image quality changes, and asymmetric behaviour in respect of picture quality changes from bad to good, and vice versa. With this model, we have been able to mimic quite accurately the temporally varying subjective picture quality of video sequences as recorded by the ITU-R SSCQE method.     

Supporting MPEG video transport on DOCSIS-compliant cable networks

A novel quality of service (QoS) scheduling mechanism suitable for transporting variable bit rate video in the upstream direction over a DOCSIS (data over cable system interface specification)-compliant cable network is presented. It is shown, via simulation using real life video traces, that the proposed scheduling service provides significant improvements as compared to the existing DOCSIS QoS scheduling services, with regard to bandwidth utilization and latency distribution. The proposed scheduling service is also applicable to transport integrated services over the Internet and can be utilized by other emerging multimedia applications, where data are bursty in nature and variable in bit rate     

Simulation study on ATM multiplexing of MPEG video sources

In this paper we study the performance of ATM multiplexing of homogeneous MPEG video sources. A source scheduling method is developed to improve the performance of ATM multiplexer for MPEG video sources. Simulation results show that the level of burstiness for the aggregated MPEG traffic is reduced and the network performance is enhanced. Based on the rationale of the source scheduling method, a simple but efficient bandwidth allocation algorithm is also derived for connection admission of MPEG video in an ATM multiplexer. Copyright © 2001 John Wiley & Sons, Ltd.     

Rate control of MPEG video for consistent picture quality

We propose a rate control scheme using a rate-distortion (R-D) estimation model, which produces a consistent picture quality between consecutive frames. Our R-D estimation method offers a closed-form mathematical model that enables us to predict the bits and the distortion generated from a frame encoded at a given quantization parameter (QP) and vice versa. Its most attractive feature is its low computational complexity. Furthermore, it is accurate enough to be applied to practical video coding. In our simulation, the estimation errors for rate and distortion are less than 2.5% and 1.5%, respectively. Therefore, the proposed rate control scheme is appropriate for applications requiring low delay, low complexity, and the ability to control output bit-rate and quality accurately. Our scheme ensures that the video buffers do not underflow or overflow by satisfying the buffer constraint, and it also prevents quality difference between consecutive frames from exceeding a certain demanded level by adopting a distortion constraint. In addition, a consistent picture quality is maintained within a frame, and error propagation, caused by quality degradation of anchor frames, is reduced by differentiating the control procedure for anchor frames from that for nonanchor frames. Simulation results show that our control scheme achieves 0.52-1.84 dB peak signal-to-noise ratio (PSNR) gain over MPEG-2 Test Model 5 (TM5) rate control and maintains very consistent quality within a frame as well as between frames.     

Interleaving schemes for ATM multiplexing of MPEG video sources

The authors analyse the performance of two interleaving schemes, called frame-oriented and cell-oriented, for statistical multiplexing of MPEG video sources. Simulations using two long MPEG sequences show that there is a trade-off in cell loss probability and delay jitter when selecting the interleaving scheme     

A MPEG video structure analysis scheme and its application to hierarchical video browser

This paper presents a novel scheme that automatically extracts out the hierarchical structure of MPEG video by detecting cuts and scenes, and a very userfriendly hierarchical video browser. The proposed scheme first conducts a fast, robust cut detection, chooses the representative frames of shots through clustering, calculates the connectivity between shots based on the similarities of the shots including a certain number of neighbors by using fuzzy reasoning, and extracts scenes by examining the connectivity change. The scheme is overall robust against threshold setting, cut missdetection and overdetection. We applied our scheme to parts of movies, the cut and scene detection rates are respectively higher than 95% and 75%. Considering the scheme is of high speed and in no need of knowledge on specific kinds of videos, these detection rates are quite satisfactory. The scheme is also feasible for other kinds of videos if they possess the feature that scene consists of a group of similar shots.     

MPEG4视频压缩编码技术及应用

MPEG4是国际标准组织制定的多媒体通信的标准，文中概述了MPEG4的背景，MPEG4与MPEG1，MPEG2的主要区别以及MPEG4的主要技术。最后，展望了MPEG4的应用前景。     

MPEG2视频解码器系统的总线仲裁设计

mpeg2的视频解码过程需要对片外存储器频繁的访问,在单总线结构的系统中,选取一定的总线仲裁策略以达到减少访问冲突,充分利用总线资源的目的.本文实现了解码系统中子模块与总线的接口电路,给出了不同仲裁策略下的RTL级仿真结果.     

An adaptive temporal-spatial filter for MPEG decoded video signals

A new adaptive post-processing algorithm for the MPEG decoded video sequences is proposed. We use a motion compensated averaging filter to reduce the noises in the temporal domain and an adaptive spatial filter to remove noise in the spatial domain and preserve the edge of different orientations in the image. A MPEG decoded video sequence called table tennis is processed by our proposed filter. The post-processed video sequence shows that its image quality is improved, especially of the moving objects.     

Combining visual MPEG tools in the context of video adaptability

This paper proposes an interworking between MPEG-2 Intraframe coding and JPEG2000 international standards. The latter codec is integrated into the base layer of spatial scalability encoders whilst retaining full compatibility with MPEG-2 decoders. The proposed solution combines existing ISO/IEC MPEG standards and is elaborated upon with respect to three application areas; bitstream format portability and adaptability, bitstream switching and combined video scalability. The paper elaborates upon the proposed coding architectures and compatibility with published MPEG standards. The proposed coding architecture is compared against counterpart video transcoders, scalable and single layer codecs. It is shown that the proposed spatial encoder is superior to all the aforementioned codecs whilst enjoying an extensible architecture capable of serving restricted end systems and hosting additional scalable layers such as SNR and temporal scalabilities.