Variable Bit Rate Video Research Articles

Shifting-level process as a LRD video traffic model and related queuing results

Recently it has been reported that variable bit rate (VBR) video traffic exhibits long-range dependence (LRD). Various processes have been proposed for modeling traffic with LRD and analyzing its effects on network performance. However, in the previous models it is not possible to identify the effects of short- and long-term correlation of video traffic on queuing performance, and thus many seemingly contradictory arguments on the importance of LRD in VBR video traffic can be found in the literature. In this paper, we present a video traffic model based on the shifting-level ( SL) process. We observe that the autocorrelation function (ACF) of an empirical video trace is accurately captured by a shifting-level process with compound correlation (SLCC): an exponential decay for small lags and a hyperbolic one for large lags. Especially, we present a parameter matching algorithm for video traffic. The continuous-time first-order discrete auto-regressive (C-DAR(1)) model, which is a short-range dependent (SRD) video traffic model, can be considered a kind of SLCC process with an exponential correlation term only. Thus, comparing the queuing performances of the C-DAR(1) model and the SLCC with that of a real video trace, it is possible to identify the effects of SRD and LRD in VBR video traffic on queuing performance. From simulation results, we find that LRD may have a significant effect on queuing behavior under heavy traffic loads and large buffer conditions.

Bandwidth renegotiation with traffic smoothing and joint rate control for VBR MPEG video over ATM

Variable bit-rate (VBR) MPEG video traffic is highly bursty due to group of pictures structure, and shows time-variant statistical characteristics due to scene changes. These characteristics make it more difficult to manage network resources, and leads to the significant reduction in network utilization. We deal with the issues related to efficiently transmitting VBR MPEG video traffic over asynchronous transfer mode networks, while maintaining consistent visual quality and improving network utilization on the basis of real-time applications. First, we propose a joint encoder and channel-rate control scheme that comply with not only negotiated traffic parameters, but also constraints imposed by encoder and decoder buffers. Second, we propose a dynamic bandwidth renegotiation method by combining the above scheme with a traffic smoothing method that can make the peak rate close to the sustainable rate. The efficiencies of the proposed methods are compared with a few other competitive schemes such as transmission methods for unconstrained VBR and the constant bit-rate scheme with average bandwidth equal to that of the proposed methods.

VBR video traffic management using a predictor-based architecture

The efficient transportation of real-time Variable Bit Rate (VBR) video traffic in the high-speed networks has been an area of active research. An important issue is the simplicity with which the bandwidth allocation and scheduling schemes can be executed online with real-time constraints in the future high-speed networks. The correlation properties of the VBR video traffic make the predictor-based online traffic adaptation techniques attractive. We developed a novel predictor-based dynamic bandwidth allocation (PDBA) scheme for short-term resource management and studied its queuing performance. In order to reduce the effects of the prediction errors on the queuing system and hence the underutilization of reserved bandwidth, a novel short-term controller (STC) that works at the cell-level has been introduced and the system has been called the PDBA–STC system. This online VBR video traffic prediction-based traffic management scheme has low complexity and is suitable for implementation in high-speed networks Ranganathan et al. [N. Ranganathan, R. Anand, G. Chiruvolu, A VLSI ATM architecture for VBR traffic, Proc. IEEE International Conference on VLSI Design, 1998, pp. 420–427] and has been demonstrated to provide better performance than other existing simple schemes. This paper also investigates the predictability of VBR video traffic that exhibits long-range dependence (LRD) based on a fractional ARIMA (1, d,0) model. The short-range dependent (SRD) Auto Regressive (AR) model for prediction of VBR video traffic has also been considered for evaluation of the proposed dynamic bandwidth allocation scheme and the performance has been compared to that of LRD-based prediction. Finally, a summary and future research have been discussed.

Providing heterogeneous quality of service bounds for correlated video traffic at a multiplexor

Network support for variable bit-rate video needs to consider (i) properties of workload induced (e.g., significant auto-correlations into far lags and heterogeneous marginal distributions), and (ii) application specific bounds on delay-jitter and statistical cell-loss probabilities. The objective of this paper is to present a quality-of-service solution for such traffic at each multiplexing point in a network. Heterogeneity in both offered workload and quality-of-service requirements are addressed. A per-virtual-circuit framing structure and a pseudo earliest-due-date cell dispatcher are introduced to provide guaranteed delay-jitter bounds. Heterogeneous jitter-bounds are supported through software controlled frame-sizes which may be independently set for each virtual-circuit. The framing structure is a generalization of per-link framing introduced by Golestani. The proposed framing structure eliminates correcting for phase mismatches between incoming frames and outgoing frames, necessary in per-link framing. This results in reduction in end-to-end delay bound and buffer requirements, and a simpler implementation. Strong auto-correlations typically seen in video traffic make equivalent bandwidth computations for heterogeneous cell-loss bounds intractable. To address this, the framing strategy is combined with an active cell-discard mechanism with prioritized cell-dropping, the latter utilizing the history of dropped cells and target cell-loss bounds for each virtual circuit. Upper bounds on the equivalent bandwidth needed to support a given workload with a target quality of service are developed. These are validated through numerical and simulation results from variable bit-rate MPEG-I video traces.

Single-pass constant- and variable-bit-rate MPEG-2 video compression

Most real-time MPEG-2 encoders are designed to perform in a constant-bit-rate (CBR) mode, in which buffer constraints are imposed to circumvent large deviations from a desired rate at any instant in time. Although such streams are generally good-quality sequences, certain types of operations or environments call for a more efficient real-time CBR encoder. The first part of the paper describes how a better-quality CBR video stream can be produced by estimating the relative complexity of a picture in comparison with the average complexity of the partially encoded stream and using it to adjust the compression parameters in a single-pass mode of operation. Our CBR encoder is particularly attractive for digital broadcast and editing environments, in which representations of higher-fidelity video objects in both display and freeze modes are constantly pursued. The second part of the paper describes the real-time generation of video streams with a variable-bit-rate (VBR) encoder. This mode of operation is high ly desirable for home entertainment and recreational events. We propose a robust single-pass VBR video encoder algorithm which is capable of learning and adapting itself to the complexity of image segments and thereafter creating streams which have constant visual picture quality. The new VBR scheme displays a better performance than the CBR encoder, particularly when special effects such as scene transitions, fades, or luminance changes are to be compressed. Both CBR and VBR encoders are fully compliant with the MPEG-2 standard and are easily implementable with IBM encoder architecture. Compression results for the new single-pass encoding algorithms and comparisons with previous CBR schemes are provided. The result suggests the suitability of our VBR approach for record/playback in storage media such as digital video disc (DVD) players, disk-based camcorders, and digital videocassette recorders (DVCRs). It further reflects the importance of our single-pass CBR scheme for providers of broadcast services , for which it allows more video programs to be allocated to a selected communication link, and for in-studio applications, for which it greatly facilitates visual analysis of captured streams.

Study of self-similarity in variable bit rate video sources

Variable bit rate (VBR) video will be the predominant application in the future’s multimedia communication networks. Understanding the characteristics of VBR video is important for us to utilize network resources effectively. A brief description of MPEG-1 video sources is given. The essentials of self-similarity and long-range dependence are also presented. Furthermore, some methods of estimating Hurst parameter are described in details. We analyze an hour-long MPEG-1 video trace, and the details of statistical results are discussed. The results highlight that the trace generated by MPEG-1 code has both the short-range dependence and long-range dependence structures.

Flexible optical fiber CDMA networks using strict optical orthogonal codes for multimedia broadcasting and distribution applications

Flexible optical fiber code-division multiple-access (CDMA) networks are proposed to support real-time multimedia communication services of constant bit rate (CBR) and variable bit rate (VBR)/multiple bit rate (MBR). Since strict optical orthogonal codes (OOCs) are employed in incoherent optical fiber CDMA networks, their use can strictly guarantee the correlation constraint /spl lambda/ to be the minimum value (i.e., an unit 1) for multimedia applications. This is achieved without increasing any system complexity compared with the use of conventional OOCs. Moreover, optimal strict OOCs can have the same length as optimal conventional OOCs or a slightly longer length than the latter. It is shown that the proposed optical fiber CDMA networks have a distinguishing feature of high bit-rate flexibility and fast access tunability. Consequently, this can effectively support both VBR and CBR video communications as well as multimedia broadcasting/distributions in a given network without any violation of the minimum correlation constraint /spl lambda/=1. The proposed network can be also used as a backbone to interconnect various local-area networks with different data bit rates. However, conventional OOC-based optical CDMA networks do not possess such characteristics because of violation of /spl lambda/=1 for VBR or MBR communications.

Reliable transmission of high-quality video over ATM networks

The development of broadband networks has led to the possibility of a wide variety of new and improved service offerings. Packetized video is likely to be one of the most significant high-bandwidth users of such networks. The transmission of variable bit-rate (VBR) video offers the potential promise of constant video quality but is generally accompanied by packet loss which significantly diminishes this potential. We study a class of error recovery schemes employing forward error-control (FEC) coding to recover from such losses. In particular, we show that a hybrid error recovery strategy involving the use of active FEC in tandem with simple passive error concealment schemes offers very robust performance even under high packet losses. We discuss two different methods of applying FEC to alleviate the problem of packet loss. The conventional method of applying FEC generally allocates additional bandwidth for channel coding while maintaining a specified average video coding rate. Such an approach suffers performance degradations at high loads since the bandwidth expansion associated with the use of FEC creates additional congestion that negates the potential benefit in using FEC. In contrast, we study a more efficient FEC application technique in our hybrid approach, which allocates bandwidth for channel coding by throttling the source coder rate (i.e., performing higher compression) while maintaining a fixed overall transmission rate. More specifically, we consider the performance of the hybrid approach where the bandwidth to accommodate the FEC overhead is made available by throttling the source coder rate sufficiently so that the overall rate after application of FEC is identical to that of the original unprotected system. We obtain the operational rate-distortion characteristics of such a scheme employing selected FEC codes. In doing so, we demonstrate the robust performance achieved by appropriate use of FEC under moderate-to-high packet losses in comparison to the unprotected system.

Heavy-tailed distribution ofscene duration in VBR video

The authors propose a classification for the scene detection techniques which are commonly used in variable bit rate (VBR) video traffic modelling. Using real video traces we show that scene durations follow heavy-tailed distributions. This heavy-tailed nature is proved to be independent of the technique or the threshold used for the scene detection. This invariant property of video sequences offers a physical explanation for the existence of long range dependence (LRD) in video traffic.

Bandwidth renegotiation scheme for VBR video services

The authors show how the existence of long term variability in variable bit rate (VBR) video traffic imposes the need for bandwidth renegotiation. In particular, two simple scenarios with a fixed renegotiation interval are considered. Using a real MPEG trace, the renegotiation scheme is evaluated to prove its benefits in terms of bandwidth gain and quality of service. The problem of renegotiation demonstrates the need for modelling long term variability in VBR traffic.

A new approach to long-range dependence in variable bit rate video traffic

Recently it has been observed that variable bit rate (VBR) video traffic displays long?range dependence, which suggests that traditional Markovian models may not be suitable for performance evaluation of telecommunications networks carrying this traffic. Inspection of the bit rate profile of VBR video traffic suggests that shifting level processes might be more appropriate for this task. In this paper we show that a particular class of these processes matches the autocorrelation and bit rate distribution of real VBR video traffic, including exhibiting long?range dependent behaviour.

A general AR-based technique for the generation of arbitrary gamma VBR video traffic in ATM networks

Modeling variable-bit-rate (VBR) video source traffic is a crucial issue to evaluate the end-to-end performance of transmitting video signals over asynchronous transfer mode (ATM) networks. Difficulties in source modeling arise from the fact that VBR video source traffic usually follows a gamma distribution with high correlation among adjacent data. Many researchers adopt autoregressive (AR) models driven by a Gaussian error process to account for such correlation. The problem is: due to the closure property of the Gaussian distribution, the traffic so generated is Gaussian rather than gamma. As a remedy, some researchers directly consider gamma AR models instead. Unfortunately, the trouble arises from the fact that the closure property does not apply to gamma distributions, and thus, the linear operation performed by an AR model fails to produce gamma traffic. In this paper, we present a new technique that is capable of generating gamma-distributed traffic with arbitrary correlation while retaining the computational efficiency of Gaussian AR models. The central idea is to decompose given gamma traffic into a linear combination of a number of /spl lambda//sup 2/(1) sequences, and each of these latter processes can be easily obtained from a Gaussian AR process through a simple nonlinear operation. Results based on actual video teleconference data are presented to verify the validity of the new algorithm.

A study of the burstiness of combined MPEG video and audio bitstreams

Variable bit rate (VBR) video is very bursty and its transportation over ATM networks is problematic because bandwidth has to be reserved in advance. Studies have shown that VBR video exhibits statistical self-similarity: it displays structural similarities across a wide range of time scales. To date, studies on the burstiness of MPEG compressed bitstreams have been conducted on the video part only; the audio part has been neglected because of its constant bit rate nature. Furthermore, the change in burstiness of MPEG data which occurs after they have been converted to MPEG-2 transport and ATM bitstreams has not been investigated; a considerable amount of overhead bytes is introduced during the conversion. This paper reports on a study on the burstiness of combined MPEG-1 audio and video bitstreams as found on commercial Video CDs, and the burstiness of these combined bitstreams after they have been converted to MPEG-2 transport and ATM layer bitstreams. We found that there is no increase in burstiness in both situations.

Traffic characterization algorithms for VBR video in multimedia networks

A network that offers deterministic, i.e., worst case, quality-of-service guarantees to variable-bit-rate (VBR) video must provide a resource reservation mechanism that allocates bandwidth, buffer space, and other resources for each video stream. Such a resource reservation scheme must be carefully designed, otherwise network resources are wasted. A key component for the design of a resource reservation scheme is the traffic characterization method that specifies the traffic arrivals on a video stream. The traffic characterization should accurately describe the actual arrivals, so that a large number of streams can be supported; but it must also map directly into efficient traffic-policing mechanisms that monitor arrivals on each stream. In this study, we present a fast and accurate traffic characterization method for stored VBR video in networks with a deterministic service. We use this approximation to obtain a traffic characterization that can be efficiently policed by a small number of leaky buckets. We present a case study where we apply our characterization method to networks that employ a dynamic resource reservation scheme with renegotiation. We use traces from a set of 25–30-min MPEG sequences to evaluate our method against other characterization schemes from the literature.

Modeling full-length VBR video using Markov-renewal-modulated TES models

This paper describes a general methodology for constructing accurate source models of long sequences (full-length movies) of full-motion compressed VBR (variable bit rate) video, directly from empirical data sets of observed bit rate (frame size) records. The main idea is to first cluster scenes into classes and use TES (transform-expand-sample) processes to carefully model their duration and bit rate processes, and then modulate these scene class models by a Markov-renewal process that governs scene transitions. The resulting model is a Markov-renewal-modulated TES (MRMT) process. The fidelity criteria imposed are relatively stringent in that they call for the simultaneous capture of empirical histograms and autocorrelation functions, as well as the qualitative appearance of the empirical data, including burstiness. To illustrate the methodology, the paper provides a detailed description of the modeling procedure, using a JPEG-like coding trace of the Star Wars movie as a working example. The resulting MRMT model was validated by comparing its simulation-based statistics to their empirical counterparts, and by a performance study of the corresponding loss rates for various buffer sizes. The results support the efficacy of the modeling methodology and suggest that suites of realistic and compact source models can be developed for other types of movies under a variety of coding schemes. These may be used to drive realistic Monte Carlo simulations of broadband telecommunications networks.

VBR video: tradeoffs and potentials

The authors examine the transport and storage of video compressed with a variable bit rate (VBR). They focus primarily on networked video, although they also briefly consider other applications of VBR video, including satellite transmission (channel sharing), playback of stored video, and wireless transport. Packet video research requires careful integration between the network and the video systems; however, a major stumbling block has resulted because commonly used terms are often interpreted differently by the video and networking communities. The paper then, has two main goals: (i) to clarify the definitions of terms that are often used with different meaning by networking and video-coding researchers and (ii) to explore the tradeoffs entailed by each of the various modalities of VBR transmission (unconstrained, shaped, constrained, and feedback). In particular, they evaluate the tradeoff among the advantages (better video quality, less delay, and more calls) that were identified by early proponents of VBR video transmission. An underlying theme of this paper is that increased interaction between the video and network design has potential for improving overall decoded video quality without changing the network capacity.

A gamma autoregressive video model on ATM networks

Several works have concluded that the number of cells per frame of variable bit-rate (VBR) video teleconference follows a gamma distribution. But few video models meet this characteristics. We propose a novel video model, called first-order autoregressive (AR) gamma sequence, in which random variables are marginally distributed as gamma variables. We give the definition of a GAR model and a simple realization method of GAR(1). Parameter estimation methods are studied, too. Simulation results show that our model can meet the characteristics of VBR video better than existing models.

Multipath fading effects on integrated video, voice and data transmisson in hybrid-code BPSK-DS/CDMA systems

A possible way to integrate variable bit rate (VBR) services into conventional synchronous direct-sequence, code-division multiple access (DS/CDMA) systems is to assign a number of unique codes (multiple codes) to a given service which can be used whenever its bit-rate exceeds the available channel bandwidth. This has the disadvantage that the number of available spreading codes is reduced. Instead, an asynchronous system can be applied by assigning a common code to all users. However, occasional bit-synchronism in an asynchronous system will cause an unacceptable bit error rate (BER). In our proposed hybrid-code DS/CDMA system common codes are used only for mobile stations (MS) with VBR services if the instantaneous required bandwidth exceeds the available channel bandwidth. A self-control mechanism is applied to guarantee bit-asynchronism between the bits spread by the same code. Simulation-based mobile network traffic models for integrated VBR video, interactive PCM coded speech and bulk transfer of data have been examined to obtain the BER performance of the system. Various channel models have been applied to macrocellular mobile networks.

Scene oriented model for VBR video

A new model for variable bit rate (VBR) video traffic is presented. The model, which could be used as a traffic generator, considers two time scales: scenes, for periods of several minutes, and groups of pictures (GOP), for periods of half a second. To model the scene changes, a Markov chain is used. For the GOP level, a modification for the projected autorregresive (PAR) model is proposed so that the fitting of the autocorrelation function is improved. The model is used to imitate two real MPEG video signals, showing that it is able to accurately capture the behaviour of the real traffic in a queue.

Using adaptive linear prediction to support real-time VBR video under RCBR network service model

A dynamic bandwidth allocation strategy to support variable bit rate (VBR) video traffic is proposed. This strategy predicts the bandwidth requirements for future frames using adaptive linear prediction that minimizes the mean square error. The adaptive technique does not require any prior knowledge of the traffic statistics nor assume stationarity. Analyses using six one-half-hour video tracts indicate that prediction errors for the bandwidth required for the next frames and group of pictures (GOP) are almost white noise or short memory. The performance of the strategy is studied using renegotiated constant bit rate (RCBR) network service model and methods that control the tradeoff between the number of renegotiations and network utilization are proposed. Simulation results using MPEG-I video traces for predicting GOP rates show that the queue size is reduced by a factor of 15-160 and the network utilization is increased between 190%-300% as compared to a fixed service rate. Results also show that even when renegotiations occur on the average in tens of seconds, the queue size is reduced by a factor between 16-30.