Quality-optimised MPEG2 video data rate control using fuzzy logic techniques

Scalable High Efficiency Video Coding (SHVC) is the scalable extension of the latest video coding standard H.265/HEVC. Video rate control algorithm is out of the scope of video coding standards. Appropriate rate control algorithms are designed for various applications to overcome practical constraints such as bandwidth and buffering constraints. In most of the scalable video applications, such as video on demand (VoD) and broadcasting applications, encoded bitstreams with variable bit rates are preferred to bitstreams with constant bit rates. In variable bit rate (VBR) applications, the tolerable delay is relatively high. Therefore, we utilize a larger buffer to allow more variations in bitrate to provide smooth and high visual quality of output video. In this paper, we propose a fuzzy video rate controller appropriate for VBR applications of SHVC. A fuzzy controller is used for each layer of scalable video to minimize the fluctuation of QP at the frame level while the buffering constraint is obeyed for any number of layers received by a decoder. The proposed rate controller utilizes the well-known structural similarity index (SSIM) as a quality metric to increase the visual quality of the output video. The proposed rate control algorithm is implemented in HEVC reference software and comprehensive experiments are executed to tune the fuzzy controllers and also to evaluate the performance of the algorithm. Experimental results show a high performance for the proposed algorithm in terms of rate control, visual quality, and rate-distortion performance.

Evaluation of ABR traffic management under various system time scales

Since they are delay tolerable, the ABR applications can be allocated the remaining resources after CBR (constant bit rate) and VBR (variable bit rate) applications have been accommodated. To avoid excessive losses, the transmission rates of the ABR applications should be modulated by the amount of remaining resources. That is, the ABR rates should be controlled through a feedback based rate control mechanism. A network link shared by remote ABR and VBR applications is considered and the impact of various system time scales on the effectiveness of the feedback based flow control scheme is investigated. These time scales are expressed in terms of the network transmission speed, the minimum tolerable ABR rate and the rate of change of the VBR source rate. While the negative impact of a decreased network time scale on the effectiveness of this control scheme is well known, the impact of the ABR and VBR time scales has not been investigated in the past. It turns out that for a given network time scale, the induced cell losses can be significantly reduced for increased ABR and/or VBR time scales and thus, the latter time scales should be taken into consideration when evaluating the effectiveness of an adaptive feedback based rate control mechanism.

A fuzzy bit allocation method, applicable to many rate control algorithms targeted for variable rate video applications, is proposed in this paper. In low-delay video communication applications, a constant short-term average bit rate is required. However, in variable bit rate applications, such as streaming and broadcast applications, a constant long-term average bit rate is sufficient and a higher short-term variation in bit rate is acceptable. A variable bit rate video can provide better visual quality and coding efficiency in comparison with a constant bit rate video. The proposed fuzzy bit allocation algorithm is employed for encoding special P frames. To take advantage of variable bit rate video, the proposed method is implemented independently of the rate control algorithm. Two fuzzy systems are used to determine the location and the quantization parameter of special P frames. The proposed method is implemented on a JM H.264/AVC video encoder. Experimental results show that it can improve the quality of compressed video while having a low degree of computational complexity.

A joint rate control algorithm for variable bit rate(VBR) MPEG-compressed digital video on point-to-point permanent virtual circuit (PVC) ATM links is proposed.The algorithm controls the encoding mode of a numberof video encoders that operate either on VBR or constantbit rate (CBR) mode. The algorithm selects the encodingmode based on the buffer occupancy of a multiplexer co-located with the encoders that interfaces them to the PVClink. VBR encoding is the predominant encoding mode usedduring congestion-free periods. CBR mode is used only during congested periods. When CBR is selected, new bit ratesare jointly assigned to the encoders based on their relativeencoding complexities. The bit rate assigned to the encodersare enforced by a CBR rate control local to each encoder.The performance of the joint rate control algorithm is evaluated through simulation of a packet multiplexer, where anumber of connections are multiplexed onto a fixed-capacity channel. The performance is compared to that of multiplexing conventional CBR and open-loop VBR from the videoquality and bandwidth efficiency points of view. Simulation results show that the proposed algorithm improves performance over multiplexed conventional CBR or open-loop VBR MPEG video, without significantly increasing implementation complexity. The application of the algorithm, tovideo-on-demand over ATM is discussed.

To satisfy the rigorous limitation of delay in real time transmission of high quality video, the coding rate and transmission rate should be selected judiciously. For the ATM variable bit rate (VBR) channel, the channel rate is tightly restrained by the traffic contract negotiated before communication. The leaky-bucket based rate control algorithm proposed by us could meet the delay and traffic contract, so as to abstain the cell loss over the user-network interface (UNI). Furthermore, in order to benefit the statistical multiplexing and improve the overall decoded video quality, the burstiness of the MPEG encoded stream is reduced dramatically in our system. Our experiment shows that the algorithm is a good compromise between CBR (constant bit rate) and VBR video coding. And its implementation is so simple that it could be easily utilized in on-line rate control for real-time video communication.

The digital standard definition television (SDTV) encoder is a very important part of the digital TV broadcast chain. Most real-time MPEG-2 encoders are designed to perform in a constant bit-rate (CBR) mode. But an even better compressed stream can be created by employing a variable bit-rate (VBR) encoding algorithm. VBR can be exploited as a means of achieving statistical multiplexing for digital broadcast satellites. This paper suggests an implementation procedure of an SDTV video encoder and proposes a novel VBR bit-allocation strategy that could be implemented in this encoder system. First, using a rate-quantization model and rate-quantization perceptual model, a real-time VBR bit-allocation strategy is deduced. In this strategy, more (or fewer) bits are allocated to "difficult-to-encode" (or "easy-to-encode") groups of pictures (GOPs), which are distinguished according to the estimated encoding complexity of the GOPs. After allocating an appropriate number of bits to each GOP by using this VBR bit-allocation strategy, we use a CBR rate control algorithm to allocate a number of bits and select a quantization scaler for each picture of a GOP. Then smooth visual quality is achieved not only in a GOP but also in the whole video sequence. Second, the system implementation of an SDTV video encoder including a video input module, a video encoding module, a system control and rate control module (SCRCM), and a PES packetizing module is described. We also discuss in detail how to implement our real-time VBR bit-allocation strategy in the SCRCM. Finally, experimental results demonstrate that our proposed VBR encoder displays a better performance than the CBR encoder.

Compressed digital video can be transported on ATM networks using either a constant bit rate (CBR) or a variable bit rate (VBR) network transport service. The use of VBR transport is generally considered to offer some potentially attractive advantages over more traditional CBR transport. These potential advantages include the expectation of improved reconstructed video quality, shorter end—to—end delays and improved statistical multiplexing performance. Unfortunately, most evaluations of the relative end—to—end performance of VBR versus CBR transport of digital video fail to adequately take into account the effects of lost cells in transporting multiple VBR streams which compete for limited network resources. These effects can be avoided with CBR transport using appropriate call admission control (CAC) procedures. Furthermore, these relative performance evaluations are generally not provided under comparable levels of network resource utilizations. Indeed, no methodology presendy exists for fairly assessing the relative end—to—end performance of CBR and VBR encoded video at the same level of resource utilization. In this paper, we develop and illustrate a methodology for comparing the relative performance, in terms of the corresponding end—to—end distortion, of CBR and VBR encoded digital video transport for fixed network resources and at identical multiplexing levels. The approach is an extension of a previously developed joint source—channel coding approach for VBR digital video transport on ATM networks. Our objective in this paper is to provide a common comparison framework for CBR and VBR video streams.

We propose a scheme for efficient transport of video over wireless networks using a novel rate control scheme. The explicit bit rate (EBR) control specifies the use of a variable rate channel and provides an adaptively varying requisite bandwidth to carry varying video encoded output. Due to the use of prediction and variable length codes (VLC) for video codecs, variable-bit-rate (VBR) encoding is considered logical in all advanced video encoders, such as H.263 and H.264. The VBR method of rate control which is currently employed in 3G networks requires the use of a constant bit rate (CBR) physical channel to carry video transmissions to ensure a fixed bandwidth channel to the user during a video call. However, a constant bit rate channel can result in delivering video frames in unequal time intervals, delays in transmission and poor video quality at the end user. We show the application of an explicit bit rate (EBR) control mechanism for high efficiency and quality video transmission for both cdma2000 1x and WCDMA wireless networks.

MPEG-2, the international standard of the ISO/IEC, is a key technology for video coding and is widely used in digital television etc. Its most frequently used coding rate control is the constant bit rate (CBR) mode. CBR's bandwidth requirement is relatively low, but it needs further improvement in terms of the coding efficiency. On the other hand, the variable bit rate (VBR) mode may be able to enhance the picture quality in situations that are rich in bandwidth or in storage media such as DVD. We have already developed a one-chip MPEG-2 video encoder LSI (SuperENC) to cope with the broader range of digital image communication applications. This paper discusses a new one-pass VBR coding control algorithm based on mathematical relations among coding parameters such as quantization parameter, bit rate and decoded image distortion. Our aim is to solve the problems of conventional techniques and verify the algorithm's effectiveness through hardware implementation. A one-pass VBR control function was implemented in the chip's firmware. Not being a very complex algorithm, it is robust with respect to abrupt scene changes. The SNR gain in a TM-5-based CBR mode was 1.5 to 1.8 dB, and the bit rate reduction under the same subjective quality was 10-30 %.

A mixed bit rate (MBR) video coding method is presented for asynchronous transfer mode (ATM) networks which has communication compatibility between constant bit rate (CBR) video codecs and variable bit rate (VBR) codecs. In MBR video coding, essential information is encoded at a CBR by using a conventional CBR coding method such as H.261 and enhancement information is encoded at a VBR to attain constant image quality. To realize the MBR coding of video, the conventional embedded pulse code modulation (PCM) quantization is extended by applying the requantization method only to the least significant bit (LSB) of the quantizer output. In the EX-EMB PCM method, the most significant part and least significant part (MSP/LSP) separation of embedded PCM and an additional threshold for the requantizer are dynamically determined to attain a desired distortion. The MBR codec with EX-EMB PCM was evaluated by computer simulations. The simulation results showed that the proposed method was effective not only for improving video quality but also it prevented the degradations of image quality at the scene change by increasing the bit rate for the VBR channel. >

In this paper, two combined power and rate control (CPRC) algorithms, without-priority CPRC and priority-based CPRC, are proposed for the uplink of a cellular system integrated constant bit rate (CBR) voice and variable bit rate (VBR) data transmission. The CBR users and the VBR users are treated equally when assigning power and rate by the without-priority CPRC algorithm; while the CBR users are given higher priority by the priority-based CPRC algorithm. Simulation results demonstrate that the proposed algorithms can provide better performance than SPC (selective power control) algorithm proposed by S.-L.Kim. Comparing with the without-priority CPRC, the priority-based CPRC can provide lower outage probability for CBR users and less transmission power at the cost of throughput of VBR users under heavy system load.

This paper considers the problem of power management and throughput maximization for energy neutral operation when using an energy harvesting sensor (EHS) to send data over a wireless link. The EHS is assumed to be able to harvest energy at a constant rate, and use a fixed part of the energy harvested in a slot for measuring the channel state. The rest of the energy harvested is available for transmission, however, it can be stored in an inefficient battery if it is not fully utilized. The key constraint that the EHS needs to satisfy is energy neutrality, i.e., the expected energy drawn from the battery should equal the expected energy deposited into the battery. In this scenario, two popular models for data transmission are contrasted: the constant bit rate (CBR) model and the variable bit rate (VBR) model. In the CBR model, it is assumed that the EHS are designed to transmit data at a constant rate (using a fixed modulation and coding scheme) but are power-controlled. In the VBR model, the EHS selects both the transmit power and the data rate of transmission in each slot based on the channel instantiation. A framework under which the system designer can optimize several parameters of the EHS that determine the average data rate performance when the channel is Rayleigh fading is developed. Using this framework, the two transmission schemes are contrasted. It is shown that, with the right choice of parameter settings, the CBR scheme can perform nearly as well as the VBR scheme at significantly lower complextiy. The usefulness and validity of the framework developed is illustrated through simulations for specific examples.

A high quality variable bit rate (VBR) MPEG- 2 encoding scheme that offers optimum video quality and bandwidth allocation is presented. The proposed scheme is very easy to implement and offers a very efficient real time VBR solution for broadcasting applications that involve multiplexed distribution of multiple video sources. A High Quality Pseudo VBR MPEG Encoding Process The advantage of variable bit rate (VBR) video over constant bit rate (CBR) is that it preserves picture quality regardless of the video content and offers optimum bandwidth allocation so that a potentially greater number of multiplexed VBR streams may be transmitted over a given bandwidth. Several different implementations of statistical multiplexing of multiple video sources and optimization of bandwidth allocation using VBR streams have been reported in the literature. However, the generation of VBR streams has not received the attention it deserves. In many cases, VBR streams are either obtained by using fixed quantization levels and multiplexing controllers or by assuming multi-layer implementations of the MPEG compression standard. These "non-true" VBR streams do not depend entirely on picture quality and thus do not closely represent the VBR distribution that is found in actual broadcasting applications. In video production and real-time broadcasting applications, rapid scene changes and excessive motion increase the differences between consecutive frames and as a result have a very negative impact in the perceived quality of the video. To overcome this problem, adjustment of the "standard frame sequence is necessary in order to accommodate for the extra information needed to accurately represent drastic changes between adjacent frames. We developed a method which automatically adjusts the frame sequence and the number of bits needed to represent each frame depending on the video content. The result is a significant improvement in video quality. Our method uses a large 30 frame GOP which allows for efficient redistribution of bits while introducing maximum delay of three frames. Redistribution of bits is based on a "smart" combination of SNR, quantization and motion activity information for each frame. Large 30 frame GOP's tend to have a significant number of low motion frames which are "starved" by ow algorithm thus saving bits for more active frame sequences. In addition, I frames are forced by our method on scene cuts thus introducing more than one I frame within a GOP and preventing long propagation of impairments due to rapid changes. Although the bit rate can be kept constant for every GOP, the increase of the GOP size in combination with our smart redistribution of bits generates a pseudo VBR stream effect which results in considerable improvements in video quality. Performance evaluations have shown that for the same picture quality our method improves the compression rate by at least 25%. The video streams generated by our encoder were successfully played back by all the existing hardware and software MPEG-1 and MPEG-2 players. A Real Tie VBR MPEG.2 System

An efficient cell scheduling algorithm is proposed for multiplexing traffic sources with variable bit rate requirement in an ATM multiplexer. Three types of traffic sources an assumed in the multiplexer, namely the constant bit rate (CBR), variable bit rate (VBR), and best-effort traffic. For VBR and CBR sources, a statistical bandwidth requirement should be claimed before they are multiplexed in the ATM outgoing link. The proposed algorithm dynamically schedules the traffic and preserves the claimed throughput in the outgoing link for each CBR or VBR source. When there is no cell arrival at the VBR or CBR sources, the proposed algorithm assigns the bandwidth to the best-effort sources. The performance of the proposed algorithm is evaluated via simulation. The result shows that the proposed method has better performance over other static multiplexing schemes such as the weighted round-robin method.