Проблемы передачи потокового видео по симплексному каналу сети с потерями данных

Разработана классификация основных проблем и задач, связанных с потерей части информации при передаче потокового видео по симплексному каналу связи, а также направлений в области их решения. Показано, что метод прямого исправления ошибок (ПИО) является наиболее общим подходом защиты от ошибок в рамках рассматриваемой задачи. Проанализированы работы в данной области и показана необходимость разработки нового метода применения ПИО, не привязанного к способу кодирования видеоизображения, с переменно-дискретным коэффициентом избыточности, обладающего низкой сложностью вычислений и обеспечивающего работу в режиме реального времени на современных компьютерах.Розроблено класифікацію основних проблем і задач, пов’язаних з утратою частини інформації при передачі потокового відео симплексним каналом зв’язку, а також напрямків в області їхнього рішення. Показано, що метод прямого виправлення помилок (ПВП) є найбільш загальним підходом захисту від помилок у рамках розглянутого завдання. Проаналізовано роботи в даній області та показано необхідність розробки нового методу застосування ПВП, що не прив’язаний до способу кодування відеозображення, зі змінно-дискретним коефіцієнтом надлишковості, що має низьку складність обчислень і забезпечує передачу даних у режимі реального часу на сучасних комп’ютерах.Classification of problems and tasks related to loss of a part of data in case of video streaming transmission over simplex channel and directions in domain of their solving are developed. It is shown that forward error correction (FEC) is the most general approach to error protection within the scope of the given task. A number of works in the given field are analyzed and necessity of new FEC method development is shown. The method should be independent of video coding scheme, with varying redundancy ratio for each data element and a speed of calculations sufficient for using in real time on modern computers

On combining temporal scaling and quality scaling for streaming MPEG

Temporal Scaling and Quality Scaling are both widely-used techniques to reduce the bitrate of streaming video. How-ever, combinations and comparisons of Temporal and Qual-ity Scaling have not been systematically studied. This re-search extends previous work to provide a model for combin-ing Temporal and Quality Scaling, and uses an optimization algorithm to provide a systematic analysis of their combina-tion over a range of network conditions and video content. Analytic experiments show: 1) Quality Scaling typically per-forms better than Temporal Scaling, with performance dif-ferences correlated with the motion characteristics of the video. In fact, when the network capacity is moderate and the loss rate is low, Quality Scaling performs nearly as well as the optimal combination of Quality and Temporal Scal-ing; 2) when the network capacity is low and the packet loss rate is high, Quality Scaling alone is ineffective, but a combination of Quality and Temporal Scaling can provide reasonable video quality; 3) adjusting the amount of For-ward Error Correction (FEC) provides significantly better performance than video streaming without FEC or video streaming with a fixed amount of FEC. 1

ChitChat: Making Video Chat Robust to Packet Loss

Video chat is increasingly popular among Internet users. Often, however, chatting sessions suffer from packet loss, which causes video outage and poor quality. Existing solutions however are unsatisfying. Retransmissions increase the delay and hence can interact negatively with the strict timing requirements of interactive video. FEC codes introduce extra overhead and hence reduce the bandwidth available for video data even in the absence of packet loss. This paper presents ChitChat, a new approach for reliable video chat that neither delays frames nor introduces bandwidth overhead. The key idea is to ensure that the information in each packet describes the whole frame. As a result, even when some packets are lost, the receiver can still use the received packets to decode a smooth version of the original frame. This reduces frame loss and the resulting video freezes and improves the perceived video quality. We have implemented ChitChat and evaluated it over multiple Internet paths. In comparison to Windows Live Messenger 2009, our method reduces the occurrences of video outage events by more than an order of magnitude

Control of real-time multimedia applications in best-effort networks

The increasing demand for real-time multimedia applications and the lack of quality of service (QoS) support in public best-effort or Internet Protocol (IP) networks has prompted many researchers to propose improvements on the QoS of such networks. This research aims to improve the QoS of real-time multimedia applications in public best-effort networks, without modifying the core network infrastructure or the existing codecs of the original media applications. A source buffering control is studied based on a fluid model developed for a single flow transported over a best-effort network while allowing for flow reversal. It is shown that this control is effective for QoS improvement only when there is sufficient flow reversal or packet reordering in the network. An alternate control strategy based on predictive multi-path switching is studied where only two paths are considered as alternate options. Initially, an emulation study is performed, exploring the impact of path loss rate and traffic delay signal frequency content on the proposed control. The study reveals that this control strategy provides the best QoS improvement when the average comprehensive loss rates of the two paths involved are between 5% and 15%, and when the delay signal frequency content is around 0.5 Hz. Linear and nonlinear predictors are developed using actual network data for use in predictive multi-path switching control. The control results show that predictive path switching is better than no path switching, yet no one predictor developed is best for all cases studied. A voting based control strategy is proposed to overcome this problem. The results show that the voting based control strategy results in better performance for all cases studied. An actual voice quality test is performed, proving that predictive path switching is better than no path switching. Despite the improvements obtained, predictive path switching control has some scalability problems and other shortcomings that require further investigation. If there are more paths available to choose from, the increasing overhead in probing traffic might become unacceptable. Further, if most of the VoIP flows on the Internet use this control strategy, then the conclusions of this research might be different, requiring modifications to the proposed approach. Further studies on these problems are needed