A Research On A Time Synchronization Technology Of Distributed Video Applications

With the rapid development of multimedia technology and information communication technology,the display and distribution technology of multimedia content are also improved every day.The distributed video display system based on video over IP(VOIP)technology has some advantages such as flexible architecture and low cost etc.,and is widely used in aerospace,security and many other fields.However,because the human eye is very sensitive,it is easy for people to notice the video sync problem where the video sync difference is larger than 42 milliseconds.This puts a high requirement on the synchronization performance of distributed nodes in the VOIP video display system.Therefore,the performance of synchronization is the key parameter of the VOIP distributed video display system,which directly affects the further development and application of the system.Based on the research of state-of-the-art video synchronization technology and the advantages and disadvantages of time synchronization technology in other fields,a time synchronization technology suitable for VOIP distributed video display system is proposed in this thesis.The detail work content is listed as follows:1)Based on the research on the synchronization performance of the existing VOIP distributed video display system,calculating and analyzing the range of jitter and deviation among the terminals under normal working conditions.Since the timing accuracy of the current Internet timing system cannot meet the requirement of VOIP distributed video display system,a private timing node based on the master-slave clock synchronization structure is developed in this thesis,and a standard time for the distributed display system is provided by designating a unique device as the primary clock;2)To overcome the non-ideal factors such as network distribution delay deviation,distributed node inter-crystal frequency deviation and long-term jitter in distributed systems,a two-way time difference delay algorithm is developed based on the time communication model.This can compensate the actual network path delay and improve the accuracy of the network timing further;3)Since the video stream possesses the characteristic of high frame rate(?30fps)and continuous,not only the system needs to be synchronized quickly,but also the video playback is required to be fluent during the synchronization process.To meet the above requirements at the same time,the correction algorithm of mixed soft and hard adjustment is proposed in this thesis.Judged by threshold value,one of direct correction and frequency compensation correction method is chose.This correction algorithm can make the system synchronize with the standard time quickly and stably for different time deviations in different situations;4)Estimate the possible network faults of the time synchronization system and provide a solution.Real-time monitoring and control of the system's synchronous communication status ensure that the system work reliably for a long time.Finally,to verify the design of this thesis,the time synchronization function is tested on the FPGA hardware platform.It is verified that the system can quickly realize the time synchronization function of each node in a short time(10 frames / sec,0.2-0.3 seconds),and the synchronization precision reaches ±1 microsecond,which meets the basic needs of video applications and has some social and economic value.